HFTA - ARRL
Contents
1. From the USGS DEM Digital Elevation Model maps database From the USGS NED seamless electronic maps National Elevation Database From SRTM 3 arc second electronic maps Shuttle Radar Topography Mission for areas outside the USA sari cae ae Some sample data files are included with HFTA for example N6OBV 45 00 PRO and N6BV 330 00 PRO meaning N6BV to Europe at 45 azimuth and to Japan at 330 My old station was located on a small hilltop in Windham New Hampshire These sample files have PRO filename extensions meaning PROFILE They were created from DEM electronic maps Latitude Longitude at Your Tower Base One important piece of information you will need is the position of your tower One way to get this is to place a hand held GPS receiver out at the base of your tower Note that you may have to smooth out the latitude longitude GPS data by taking a number of measurements and then averaging them to obtain an accurate location for your tower Another way to determine your tower position is to use Google Earth to find your street address zoom in and then home in on the exact latitude and longitude of your tower You should record the position of the base of your tower in your notebook for later use The Old Fashioned Paper Map Way The old fashioned way to prepare a terrain profile was to buy an actual paper USGS topographic map and painstakingly measure out the terrain data starting at a point representing2. W1 MA AS PRN a W1 MA EU PRN Elevation statistic files PRN Open as read only W1 MA JA PRN W1 MA OC PRN W1 MA SA PRN W2 NY AF PRN W2 NY AS PRN W2 NY EU PRN W2 NY JA PRN W2 NY OC PRN W2 NY SA PRN W3 DC AF PRN W3 DC AS PRN W3 DC EU PRN W3 DC JA PRN W3 DC OC PRN W3 DC SA PRN W4 AL AF PRN v Fig 3 Selecting Elevation Statistical Files CHANGING THE FREQUENCY 3 3 a a a a a ia 2 a a a a a a a 4 see You can edit the frequency by clicking in the Frequency box on the main HFTA window The elevation angle statistical data is automatically updated when you enter a different frequency Page 4 HFTA RESULTS Fig 4 shows plots for four terrains after clicking Compute BVCAPE 45 PRO is for my old QTH on Cape Cod KSMA 45 PRO is the profile of my next door neighbor KSMA on Cape Cod Both terrain profiles are for the 45 azimuth towards Europe Terrain Files 3 and 4 FLAT PRO are over flat ground with antennas at 70 and 100 feet respectively These serve as references to show what happens in the absence of irregular terrain The antenna heights shown in Fig 4 were those of our actual 20 meter Yagis N6BV s was at 70 feet while KSMA s was at 80 feet Output Graph HFTA x TES Freq 14 2 MHz HFTA Copyright ARRL 2003 2004 by N6BV Ver 1 03 Max Gain 15 3 dBi BVCAPE45 PRO 70f
3. Write down the quad names surrounding your location If your location is near the edge of a quad map as many locations are you will need to download not only the quad map for your location but also other nearby quads You may find it necessary to download and merge as many as four different quads to cover a given location if it is located in the corner of its main quad map For my old location in Windham Page 18 NH I found it necessary to download the Derry quad in addition to the Windham quad and merge the two a Digital Raster Graphic Aerial Satellite Topos DEMs Street Maps Vector Demographics a HOME Software Services Samples FAQ Contact Help Pricing SelectArea Click on your area of interest 1 24K 7 5 or 7 x 9 Mile Are Q C Zoom In amp Zoom Out Re Center Zoom to a State il C 24k Quad Info i Census Info View U S Base Map x Satellite DEM KY 250K Topo ey Cue Z e pee I Display Coordinates Map Width 40 miles Fig A3 Result of zooming out four levels after searching for the exact street address at N6BV s old QTH in Windham NH The red star shows the N6BV location bounded by topo maps labeled Windham Derry Salem Depot and Sandown Note checkbox Display Coordinates at lower left that allows you to display latitude longitude at the cursor if you wish Download DEMs Go to this UR
4. 10 After unzipping Page 26 The first file in Fig 10 the one with the flt float extension is the file you would open using MicroDEM to bring up a map The rest of the files in the example subdirectory are also needed by MicroDEM However once you bring up a MicroDEM map you can save it as a MD DEM file and erase the float directory and files Page 27 Getting Digital Map Data Outside the USA DOWNLOAD AN SRTM FILE The US government has released digital terrain data that covers 80 of the world between 60 N and 54 S latitudes The survey data was generated during a NASA Space Shuttle mission in February 2000 and is called SRTM Shuttle Radar Topography Mission data Inside the continental USA parts of Alaska Hawaii Puerto Rico and certain US Territories in the Pacific SRTM data is available with a resolution of 1 arc seconds roughly 30 meters Outside these areas the US government has restricted the resolution to 3 arc seconds roughly 90 meters Still the SRTM digital data is easier to use to generate terrain profiles for HFTA than are any manual mapping methods The easiest way to download 3 arc second SRTM Shuttle Radar Topography Mission data that covers most of the world is to go to the website for the CGIAR Consortium for Spatial Information http srtm csi cgiar org SELECTION inputCoord asp You will see a worldwide map with clickable blocks covering ar
5. 13 000 feet 4000 meters because even at that distance the effect is noticeable on elevation pattern for low frequency antennas like a 40 meter Yagi HFTA will accept input of up to 149 data points in an input terrain file as mentioned before This method of producing terrain data manually is extremely labor intensive It was also hard on the eyes requiring a good magnifying glass and a steady hand with a set of calipers to measure off the distance on the horizontal scale at the bottom of the paper map For relatively uncomplicated terrains that is ones not located in rugged mountains I could complete a single azimuth s data profile in about a half hour To show all azimuths of interest boxing the compass as mariners are found of saying takes a very long time TECHNOLOGY TO THE RESCUE MICRODEM Kevan Nason NS4T brought to my attention a really fine program that manipulates electronic topographic data The mapping program is called MicroDEM and a professor at the US Naval Academy Dr Peter Guth is the author Professor Guth and the US Naval Academy have graciously allowed ARRL to put MicroDEM on the CD ROM that accompanies this book MicroDEM automatically makes numerous terrain profiles once you have downloaded the appropriate electronic map files described in detail later in this Appendix VERSIONS OF MICRODEM The version Alpha 7 of MicroDEM that is included presently on the CD ROM that accompanies this edition of Th
6. What we want now is for MicroDEM to generate terrain profiles in 5 steps of azimuth with a radius of 4400 meters around your tower base This represents enough distance for HFTA to create accurate reflection and diffraction ray tracings to compute the far field elevation responses Presuming that you have a map on screen that covers the desired area now click on Calculate Intervisibility Viewshed menu You can also click on the Weapons Fan icon on the top of the map window for this if this icon is showing at the top of the map Double click anywhere on the map and a data entry box will open where you enter the exact latitude and longitude at your tower Once you have entered these numbers and have clicked OK another form Viewshed Parameters will open See Fig A13 x Fan name TESTI feast act_ C ASL AGL Observer range m 4400 Observer AGL m Target C ASL AGL 2 Target AGL m Max inclination 89 jo Left boundary Min inclination 89 Right boundary 355 Color amp algorithm Min range m jo V Report coverage Range Units MV Outline fans V Graph coverage C ft C yds m Siro V Save radials Opacity X Cancel Help Pah Fig A13 Setting the ViewShed Parameters Note the Save Radials checkbox toward the bottom of the form Make sure it is checked The Fan name at top is the filename base under which the azimuthal profiles will be saved In the
7. finding the specific DEM s for a particular tower location can involve quite a bit of hunting around at several Web sites and you also must know the counties in which various quads are located In general I recommend DEM files despite the merging challenges since the absolute accuracy of the DEM files appears to be better than of the smoothed seamless NED files especially on challenging terrain such as on a mountaintop You need to know several simple facts before attempting to download DEM digital terrain data from the Web the state and county and possibly the ZIP Code too It is very useful to have an exact street address as well which you can often find at http www qrz com You will find that it may not be immediately obvious what names the USGS US Geologic Survey has used to label their quad 1 24000 topographic maps To see an overview map that shows the quad names near your location go to the following URL for MapMart http tinyurl com g8hleu You will be presented with a map of the entire USA The easiest way to find an exact location is by specifying the street address by clicking in the Zoom to drop down box in the upper left hand corner See Fig A3 The red star was the location of the N6BV mailbox at the front of the property when I lived in New Hampshire You will need to Zoom Out to see the names of the quad topo maps surrounding your target location Place the cursor on the red arrow when zooming out
8. sized circles surrounding your tower location I recommend radii of 2200 and 4400 meters First check the box Draw range circles Now click on the O Range circles button and then type 2200 for the first range ring and 4400 for the second Click OK to exit this window e Set the default subdirectories by clicking the Directories tab MicroDEM creates a subdirectory system where map data will be stored usually in x Mapdata where the x denotes the disk drive you select during installation The radial PRO files you will be creating later will be stored in the x Mapdata MD PROJ Fans subdirectory e Generate a Weapons Fan to set additional default parameters First load the HangRockCanyon sample DEM map using the File Open Open DEM menu selections Then click Calculate Intervisibility Viewshed Move the cursor near to your location and double click the mouse Type in the desired latitude and longitude and then click OK A new ViewShed Parameters window will open as shown in Fig A2 Make sure you check Save radials so that terrain profiles will be saved to disk x Fan name TESTI Observer C ASL amp AGI Observer range m 4400 Observer AGL m 2 Cas G AGL 2 Target AGL m Aas Max inclination a9 Left boundary jo Min inclination j 89 Right boundary 355 Color amp algorithm Min range m jo a V Report coverage Range Units V Outline fans M Graph coverage Ct C yds m _ Outline V Save ra
9. text box at the top in Fig A13 you choose a name for MicroDEM to use for subsequent map operations perhaps N6BV 1 for the first tower location at a particular site The filename you specify will be what HFTA will use For example if you specify N6BV 1 MicroDEM will create 71 files at 5 degree intervals labeled N6BV 1 0 00 PRO N6BV 1 5 00 PRO N6BV 1 10 00 PRO up to N6BV 1 355 00 PRO Writing to disk takes about 5 seconds on a 1 GHz Pentium 3 computer running Windows 2000 Professional Note that MicroDEM places the PRO files in the subdirectory x Mapdata MD PROJ FANS where x is the subdirectory you chose on the Options Directories tab You may Page 30 want to move these files manually using Windows Explorer to another subdirectory of your choice after you finish working with MicroDEM Click the Observer range m text box and verify that it is 4400 meters the default Set the Right Boundary to 355 degrees Make sure you have clicked the selection Save radials at the bottom Don t worry about setting the Observer AGL m or Target AGL m values They re set at default values of 18 m 60 foot tower and 2 m the height of a soldier Click OK to finish creating the profiles Page 31 Other MicroDEM Capabilities BRING ON THE TIGER This next step is not totally necessary but it significantly adds to the process if you can visualize how your terrain relates to the roads and streets near your l
10. tif file and the associated zip file because you won t need them anymore ANOTHER NED SOURCE The USGS United States Geologic Survey maintains a web site they call the The National Map Terrain data at this site is available in several formats including some limited GeoTIFF data described in the last section However the web site changes quite a lot as they built it out and trying to figure out where they ve stashed things can be frustrating The URL is http viewer nationalmap gov viewer Click on the light blue arrow icon labeled Download Data at the upper right of the screen A drop down menu will appear and you will click on the link at the bottom labeled Click here to download by coordinate input This will open a box like Fig A7 but will only accommodate input in decimal degrees of latitude and Page 24 longitude As in the previous method for gathering NED data specify the upper and lower limits for latitude and longitude plus and minus 0 1 of the station s position Bounding Box from coordinates Decimal Degrees Enter the limits for a new area Fie and Western Southern lear Fields Fig A7 Input bounding box Use decimal degrees to enter bounding latitudes and longitudes that is plus or minus 0 1 degrees of the station s position When you ve finished defining the bounding box be careful to specify West longitudes in the US as negative numbers click the Dra
11. top menu followed by Save DEM and then DTED Make sure that the Lat spacing seconds and Long spacing seconds are set to 3 for 0 3 seconds Click on OK and save this as Dem2 DT1 Close the dialog boxes and the map e Now merge the two DTED files Click on File in the top menu and then click Data Manipulation followed by Merge and DEMs and DEMs pick single Again it may be useful to type DT1 followed by Enter in the Filename box to bring up only the DT1 files you have created e Select Dem1 DT1 followed by Dem2 DT1 Click on Cancel to exit the merge function and name the file something else again perhaps N6BV 1 DEM Close the dialog boxes and the map Again luckily you won t have to do this special merging procedure too often SEAMLESS NED MAPS MicroDEM can also use a seamless NED file to create a custom sized topographic map centered on the latitude longitude you specify for the tower s base The latest URL for the MRLC seamless data site is http www mrlc gov viewerjs The default setting for downloading data is Page 21 1 NED which is what we need in the USA Fig A5 shows the page that comes up for USGS Seamless Data Distribution Note Be aware that USGS seems to change this page often Fig A5 Initial setup window for MRLC Seamless Data page The Data dropdown menu shows the Download Tool icon The next screen will be
12. Bi 3 Ele 7 0 dBi 4 Ele 8 5 dBi 5 Ele 9 5 dBi 6 Ele 11 0 dBi 8 Ele 12 0 dBi Use for out of phase drive e g 90 Cancel OK Fig 2 Entering antenna types and heights for each terrain file SELECTING THE TYPE OF YAGI USED Clicking on the button at the right down arrow in an Antenna box will open a drop down menu of antenna types available including a dipole and Yagis with as few as 2 elements all the way to 8 elements The gains in free space for these antennas are shown below in Table 1 along with the boom lengths needed on 20 meters to achieve these gains Table 1 Free Space Gain dBi and Boomlengths on 20 Meters Antenna Dipole 2 Ele 3 Ele 4 Ele 5 Ele 6 Ele 8 Ele Gain 2 15 5 5 7 0 8 5 9 5 11 0 12 0 20 m Boom 8 16 26 40 60 80 OUT OF PHASE FEED There is a useful feature in HFTA that earlier versions such as YT didn t have You may choose to use out of phase drive to individual antennas in a stack You do this by appending an asterisk to the end of a height number For example in a stack at 90 60 and 30 feet you might run the top 90 foot high antenna out of phase with the two lower Yagis Enter 90 in the top left text box Although employing out of phase drive is not often useful in terms of increasing the overall performance of a stack of Yagis sometimes it can cover high angles that a stack or any single antenna cannot accomplish because
13. L to download the DEMs http data geocomm com dem demdownload html You must register once for free downloading of DEMs on this site On the USA map shown in Fig A4 click on your state and select your county Click on the link Digital Elevation Models DEM 24K The label 24K refers to the fact that this topo map has a scale of 24 000 1 Now select the name of the quad you want to download and click the green Download button for that quad USGS DEMs Please Click on a State to access DEM data Puerto Rico DEMs Click Here Fig A4 USGS map selector screen Click on your state Page 19 You will be presented with a link to click on with a label similar to this 1667372 DEM SDTS TAR GZ 30 meter When saving the map to disk I usually edit this confusing numerical name to something I can relate to such as Windham_NH SDTS TAR GZ to describe my old location in New Hampshire Note that you might have a choice of data in increments of either 10 or 30 meters Choose the 30 meter data since the degree of precision in the 10 meter data is not warranted for HF work and because 10 meter DEM files take far longer to download If there is no choice other than 10 meter data as may happen for newer data sets MicroDEM can still automatically create 30 meter terrain profile information for HFTA to use Merging Topographic Maps As mentioned above at my old location in Windham NH I needed to merge two DEM maps because my
14. NTAINS Some terrains may have tall mountain peaks that are further than 4400 meters from your tower base I normally recommend that you specify a distance of 4400 meters and a spacing of 30 meters between distance samples in MicroDEM HFTA can handle up to 149 data points 150 including the tower base so a typical PRO file will contain 149 points You can manually edit a terrain file to include a 5 000 meter peak at say 8000 meters away by deleting the last line in a file and then adding a line using an ASCII word processor saying 8000 5000 ACCURACY AND TESTING THE RESULTS What would I estimate as the accuracy of HFTA elevation predictions I would say that I would trust the results within plus minus 3 dB In other words take HFTA results with a grain of salt Don t obsess with changing the height of your antenna by fractions of a foot to see what happens Having said that now I must state that it is a good idea to compare elevation patterns in intervals of perhaps 1 foot to assess whether HFTA is generating reasonably smooth results Often the 14 steps used in the program don t align exactly and artificial spikes or holes can be created This is inherent in any ray tracing program and can only be eliminated by using extremely small angular step increments and doing so would slow down execution even more After I do an evaluation for a particular antenna height I will often specify an overlay of three heights se
15. Operating Instructions for HFTA Version 1 04 HF Terrain Assessment for Windows February 22 2013 This version of the HFTA Operating Instructions updates the method to download terrain data files from the NED National Elevation Database USGS online servers The MicroDEM program then can be used to create terrain profiles for HFTA using USGS map data in DEM Digital Elevation Model or NED National Elevation Database seamless formats in the USA In addition usage of SRTM Shuttle Radar Topography Mission 3 arc second format is described allowing the user to generate terrain profiles for areas outside the USA See Appendix A for instructions on downloading and using digital terrain data PREFACE HFTA is a ray tracing program designed to evaluate the effect of foreground terrain on the elevation pattern of up to four multi element HF monoband Yagis in a stack See Chapter 3 in the 21st Edition of The ARRL Antenna Book for details about the theory behind ray tracing and diffraction in HFTA HFTA has a vastly improved operator interface compared to older DOS versions of its predecessor programs YT and YTAD The program has been under continuous development since 1995 HFTA best models horizontally polarized Yagis although a simple horizontal dipole model has been added as well HFTA takes into account the effects of Fresnel horizontal ground reflection coefficients meaning that the ground conductivity and ground dielectric constant are inp
16. cated 260 feet apart we had a 260 foot long dipole between our two towers and into Europe there was rarely much of a difference in reported signal strengths especially given the nature of fast fading on an HF path Page 5 You can enlarge a portion of any HFTA graph using the mouse For example you might want to expand the area from 2 to 15 where most of the action is occurring in Fig 4 Move the mouse cursor to the upper left side of the portion you want to enlarge and hold down the left mouse button While holding down the left button drag the cursor to the lower right and release the left button The graph will instantly blow up to show details in this region To return to the original graph reverse the process at the lower right side of the graph hold down the left button on the mouse and drag it upwards to the left When you release the left button the graph will return to its original area Holding down the right button on the mouse allows you to scroll up and down on the graph You can also choose to expand or contract the X axis for the graph by clicking on the appropriate Max Elev Angle option box on HFTA s main window The default is 0 to 34 You may also choose to change the size of the graph by dragging a corner or by clicking on the Maximize icon at the upper right If you want to read the exact value at some point on one of the curves move the mouse cursor to that point and a Tool Tip will appear giving th
17. d this option MicroDEM will continue to use Save radials as a default value Close the Options dialog and the MicroDEM program Page 34
18. dials en a X Cancel Help Pah Fig A2 Setting up ViewShed Parameters after double clicking a location e Close the Options dialog and then the MicroDEM program to save your options to disk Page 17 Getting Digital Map Data for the USA As mentioned above for the USA the USGS US Geologic Survey maintains two types of public domain terrain data sets on the Internet MicroDEM can use either of these data sets to create terrain profiles for HFTA There are advantages and disadvantages to each method e DEMs Digital Elevation Model are essentially digital versions of the 7 5 minute quad paper topographic maps with which most US hams or hikers are familiar e NEDs National Elevation Dataset are seamless versions of the paper topographic maps USGS DEM MAPS The DEM datasets are available from several commercial vendors Some of these vendors charge no fees for limited Internet access to the data The NED datasets are available directly from US Geological Survey EROS Data Center Sioux Falls SD on the Internet I thank Pete Smith N4ZR for giving me some vital tips on how to download and use NED files Downloading a specific DEM is usually faster than downloading a NED data file because the DEM is generally smaller in size by a factor of about two However you may need to merge as many as four DEMs to cover an area large enough to create terrain profiles around a particular tower location Furthermore
19. e zero position stored in Terrain File 1 This Move Tower function is most useful conceptually when the tower is placed at the edge of a steep drop off but you can also use it to move a terrain feature such as a tall mountain peak farther away from the tower to see how the elevation response is affected See Fig 9 In the Options window click on Move Tower This will open a new window that allows you to specify the distance to move back from the original tower position either in feet or meters This will move the base back the specified distance keeping the elevation the same as the original tower elevation In effect this moves the tower back onto flat land in the direction directly behind the azimuth of interest This is a common situation at the crest of a hill where the land is typically flat so that a house can be situated there Page 9 Options HFTA Options Soil Conductivity mS m Dielectric Units Diffraction Feet Pen Clear YTW DEF C OFF C Meters Move Tower Back Move Tower OK Fig 9 The Options window showing the Move Tower button Once you specify a move distance HFTA requires you to save the modified terrain profile to a new filename The program suggests a filename which you may override if you like For example if the filename in Terrain File 1 is called N6BV 045 00 PRO HFTA will suggest a new filename of N6BV 045 00 1 PRO Whatever filename you choose w
20. e ARRL Antenna Book can create terrain profile files with USGS DEM Digital Elevation Model and NED National Elevation Dataset data but doesn t work with SRTM Shuttle Radar Topographic Mission terrain data See Appendix B for instructions on setting up the Alpha 7 version Dr Guth has modified versions of MicroDEM after June 6 2009 to work correctly with SRTM input You will have to go to the MicroDEM website to download the complete basic package which is about 55 MB in size After you have installed the basic version you must then download the latest executable Microdem exe following instructions also on the site Later versions of Page 15 MicroDEM will work with all DEM NED and SRTM data sets http www usna edu Users oceano pguth website microdemdown htm Once you have installed MicroDEM bring it up on screen Fig A1 is a screen shot of the program with the Windham NH quad map displayed together with Tiger US Census data showing roads highways and streams More on Tiger later J MICRODEM 10 0 build 2009 6 5 1 N42 49 613 W71 17 827 WGS84z 119 5m 392 0 ft BEE Zi micro 8 sescPa TOKON eo BGO Sree 0AM Fig A1l Screen shot from MicroDEM program showing Windham NH region SETTING OPTIONS IN THE LATEST MICRODEM FROM WEB SITE If this is the first time you ve used the MicroDEM program you need to set some options to generate data for HFTA Click on the Options menu listing at the top of t
21. e angle separated by the computed value at that point For example moving the cursor to the top of the 4 bar graph line in Fig 4 will show 4 9 3 meaning that at a 4 elevation angle the statistical percentage is 9 3 from New England to Europe on 20 meters FIGURES OF MERIT In Fig 4 you ll see listed at the right hand side a Fig of Merit for each curve This is a weighted statistical average computed by multiplying the gain at each angle by the statistical percentage that the band is open at that angle The products for all the angles are averaged to compute the Figure of Merit which is calibrated in dBi For example the flatland curve at 70 feet in Fig 4 has a Figure of Merit of 11 3 dBi while the curve for KSMA has a Figure of Merit of 11 9 dBi This means that on average KSMA s signal will be 11 9 11 3 0 6 GB stronger than a flat land station at 70 feet using the same Yagis I should caution you that a Figure of Merit FOM is only a snapshot of a complex situation You can easily find situations where the elevation response of an antenna over complex terrain is better at low elevation angles than another antenna that has a higher FOM over the entire range of possible elevation angles Low angles are especially important during periods of low solar activity when the only possible modes of propagation are low angle modes PLOTTING THE TERRAIN PROFILE Clicking the Plot Terrain button with both KSMA 45 PRO a
22. eas for which you want to download topographic data For example let s download topo data for GM3SEK in southern Scotland His tower is located at 54 44 160 N 4 28 283 W See Fig A11 e Make sure the checkbox labeled Geo Tiff at the lower left is checked e Click on the box for the lower part of the UK e Now click on the button Click here to begin search e Next you ll see a page similar to the one shown in Fig A12 where the area chosen is zoomed in at the right to show some more detail SRTM Data Search Mozilla Firefox File Edit View History Bookmarks Tools Help X ia U Jhttosiportm csi coiar org SELECTIONinputCoord asp L Most visited The CGIAR Consortium for Spatial Information CGIAR CSI 3 Ly Applying GeoSpatial Science for a Sustainable Future Co1ar csi SRTM Data Selection Options 4 Select Server CGIAR CSI USA TelaScience USA HarvestChoice USA sre am king s College UK 2 Data selection method Multiple Select Many tiles can be selected at rando 3 Select File Format Fig A11 Starting page for CGIAR CSI repository for SRTM data Page 28 SRTM Search Results GeoTiff Mozilla Firefox Bile Edit View History Bookmarks Tools Help e SOM ay L http srim csi cgiar org SELECTION istima
23. eep FLAT PRO in terrain filename 4 so they always have a reference flat terrain with which to compare the responses over actual terrains Click on the Cancel button to erase a filename in that Terrain Files box ANTENNA HEIGHTS Once you ve selected a terrain profile name you will want to choose the type of antenna and the number and heights of antennas in a stack Click on the Ant Type or Heights box you want A new dialog box will open See Fig 2 The default when you first start HFTA is one 4 Ele Yagi antenna at 100 feet in height Let s say that you want to specify three 4 Ele Yagi antennas in a stack at 90 60 and 30 feet You would place the cursor in the top left text box and edit the 100 to be 90 Then you would edit the second box to be 60 and the third to be 30 You can move the mouse or use the Tab key to advance the cursor from box to box Once you click on OK you might want to set the same heights for the next Terrain Files box The Copy buttons on the right side of the Height 4 boxes give you a quick way of copying one row to another row Click on the Copy button you want and you will see the other two Copy buttons change their labels to To Click on the To button you want By the way always specify a height for each Terrain 0 feet won t work right Page 2 Enter Heights Antenna Type Terrain BYCAPE45 PRO sEle v K5MA 45 PRO E1e m FLAT PRO 4Ele FLAT PRO Free space gain 2 Ele 5 5 d
24. elimited with commas Character labels are delimited with double quotation marks This sort of data can be imported easily into a spreadsheet or database management software for other types of manipulation if you like Page 10 If you want to print the on screen graphs click the Print button The red trace will be printed with a dotted line to help differentiate it on a black white printer The cyan trace will be printed with a thinner line width to help differentiate it from the other traces Note that if you try to print a full screen graphic parts of it may be cut off towards the edges of the print Resize the graphic to print it fully on your particular printer You could also press the Print Screen key to put a copy of the graph onto the Windows Clipboard This can then be used by another Windows program such as Word for Windows or Paint Shop Pro find Paint Shop Pro to be particularly useful because by selecting Colors Grey Scale I can view the graph as it would be printed on a black white printer To put a copy of only the active window that has Windows focus onto the Clipboard press the keyboard combination Alt Print Screen together Caveats The HFTA program is still under development For validation of its results there are precious little experimental data available showing careful measurements of HF elevation angles versus terrain contours Very few radio amateurs have access to a helicopter to really measure their el
25. evation patterns HFTA does corroborate the results from a helicopter study done by WA3FET and associates some years ago ACCURACY OF TERRAIN DATA The terrain data itself from topographic maps can be sparse or somewhat questionable Irregularities that can be seen with the naked eye from the base of the tower are sometimes not shown on a topo map perhaps because a map was created years ago before things were leveled by bulldozers Furthermore if you are using Shuttle Radar Topographic Mission SRTM terrain data you have to recognize that a radar will see the tops of trees in a dense forest not necessarily seeing the underlying ground And the area behind a steep peak will probably be partially blocked from sight of the Space Shuttle mounted synthetic aperture radar The terrain model used by HFTA assumes that the terrain is represented by flat plates connecting the elevation points in the PRO file with straight lines The model is two dimensional meaning that range and elevation are the only data for a particular azimuth Obviously the real world is three dimensional To get a true picture of the full effects of terrain a terrain model that shows azimuth along with range and elevation point by point would be necessary The computational requirements for such a fully 3 D model even with the detailed terrain data from MicroDEM would be pretty horrendous You can get a feel for how your terrain affects signals launched in vario
26. g 43 MByte in size Once you have downloaded the ZIP file you must unzip the data using a program such as WinZip Fig 10 shows an example of a Windows Explorer screen The filename automatically chosen by USGS imbeds the upper left hand corner latitude and longitude coordinates in it a gO Acer C mapdata p DEMs p n43w072 n43w072 Organize Include in library Share with Burn New folder K Favorites Name i A Date modified Type Size Desktop J floatn43w072_1 fit 1 29 2013 12 19PM FLT File 50 964 KB B Downloads floatn43w072_1 hdr M HDR File 1kB E Recent Places 0 floatn43w072_1 prj 29 2 9PM PRJFile 1kB a SkyDrive E n430072_1_meta htm 312 19PM HTML Document 17 KB E n43w072_1_metaxml 29 9PM XML Document 10KB 5 Libraries n43w072_1as_meta dbf M DBF File 67KB E Documents O n43072_1as_meta shp 29 9PM SHP File 117KB a Music E n43w072_1as_meta shp xml 2 M XML Document ek Pictures O n43072_Las_meta shx 29 2013 12 19 PM SHX File 1KB H Videos _ ned darcsec_f dbf 2 DBF File ned Jarcsec f prj 2 PRJ File 1KB a Homegroup ned_1arcsec_f sbn 2 M SBN File O ned Jarcsec f sbx 2 0 SBX File 1KB jE Computer 0 ned_1arcsec_f shp 2 SHP File amp Acer C E ned tarcsec_fshpxml 2 XML Document Removable Disk O ned arcsec f shx 2 AM SH File a Iomega HDD Bi NED_DataDictionary doc 2 M Microsoft Word 9 STORE N GO K O readmestt 1 29 2013 12 19 PM Text Document iy Network bh 18 items Fig
27. ges asp amp L Most Visited The CGIAR Consortium for Spatial Information CGIAR CSI f i Applying GeoSpatial Science for a Sustainable Future RCH CSIHOME SRTMMAIN E HELP 1 tems have been Found Product SRTM 90m DEM version 4 Data File Name srtm_26_02 zip Mask File Name srtm_mk_36_02 zip Latitude min SoN max 55N Longitude min sw max 0W Center point Latitude 52 50 N Longitude 2 50 W CGIAR CSIHome SRTM 90m Database SRTM Data Processing Methodology SRTM Data Search Disclaimer Contact Us 2004 CGIAR Consortium for Spatial Information CGIAR CSI Fig A12 Detailed view of area selected in Fig A11 e If this is the area you want click on Data Download FTP Save the zipped file to disk probably to the c MapData DEMs subdirectory if you did a standard MicroDEM installation e Use WinZip or the Microsoft Explorer program to extract the TIF file from the zipped file Since each block contains detailed data for 5 of latitude and 5 of longitude each TIF file will be about 70 MB in size e Open MicroDEM and click on File Open Open DEM to select a map Page 29 Creating Azimuth Terrain Files for HFTA in MicroDEM You ve finally managed to generate a digital map using MicroDEM Now yovw ll need your tower s exact latitude and longitude which you ve gotten from a GPS or from Google Earth
28. get an error What you now need to do is to extract from the zip file use WinZip or whatever Page 23 program you want the file with the tif extension into the MapData DEM subdirectory When you open this tif file voila You ll have your topo map open and ready to work on He pit View Favorites Tools Google v she stare Mere Be MMN M Fate 4 ARAL G Artes Under Review ARRL Periodical Active LoTW amp QST The Table SFC E Webinars Wid Wide Ra Cancel All Changes amp Retum to Summary Save Changes amp Retum to Summary Order Options Data Archive Metadata Format _ Format Format Elevation National Elevation Dataset NED 1 Arc Second Geol HTML National Elevation Dataset NED 1 3 Arc Second AE IP HML gt L National Bevation Dataset NED 1 9 Arc Second AcGRID HTML Topographic Change Difference DEM AcGRID ZIP HIML gt Topographic Change NED 2003 DEM AwGRID ZIP HM Topographic Change NLCD 1992 Land Cover AGRID ZIP fum ih Topographic Change Polygons Shapefle ZIP HTML gt E Topographic Change SRTM 2000 DEM AcGRID ZIP HTML gt E National Land Cover Dataset 2001 Canopy Fig A7 Modifying the Data Request for a GeoTIFF output format You can now save your seamless DEM as a DEM with a descriptive name such as your call sign for example and open it directly to be sure it s OK At this point you can delete the
29. h elevation data checkbox they really mean 1 arc second rather than 1 inch Fig A6 Specifying coordinates for NED download Tower is at 42 30 52 96 N latitude and 71 33 0 39 W longitude with 5 minutes subtracted and added to give corner boundaries for data selection box However you decide to calculate the borders now click on Add Area and you will next be asked whether you really want to go on Click OK and you will next be presented with the Summary Request Page Click the Modify Data Request button and the screen shown in Fig A7 will appear Scroll down the page and make sure the National Elevation Dataset NED 1 Arc Second box is checked and that you select GeoTIFF instead of ArcGRID for the Data Format Scroll down to the bottom of the page and click on Save Changes amp Return to Summary button Now you re back at the previous screen but with the required format of the download changed and updated Now click the Download button and follow the instructions to save the zipped file to your hard disk You should write down the name of the zipped file and save it to the subdirectory where you usually place your DEM files For a standard MicroDEM installation that will be in C MapData DEMs We re done with USGS but the fun isn t quite over yet because if you run MicroDEM at this point click File and then Open Open DEM and try to open the zip file you just created you will
30. he main window e Select the Units tab e You probably will want to specify in the Lat Long textbox the exact way you enter or show latitude and longitude For example let s say that your GPS shows your position at 42 4 30 N latitude and 82 7 35 1 W longitude This is the so called degrees minutes seconds method of showing latitude or longitude You would select the Decimal seconds option However if your GPS showed the same position as 42 07500 N and 82 12641 W this is expressed in Decimal degrees Click the OK button when finished e Click on the Coordinates tab In the Verify box click on the option Keyboard entry In the Show roam on all maps box check the Reasonable option Do this also for the Verify Graphical Selections box Click Keyboard selection for target run The values for latitude longitude determined by double clicking the mouse will now bring up a verification box in which you can type the exact coordinates Click the OK button when finished Page 16 e Click on the Views tab and then click the Weapons Fans button Click the LOS and fan algorithm button Make sure that the box labeled Radials from zoom map size is not checked Now click Radial lines discrete Verify Ray Spacing is 5 the default value Click Constant radial spacing and then verify Point Spacing m is 30 meters also the default Click OK to return to the Fan Drawing Options window e Set range rings to show constant
31. i and a 6 element Yagi eR ouput crap arra a E Freq 14 2 MHz HFTA Copyright ARRL 2003 by N6BV Ver 1 40B Max Gain 21 1 dBi N6BV45 PRO 90 60 30 ft Dipole Fig of Merit 10 4 N6BV 45 PRO 90 80 30 ft 2Ele Fig of Merit 13 7 N6BV 45 PRO 90 60 30 ft 3 Ele Fig of Merit 15 2 N6BV 45 PRO 90 60 30 ft 6 Ele Fig of Merit 19 1 Elev Statistic File W1 MA EU PRN Print Out File x a S a 2 3 5 c a i 5 g 2 wW 0 0123 45 6 7 8 9 1011121314 1516 17 1819202122232425 2627 28 2930 31 3233 34 Takeoff Angle Degrees Fig 8 Response for 90 60 30 stacks of different types of antennas Page 8 Options in HFTA From HFTA s main window you can click on the Options button to bring up the Options HFTA form Clicking OFF in the Diffraction box toggles the diffraction mechanism on and off to illustrate the effects of diffraction When diffraction is off you will find that only a reflection analysis is run In general diffractions fills in the holes and knocks down the peaks in an elevation pattern This fuzzing up of the computed response is what happens in the real world where things are rarely very peaky or full of deep holes The drop down box for Soil Conductivity mS m Dielectric allows you to choose the conductivity and dielectric constant of the ground in the foreground of the antenna A conductivity of 5 mS m and a dielectric consta
32. ies for options e You may want to respecify in the Lat Long textbox the exact way to specify or show latitude and longitude For example let s say that your GPS shows your position at 42 4 30 N latitude and 82 7 35 1 W longitude This is the so called degrees minutes seconds method of showing latitude or longitude You would select the Decimal seconds option However if your GPS showed the same position as 42 07500 N and 82 12641 W this is expressed in Decimal degrees e Click on the Coordinates tab In the Verify box click on the option Keyboard entry In the Show roam on all maps box click on the Reasonable option Do this also for the Verify Graphical Selections box The values for latitude longitude determined by the mouse will now bring up a verification box in which you can type the exact coordinates e Now click on the Views tab and then uncheck the box labeled Missing values set to sea level Click the Weapons Fans button to open the Fan Drawing Options page Specify Ray Spacing of 5 and Point Spacing of 30 meters Make sure you click on the Radial lines option in the upper right hand corner See Fig B1 Fan Drawing Options x Curvature TM5 441 how Fan drawing method Radial lines C IHS merge C Radial IHS merge V Symbol at fan location Ray Spacing 5 Point Spacing m 30 v Draw range circles Fans Current Fan S OK X Cancel Help Fig B1 Fan Drawing Op
33. ill automatically be inserted in Terrain File 2 and the height s of the antenna s used for Terrain File 1 will be duplicated for Terrain File 2 This allows you to compare the results for the original and modified terrains directly when you click Compute in the main window So can you actually be too close to the edge of a cliff at least as far as antenna performance is concerned If low elevation angles are needed moving back on a level plain away from the edge of a cliff will probably adversely affect your signals Try it yourself in HFTA HFTA OUTPUT The on screen graphs in Fig 7 or Fig 8 show the elevation response calibrated in dBi from 1 to 34 degrees above the horizon in 4 increments HFTA also writes this data in steps of 1 toa disk file called OUT PRN which is used by the DOS utility program MAKEVOA EXE to create a custom antenna file for VOACAP the sophisticated propagation prediction program Note the MAKEVOA EXE program will only create a VOA CAP antenna file for the first set of data in OUT PRN You may open the OUT PRN file from the graph window by clicking on the Out File button This will open the file using Notepad or whatever program you may have associated in Windows with PRN files You may save the file to another file name if you wish to later use it in say a spreadsheet for your own graphing and analysis Note that a new OUT PRN is created each time you boot up HFTA OUT PRN s elevation data is d
34. iven instructions to open the e mail that will be sent to you automatically when your data is available Page 25 SE 3 setp viewer nationalmap gov viewer USGS TNM 2 0 Viewer x File Edit View Favorites Tools x Google MyMSN 18 SFGate ARRL Articles Under Review ARRL Periodicals Archive ZUSGS 3 Viewer ss cocria Overlays Selection Cart Standard Advanced Annotation Active Tool Download Data cart Pe 2 SAOSGRaE QO Download options 7 Click here to draw and download by t Add items to the cart by using the Download Data tool in f j Topo Imagery the Standard panel S ae Choose a reference area then click c s 7 y T Index 24K X Click on an item in the cart to see the product footprint ere to download by current ma Selected items i Click here to download by coordinate khas E Oy oo Product Type Name Format p s oi National Elevation Dataset 1 arc Current Extent second Pre 71 633 42 417 GridFloat packaged Float 71 468 42 583 lformat Remove selected Checkout R Sia E GursonjPosition422 2 Fig A9 Click the Checkout button When you receive the e mail click on the download link and Save to the specified ZIP file to your usual MicroDEM map subdirectory By default this is C MapData DEMs USGS chooses a one degree by one degree block of data surrounding your station location which can result in files exceedin
35. lick on my merged file N6BV 1 DEM Then I click on the map icon on the top of the merged map s window the one that looks like a miniature map of the southeastern USA I select the file tgr33015 zip in the c mapdata Tiger NH subdirectory and then marvel at what happens SETTING THE REFLECTANCE PARAMETERS MicroDEM defaults to a gray reflectance display for elevation I like to tweak the settings for this by clicking at the top menu Modify Reflectance Sometimes I use a color display of elevations so I may select IHS elev with a Vert Exag of 8 Again Fig Al shows the resulting display for my merged map with Tiger overlay of roads in red and streams in blue Page 32 Appendix B Using the Older Version of MicroDEM SETTING OPTIONS IN THE VERSION OF MICRODEM INCLUDED ON CD ROM Obtaining a completely new version of MicroDEM involves downloading about 60 MB of data on the Internet Some of you are still using dialup service and thus may be limited to using the version of MicroDEM originally included on the CD ROM bundled with the 20 or 21 Editions of The ARRL Antenna Book This limits you to the use of DEM or NED USGS data for the USA Here is how to set up the options in MicroDEM Version 7 0 Alpha the version on The ARRL Antenna Book CD ROM Click on the Options menu listing at the top of the main window e Select the Units tab you may have to use the horizontal scroll arrows at the top to see all the possibilit
36. nd BVCAP45 PRO terrain files selected yields the graph shown in Fig 5 KSMA s tower was located behind his house on a rise about 22 feet higher than my tower s base So his 80 foot high antenna was effectively 32 feet higher than mine This tended to give him an advantage at lower elevation angles as might be expected In addition there was a small peak almost equal in height to the N6BV antenna the red squashed diamond on the left edge of the Y axis This peak tends to limit somewhat the elevation response Note that the Y axis maximum and minimum height values on screen are chosen automatically in HFTA Be careful when making assumptions about the steepness of a terrain Page 6 im Terrain Plot HFTA loj x Terrain Profile BVCAPE45 PRC TO ft K5MA 45 PRO 80 ft 4 000 6 000 8 000 Distance from Tower Base Feet Fig 5 Terrain profile for KSMA and N6BV towards Europe from Cape Cod The squashed blue and red diamonds near the Y axis show the antenna heights My terrain into Japan was another story Fig 6 shows the terrain profile towards 330 the azimuth to Japan About 300 feet away from the N6BV antenna was a small hill with a large water tank on it loj x Terrain Profile K5MA 330 PRO 80 ft BVCAP330 PRO 70 ft 2 000 4 000 6 000 8 000 Distance from Tower Base Feet Fig 6 Terrain profile of KSMA and N6BV toward Japan Indeed this difference was borne out consisten
37. nt of 13 typical of average to better than average ground is the default You will find that changing the ground constants for a horizontally polarized antenna like those used in HFTA changes the elevation pattern only a small amount and only that at very high elevation angles On this page you may select whether to display distances and elevations in feet or meters HFTA saves your choice of feet or meters in a definition file called YTW DEF file so that you don t have to remember the next time it boots up Along with the type of antenna mentioned above YTW DEF also stores your preferred window sizes and locations for the elevation response and terrain plot graphs If HFTA should crash somehow you might end up with a corrupted YTW DEF file You should navigate to the default HFTA subdirectory usually located in the c AntBk20 HFTA subdirectory if you did a standard installation using Windows Explorer and delete the YTW DEF file there or you can erase the YTW DEF file using the Clear YTW DEF button on the Options page MOVING THE TOWER BACK Several years ago Zack W1 VT a prominent VHF UHF expeditioner who is fond of operating from high mountain top locations told me he was concerned that his 6 meter antennas might be too close to the edge of various drop offs to receive the benefit of ground reflections On the Options page of HFTA I have therefore added a function to evaluate the effect of moving the base of a tower backward from th
38. ocation This is where the US Census Bureau Tiger data comes into play Go to the following URL http www census gov geo www fips fips65 and look up the 5 digit FIPS code for your county This file gives a list of the so called FIPS numbers These identify a Tiger file for a particular county in a particular state By the way the term Tiger stands for Topologically Integrated Geographic Encoding and Referencing just in case you were wondering In my case I wanted to download Tiger information for Windham NH where the FIPS number is 33 015 When you have the code you ll only need to do this once go to http www census gov geo www tiger tiger2006se tgr2006se html and find your state at the bottom of the page Click on it and download the appropriate numbered zip file For my old QTH in New Hampshire I chose to download tgr33015 zip to my c mapdata Tiger NH subdirectory Note that I used the Create New Folder to create the NH subdirectory from the basic tree structure MicroDEM created when it was installed Do not try to change the name assigned to this zipped file or MicroDEM will not be able to find and associate it with DEMs you display The internal zipped file structure creates a temporary directory with that number as a name Now you can bring up the map and add Tiger data to it Start MicroDEM and click on the File Open Open DEM selections from the top menu For example I might c
39. of a steep mountainous terrain A CAVEAT ABOUT CLOSELY SPACED YAGIS IN A STACK The internal Yagi model in HFTA is a very simple mathematical model It does not compute interactions between individual Yagis in a stack HFTA assumes that each antenna is a point source For antennas stacked more than about a half wavelength apart this is not a problem For example you should be cautious specifying spacings less than about 20 feet on 20 meters and proportionately scaled on other bands because of mutual coupling effects between real antennas Page 3 Spacings less about 20 feet on 20 meters will show a false increased gain in HFTA even though the real effects of interaction between the beams will actually be to decrease the gain SELECTING AN ELEVATION STATISTICS FILE Click in the box labeled Elevation File to select the nearest elevation statistics file for your targeted receiving area See Fig 3 For example from New England to Europe choose W1 MA EU PRN standing for W1 Massachusetts the Boston area to all of Europe For each amateur HF band from 80 to 10 meters this file shows the percentage of time each elevation angle is effective These statistics were computed for all the times over the 11 year solar cycle when each band is actually open If you run this example you will find that the peak percentage for the 20 meter band is 12 7 occurring at an elevation angle of 5 from Boston to all of Europe Each elevation angle
40. on followed by Merge and then DEMs and Dems pick single e Select the first 30 m DEM filename followed by the second one Click Cancel to end the merge operation Name the resulting file a temporary filename say Merged DEM and get back to the main screen by closing the dialog boxes and the map e Now you need to convert the merged 30 m DEM and the 10 m DEM to DTED files Click on File in the top menu followed by Open Open DEM and select the new Merged DEM file e Click File in the top menu followed by Save DEM and then select the DTED format Make sure that the Lat spacing seconds and Long spacing seconds are set to 3 Click on OK and save to Merged DT1 Again get back to the main screen by closing the dialog boxes and the map e Click on File in the top menu followed by Open Open DEM and select the 10 m DEM file Click File in the top menu followed by Save DEM and then DTED Make sure that the Lat Page 20 spacing seconds and Long spacing seconds are set to 3 for 0 3 seconds Click on OK and save this to a filename such as 10m DT1 Close the dialog boxes and the map e Now you will merge the two DTED files Click on File in the top menu and then click on Data Manipulation followed by Merge and DEMs and then DEMs pick single It may be useful to type DT1 followed by Enter in the Filename box to bring up only the DT1 files you have created e Select fir
41. parated by one foot each For example if you are interested in a single antenna at a height of 80 feet on 14 0 MHz for the KSMA 330 PRO terrain you might first compare three heights of 79 80 and 81 feet bracketing that height The three curves overlaid on each other look relatively smooth except there is a 1 4 dB bump for the 79 foot height Now run three heights of 80 79 and 78 feet Now the curves for 78 and 79 feet look smooth but the 80 foot curve has a noticeable dip This means that spurious artifacts of the ray tracing process are occurring at 80 feet in the program but these would not occur in the real world The solution don t use the 80 foot point in the computer analysis but you would mount your real antenna at that 80 foot height if you like the response at 79 or 81 feet Page 12 FEEDBACK PLEASE I would greatly appreciate feedback from you about this program If you have access to validation data I d surely like to hear about it R Dean Straw N6BV Senior Assistant Technical Editor retired ARRL e mail n6bv arrl net Page 13 Appendix A Preparing a Terrain Data File HFTA needs an ASCII input file with the terrain data in a particular azimuthal direction from the base of your tower Terrain data may be in feet or in meters There are four ways in which you may obtain terrain data and the pros cons for each will be discussed in detail in this Appendix Manually from USGS paper topographic maps
42. shows a typical main window for HFTA Like its stable mates TLW and YW HFTA incorporates a number of Tool Tips When you move the mouse cursor and let it hover over a button or a text box on the screen a brief explanatory note will appear You can select up to four different terrain files each with a set of heights for stacked antennas and HFTA will overlay the resulting elevation patterns on a single high resolution graph I regularly compare any patterns I generate to a reference 3 element Yagi over flat ground usually at a height of 60 feet on 21 or 28 MHz or 100 feet for 14 or 7 MHz These are also the reference antenna heights I specify when using the JONCAP or VOACAP propagation prediction programs HFTA saves the defaults you like to a startup file called YTW DEF If HFTA detects no YTW DEF file on bootup it will automatically create a new one showing blanks for the four terrain files SELECTING A TERRAIN FILE To select a Terrain File click the left mouse button with the mouse cursor in the appropriate text box A dialog box will open up asking you to select existing terrain file from a sorted list of filenames As usual in this familiar common dialog style you may change the subdirectory if you have saved terrain filenames in other than the default subdirectory Keep in mind that you must have a terrain filename showing in the first position in HFTA with blanks in other positions if you like Some operators like to k
43. similar to that shown in Fig A6 For example at K1EA s location in Western Massachusetts his 15 20 meter tower is located at 42 30 52 96 N latitude and 71 33 0 39 W longitude You now have two choices for entering coordinates The most labor intensive one will place the tower exactly in the middle of the resulting NED DEM Convert these to decimal degrees remembering that minutes are 1 60 of a degree and seconds are 1 3600 of a degree 42 30 60 52 96 3600 42 51471 71 33 60 0 39 3600 71 55011 Now add and subtract 0 1 to the tower s position to define the rectangle surrounding the tower base Top latitude 42 61471 Bottom latitude 42 41471 Left longitude 71 65011 Right longitude 71 45011 The second method is easier to do in your head but will result in a slightly offset NED file but one that is still large enough to cover the area around your tower Simply add and subtract 5 minutes to from the latitude and longitude to set the borders You can ignore the values for seconds Following the above example at a tower position of 42 30 52 96 N latitude and 71 33 0 39 W longitude simply make the top border 42 35 N the bottom border 42 25 N the right Page 22 border 71 28 W and the left border 71 38 W See Fig A6 where the Switch to Degrees Minutes Seconds selection has been clicked previously to get to this Download Tool form Note too that I checked the 1 inc
44. st the merged 30 m file Merge DT1 followed by the 10 m file 10m DT1 Click Cancel to exit the merge function and name the file something else perhaps N6BV 1 DEM Now wasn t that fun It sounds very complicated but luckily you won t have to do this very often Again however downloading a NED file may be more efficient Merging Across Different UTM Zones You may live near where two maps you d like to merge are in different UTM Universal Transverse Mercator zones Because of distortions at the edge of any map which after all is converting a round world the Earth to a flat map representation MicroDEM will not allow you to directly merge these two maps across UTM boundaries You use the same basic procedure as above using DTEDs to merge DEMs with 10 m and 30 m spacings rather than trying to merge the DEMs directly For this example we ll merge two DEMs called Dem1 DEM and Dem2 DEM e First convert each DEM to DTED format From the top menu click File Open Open DEM and select Dem1 DEM e Save it as a DTED file by clicking File in the top menu followed by Save DEM and then DTED Make sure that the Lat spacing seconds and Long spacing seconds are set to 3 for 0 3 seconds Click on OK and save this as Dem1 DT1 Close the dialog boxes and the map e Process the second file On the top menu click File Open Open DEM and select Dem2 DEM e Click File in the
45. statistic file is named in the generic format PRN and comes from the CD ROM shipped with the 19th through 21st editions of The ARRL Antenna Book located in the default HFTA subdirectory The Antenna Book s disk contains files for all regions of the USA to Europe EU the Far East JA South America SA South Asia AS Southern Africa AF and the South Pacific OC plus data files for a wide variety of other transmitting sites throughout the world You choose the general area where your transmitter is located during initial installation of the HFTA program Use the installation program for areas other than the ones you ve already installed By the way don t try to select OUT PRN as a statistical date file It won t work Select elevation statistic file My Recent Documents Desktop ry My Documents pE My Computer My Network Places File name Files of type 3 VE1 EU PRN a VE1 JA PRN a VE1 OC PRN a VE1 SA PRN a VE1 US PRN a WO CO AF PRN a WO CO AS PRN a WO CO EU PRN a WO CO JA PRN la WO CO OC PRN a WO CO SA PRN a WO IA AF PRN a WO IA AS PRN a WO IA EU PRN a WO IA JA PRN a WO IA OC PRN wi MA EU PRN E 3 WO IA SA PRN WO MO AF PRN 4a 2 WO MO AS PRN 2 WO MO EU PRN 3 WO MO JA PRN a WO MO OC PRN 3 WO MO SA PRN a WO ND AF PRN 2 WO ND AS PRN a WO ND EU PRN a WO ND JA PRN 2 WO ND OC PRN 2 WO ND SA PRN 2 W1 MA AF PRN a
46. t 3 Ele Fig of Merit 11 3 K5MA 45 PRO 80 ft 3 Ele Fig of Merit 11 9 FLAT PRO 100 ft 3 Ele Fig of Merit 10 4 FLAT PRO 70 ft 3 Ele Fig of Merit 10 4 Elev Statistic W1 MA EU PRN Print Out File Close Gain dBi Elevation Statistic i 0 2 4 6 8 1012 14 16 18 20 22 24 26 28 30 32 34 Takeoff Angle Degrees uwo Oeae NW ANONG Fig 4 Comparing responses for KSMA and N6BV on Cape Cod Plotted on the same graph in Fig 4 as the line graph elevation responses is a bar chart showing the statistical elevation angle percentages versus elevation angle These percentages are valid for all the times the 14 MHz band is open from New England to Europe The degree to which the antennas chosen for a particular terrain cover all these angles the more effective will be those antennas terrain for all periods of the solar cycle The ideal coverage would be a high gain rectangular shaped elevation response from 1 to 28 the full range of elevation angles covered on this band to Europe In Fig 4 you can see that KSMA had an advantage of as much as about 5 dB into Europe for angles less than about 10 but that my station next door had a slight advantage for slightly higher takeoff angles Still the N6BV terrain and 70 foot high antenna performed as well or even better than a station with a 70 foot high Yagi located over flat ground the fourth cyan curve Both antennas were physically lo
47. tions Make sure you click the Radial lines selection Page 33 e You may next want to set a range ring to show the circle surrounding your tower location I recommend that you use a radius of 4400 meters Use Options Views O Range circles and then type 4400 for the first range ring 2200 for the second and zero for the others Note that if you have selected feet for your units this entry must still be 4400 meters despite the label of feet that shows on screen Yes this is a bit confusing e Set the default subdirectories by clicking the Directories tab MicroDEM creates a subdirectory system where map data will be stored usually in x Mapdata where the x denotes the disk drive you select during installation The radial PRO files you will be creating later will be stored in the x Mapdata MD PROJ Fans subdirectory e Next click on the Weapons fan icon or click Calculate Intervisibility and Viewshed and double click anywhere on the map A box will appear into which you type in the exact latitude and longitude then click OK ViewShed Parameters Fan name Viewer range m Viewer AGL m Viewed point AGL m Left boundary fo Right boundary 355 OK C l 9 Haln dain Fig B2 After you double click the map in the Weapons fan process this box will appear after you key in the exact latitude and longitude and click OK Make sure that the Save radials checkbox is checked Once you have selecte
48. tly when we compared signals to Japan See Fig 7 Since we couldn t co exist operating the same DX contest because of our proximity to each other Jan and I would alternate contests He would operate one weekend and I would operate the Page 7 next contest weekend We ran a coax between our houses so that we could use each other s antennas Even with an extra 400 feet of coax between the antennas KSMA s antenna terrain was always superior to my shot into Japan Output Graph HFTA xi REENE S Freq 21 2 MHz HFTA Copyright ARRL 2003 2004 by N6BV Ver 1 03 Max Gain 15 3 dBi epy Eee d BVCAP330 PRO 70ft 3 Ele Fig of Merit 8 2 K5MA 330 PRO 80 ft 3 Ele Fig of Merit 12 1 FLAT PRO 100 ft 3 Ele Fig of Merit 10 2 FLAT PRO 70 ft 3 Ele Fig of Merit 9 2 Elev Statistic W1 MA JA PRN Print Out File Close Elevation Statistic thot tt ove ote ee ae oae O N ANONG 01234567 8 9 1011121314 151617 18 19 20 Takeoff Angle Degrees Fig 7 Graph for K5MA and N6BV towards Japan from Cape Cod on 21 2 MHz DIFFERENT TYPES OF YAGIS As mentioned earlier you can select the type of antenna that HFTA uses for individual terrain profiles Fig 8 shows how different types of antennas affect the far field elevation response at the N6BV station in Windham NH in the direction of Europe for four different stacked antennas at 90 60 30 feet a dipole a 2 element Yagi a 3 element Yag
49. tower was located near the junction of two topographic maps In MicroDEM first make sure that you close any open DEMs e Click on File in the top menu and then click on Data Manipulation followed by Merge and then DEMs Click on Dems pick single and you will be presented with a list of the DEMs located in your default maps subdirectory Select the first DEM you want followed by the second one you wish to merge In my case I selected the Windham NH and then the Derry NH quads e Then click Cancel to end the merging operation and save the resulting merged file using an appropriate filename such as Merged Windham_Derry DEM or perhaps N6BV DEM Finally close the merge operation by clicking on File and then Close Merging 10 m and 30 m DEMs Most USGS DEMs are 30 meter DEMs meaning that the internal data is sampled at 30 meter horizontal intervals Some of the newer DEMs however are sampled at 10 meter intervals MicroDEM won t allow you to merge these two different types directly There is a workaround involving creating intermediate merged data files using the DTED format At this point however you may well want to consider downloading a NED data file rather than working with multiple DEMs with different resolutions However if you choose to stick with DEMs here s the method to merge say two 30 m DEMs and a 10 m DEM e With no map showing on screen click on File in the top menu and then click on Data Manipulati
50. us azimuthal directions by using separate data files for these directions For example from my old QTH in New Hampshire my coverage to central Europe goes from about 30 to 60 I have thus evaluated azimuth shots for 5 increments 30 35 40 45 50 55 and 60 The overall effect for four azimuths for a single antenna height can be plotted together on one screen to visualize the effect of azimuth and thus terrain shape However I will often plot the response of three real world Page 11 azimuths plus a flat ground case This way I can judge what happens with changes in terrain shape compared to the result due only to the height over flat ground I had mentioned earlier that the internal mathematical model of an antenna is very simple and does not take into account mutual impedances between antennas in a stack There is another simplifying assumption made inside HFTA ray tracing is only done in the forward direction from the tower towards the ionosphere on a single azimuthal heading In earlier versions of this program YT and YTAD I specifically limited the choices of antennas to directional antennas that had little gain in the backwards direction In HFTA I ve included a simple dipole model so that users can assess their own situations better But the same program restrictions occur ray tracing is still only done in the forward direction despite the fact that a dipole is bidirectional WHAT ABOUT DISTANT MOU
51. uts to the program through the Options subscreen You will find that these ground coefficients have only a minor effect on the elevation pattern at low angles gradually becoming more significant at higher elevation angles Besides reflection HFTA also takes into account diffraction Please note HFTA does not work with vertical polarization only horizontal and it works best with directive arrays such as horizontally polarized Yagis or quads iil HFTA HF Terrain Assessment HFTA HF Terrain Assessment ai Version 1 04 Copyright 2003 2004 ARRL by N6BV Mar 02 2004 Frequency Diffraction ON 142 MHz Options Terrain Files Ant Type Heights BVCAPE45 PRO 3 Ele 70 feet IV Terrain 1 K5MA 45 PRO 3 Ele 80 feet I Terrain2 M Show Ants 1 2 a FlaTPRO aee 100 feet temaina af FaRo ate 70 feet f terang lot Terrain Elevation File Max Elev Angle Elevation file W1 MA EU PRN C 20 deg C 25 deg 34 deg Fig 1 HFTA main screen Page 1 HFTA s output response is referenced to an isotropic radiator in free space that is in dBi The free space gain assumed for the default four element Yagi model is 8 5 dBi Fig 1 shows HFTA s main window We ll get into details about operating HFTA later but first we need to look at the terrain data files you will need for your particular location Instructions for Running HFTA Start up HFTA by clicking on its icon Look again at Fig 1 which
52. w Area button and choose Elevation data from the next list Now click the Next button to bring up the USGS Available Data for download screen Check National Elevation Dataset 1 arc second Pre packaged Float format otherwise known as GridFloat Do not check the 1 3 arc second format unless you want to download some huge files with that unnecessary amount of resolution USGS Available Data for download Use the checkboxes to select specific format of products you want under each theme Click on the products to preview their footprints on the map Products will be added to the Cart on the left side of the screen Elevation 4 products Product x Pre packaged Float format Pre packaged ArcGrid format Pre packaged Float format Date National Elevation Dataset 1 arc second Best Available National Elevation Dataset 1 arc second Best Available National Elevation Dataset 1 3 arc second Best Available National Elevation Dataset 1 3 arc second Best Resolution 1 arc second 1 arc second 1 3 arc second Type Format Metadata Staged GridFloat Staged ArcGrid Staged GridFloat Fig A8 Choose GridFloat data format Click Next again to bring up your shopping Cart on the left side of the screen and click the Checkout button You will be asked to provide your e mail address twice and then you can click Place Order Yov ll be g
53. your own tower s base entering at each point along a desired azimuthal direction the distance from the base and the elevation at that point into a disk file For some parts of the world where digital terrain data isn t available on the Internet using a paper topographic map may be your only choice If you examine the contents of a sample file using an ASCII word processor you will find that the data are arranged in two columns separated by a tab space or comma Each line is terminated with a carriage return linefeed and each line represents a single point For example to evaluate my terrain towards Europe from my old location in New Hampshire I drew a line from the base of my tower at an azimuth of 45 towards the center of Europe Where this line crossed each contour on the topographic chart I measured the distance from the tower base and entered it into the disk file Here is a sample of a typical data set I generated manually Page 14 feet 0 430 200 420 500 410 700 400 800 380 900 360 1000 340 1550 360 2200 340 4800 340 13200 360 The first data line starts at the base of the tower at 0 feet distance The elevation height above mean sea level also known as ASL standing for Above Sea Level at my old tower base was 430 feet The next line in the data files shows that 200 feet from the tower base the elevation is 420 feet at 500 feet the elevation is 410 feet etc I entered data at distances from the tower for more than
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