LP-200 Assembly & Operations Manual Rev. 1.6
Contents
1. N8LP LP 200 Dummy Load Wattmeter Assembly and User Manual Copyright 2006 TelePost Inc 2 LP 200 Assembly amp Operations Manual Rev 1 6 1 Introduction LP 200 Assembly and Operations Manual TelePost Inc c 2005 2006 Manual Revision 1 6 2006 Your company Introduction 3 11 Assembly U1 U2 U3 U4 U5 U6 L1 3 SW1 3 C1 2 7 17 C3 5 10 19 C4 C9 12 18 21 C6 13 14 C11 16 20 22 C8 15 D1 D2 D3 D4 D5 7 9 Q1 Q2 4 LCD1 J1 J2 J4 J5 Y1 R1 10 H2 6 R11 33 H3 R4 R5 H7 34 38 H8 H9 R12 13 39 8 R15 32 R14 35 37 R36 40 T1 5 1 Fan amp guard TO 220 Heat sink PCB Bottom plate 2 pin header 3 Jumpers 2 8 pin sockets 14 pin socket 28 pin socket 16 pin LCD header DC power pigtail w connector 2 4 40 x 1 4 screws 4 40 x 3 4 screws 4 40 x 1 2 hex spacers 2 56 x 1 4 screws 2 56 x 1 2 spacers LP 200 Parts List 16F876 LM7805T MCP3302 TLC271ACP LM34DZ MAX6250 1 mH choke Tactile Switches 6mm 0 1 uF marked 104 only three supplied for 30W version 10 uF 0 33 uF marked 334 1 uF marked 105 0 01 uF marked 103 2 lead spacing 0 01 uF marked 103 1 lead spacing 330 pF marked 331 1N4148 small glass pkg LED 1N4001 larger black pkg HSMS 2805 Schottky dual diode SMD 1N5711 small glass pkg only three supplied for 30W version 2N7000 not supplied for 30W version 2N39042. The LCD could get scratched if installed early even though it has a protective covering The fan needs to be mounted before it is soldered to the PCB This is done after initial setup Limit new parts to a handful at a time to make it easier to trim the pigtails There is a mistake in the silkscreening for C4 which shows it as an electrolytic when obviously it isn t There is also a silk screening mistake on the position of Q2 it s actually below and slightly left of U4 Also C21 is mounted under the PCB NOTE Newer boards have corrected some of these problems and eliminated the components under the board Without the added bypass cap the temp display flickers a little at high power You will have to scrape a little of the solder mask away under the board to make room for C21 Its leads should be as short as possible with one lead going to U3 pin 1 and the other to ground You can use the silk screened part values for the location of most parts If you are unsure about a part s location or have difficulty reading the silk screen refer to the artwork above Some of the resistors in the area of the preamp limiter will need to be mounted vertically to fit When installing the dummy load resistors you need to place a flat object under each resistor to provide the correct spacing from the board A scrap of 1 16 PCB material will work well or a popsicle stick After the resistors are installed it is necessary to install U5 the temperature sens
3. 1602 LCD Socket DC jack BNC jack 10 pos programming header 20 MHz resonator 1M 1 8W 1 Br BI Bl yel 10k 1 8W 5 Br Bl Or 10k 1 8W 1 390 1 AW Or Wh Br 110 3 AW 1 Br Br BI BI 22k 1 8W Rd Rd Or 20k pot 150k 196 Br Gr Bl Or 1k 1 8W 5 100 3W 5 270 1 4W Rd Viol Br 47 1 8W Yel Viol Bl FT50 61 Power Switch not supplied for 30W version mounts on LCD board only 8 supplied for 30W version not supplied for 30W version 4 40 x 1 2 round spacers not supplied for 30W version 2006 Your company LP 200 Assembly amp Operations Manual Rev 1 6 o t t eh es 15 Di N LP LPPBHS 1 4 R3 c Bees De TelePast tne Before starting assembly of the LP 200 you should check the parts bags against the parts list above Be careful when opening the bags to make sure that no parts are lost It is a good idea to open the parts bags over a shallow cardboard box lid like that of a shoebox or shirt box This will ensure that you won t be looking around on a cluttered counter or the floor for missing parts It is a good idea to read through these assembly instructions before starting Be especially careful of D4 the HSMS 2805 dual Schottky diode chip which is a small SMD part It is packaged in a little plastic blister pack and taped to a piece of paper
4. A 15W soldering iron with a small tip will be best for most of the assembly along with thin diameter solder You will also need a small needlenose pliers diagonal cutters small Phillips and slotted screwdrivers and a small wrench To install the HSMS 2805 will also require eye magnification This can be in the form of magnifying eyewear or a magnifying worklight If you don t have these an inexpensive pair of reading glasses from the local pharmacy would make an adequate substitute Look for a pair with a diopter rating of 2 or 3 A small roll of solder wick might also come in handy when installing the HSMS 2805 The only difficult part to install will be the HSMS 2805 but if you plan ahead and work slowly and carefully you should not have a problem with this part There are a number of tutorials on the web to help with SMD part installation Since this part has relatively wide pin spacing for a SMD part find the following process to be effective Here s a method use that works well Carefully place the SMD part over the pads making sure that it is lined up properly One pin is wider and closer spaced than the other three Match the device to the silkscreen layout 2006 Your company Introduction 5 4 3 It will take a little practice to get the part placed correctly while holding it in place The best tool for this is a good pair of non magnetized tweezers You can also use a small non magnetized screwdri
5. that the correction diode is dc biased while the detector diode is ac biased The uncorrected errors are within about 796 down to 1 milliwatt These errors are easily corrected in software 2006 Your company Introduction 9 The output of the detector is fed to two A D inputs with 12 bit resolution By feeding one A D input with a direct feed and the other through a 2 1 voltage divider have two simultaneous samples to choose from with a 4 1 difference in power which can choose between for an auto ranging display This gives me higher sensitivity at low power levels while still providing high power capability Another A D input is fed from a temperature sensor to allow for temperature correction The 12 bit A D converter connects to the PIC microcontroller through the serial interface The frequency is sampled at very low power through a 1k resistor bridging the 52 5 ohm load across the current sampling transformer A three stage pre amplifier limiter provides about 40 dB gain allowing the frequency counter to work down to 1 mW input It is important that the correct frequency be known at all times for the proper correction factor to be applied The accuracy of the counter is about 596 due to the use of a ceramic resonator for the PIC clock This is more than adequate for the correction routine but may provide a frequency display that appears to be 1 MHz in error near the band edges This is normal Th
6. two because of the normal A D error and decreased resolution of the higher power input 2006 Your company LP 200 Assembly amp Operations Manual Rev 1 6 1 3 This is the end of the normal setup procedure The adjustments will be saved in non volatile memory You can now mount the fan to the standoffs using the 4 40 x 3 4 screws The fan is installed with the metallic hub facing upwards as opposed to the printed label and with the fan guard on top as shown in the picture The red wire goes in the left hole and the black wire goes into the right hole when looking from the front of the PCB You should be able to solder these from the top of the PCB but if you wish you can remove the bottom plate and solder from underneath Circuit Description You should refer to the schematic for circuit details The LP 200 is a combination dummy load and wattmeter The dummy load is made up of eighteen 100 ohm 3W 596 resistors for an inherent dissipation rating of 54W A variable speed fan is provided to extend the power rating 100W continous The input BNC connector connects directly to this load through a current sampling transformer On average the eighteen resistors should have a combined error of about 296 maximum This results in an SWR of about 1 02 1 at low frequencies Stray coupling and lead inductance causes the SWR to rise with frequency but it is still under 1 1 1 at 54 mhz The current sampling transform
7. without any ICs or the LCD installed Apply 12 14V to the power jack the wire with the white stripe on it is the positive lead Turn the power switch on up The LED should light and you should measure 5V at the output of the 7805 regulator If all is well disconnect the power and install the PIC chip and LCD Be careful to install the PIC with the right orientation and to line up the pins of the LCD plug with the socket Set R8 to midrange and reconnect power You should see the splash screen for a couple seconds as shown below followed by the main screen If you do not see it try adjusting R8 until you see the screen and then adjust for a pleasing contrast ratio If you don t see the splash screen refer to the Troubleshooting section If all is well then turn power off again and install the other ICs being careful to check orientation as you do Power up again You should see the main power screen below although the power reading should be zero the temp should read near 072 degrees F and the load will show 50 0 The center and right buttons below the LCD are used to input values using an Dn Up scheme On the main screen they allow you to switch between degrees F and C NOTE The main screen was changed so that now Freq is displayed instead of Load If all is well to this point apply a little power from your transmitter You should see a power reading of roughly the correct value If this is the case then you are ready
8. 00 mHz see graphs below Continuous Power Rating 30W 100W with variable speed fan option Display Resolution 001W to 1W depending on scale Frequency counter accuracy 596 Dual range with auto ranging Displays power temperature degrees C or F and frequency on main screen Temperature compensated over load operating range of 65 125F 18 52C see graph below 16x2 LCD with selectable backlight Precision A D voltage reference 02 12 bit A D converter Five separate calibration screens Power Input 10 14 VDC LP 200 Pwr vs Temp Power vs Temperature 2006 Your company 12 LP 200 Assembly amp Operations Manual Rev 1 6 Z R 100 0 REF 50 U START 2 Z R 100 0 REF 50 START 2 Load resistance at 70 deg F Load Resistance at 125 deg F Frequency scale is 2 54 mHz Vertical scale is 1 ohms div centered on 50 ohms 2006 Your company
9. Dn or Up buttons to set the cold resistance value to match the reading you measured Step forward to the Load Hot screen and enter the hot value you measured at 125 F 52 C Next step to the V Offset screen If the Volts display is reading higher than 0 000 use the Dn button to adjust it to zero This adjustment correctsm for any positive offset error in the op amp input If the reading is 0 000 to start with you may still have a negative offset error To check this apply minimum power from your xmtr You should see a reading of 500 volts or lower Using a DVM monitoring pin 2 of U3 adjust the voltage on the V Offset screen to match the DVM reading using the Up Dn buttons It should require an adjustment of 10 mv The next CAL screen is an overall gain setting This can be used to match your LP 200 an external meter if you have a professional model available for comparison The gain steps are 25 each Once again the Up Dn buttons are used to increment or decrement the steps The last CAL screen sets the gain on the high power scale to match that of the low power scale This adjusts out any errors in the resistive divider feeding the A D input for the high power scale Apply a signal of 10 20 W and use the Up Dn buttons to adjust the reading of the V high A D input to match the V low 2 number which takes the more sensitive low power A D input value and divides it by two in software There may be a 2 3 bit difference between the
10. e rest of the work is done in software where the necessary calculations are made and the display is formatted All correction factors are stored in non volatile memory to ensure that the meter always boots up with the correct CAL constants You may want to tape a little piece of paper under the bottom plate with the correction values and Load resistances in case you ever have to replace the PIC A 10 pin programming port is provided to allow for software updates in the future and is normally jumpered out of the circuit 1 4 Schematic Schematic 2006 Your company 10 LP 200 Assembly amp Operations Manual Rev 1 6 ariu Progeanner Fart i ape UL 16 154149 11 RLS Lk D Me El osce CLKOUr T REesanabar i I 18 f ae m Rri TLOSL CCPB 105211 RIESTPL HB LT D v T 1 5211 NIE i v RS di iB Pa Ae Sey GL ig i4udc 22 A In a sd IMP Coating Fan 33 2 4 ia X ne e S gh Da gv uua Power Jak V yt m 1 5 Troubleshooting This section is a work in progress In case of difficulty contact me at larry telepostinc com or via phone at 734 455 3716 2006 Your company Introduction 11 16 Specifications Features amp Specifications SWR 1 1 1 from 2 30 mhz 1 3 1 to 1
11. er uses 11 turns and is terminated with a pair of 110 ohm 196 resistors in parallel Also connected to this point is a 1k resistor which provides a feed to the frequency counter circuit The parallel combination of the two resistors and the input resistance of the counter preamp results in a load of about 50 ohms Variations in the combined Z of the two resistors and preamp are calibrated out with a frequency ependent software correction routine The sampled current is applied across this 50 ohm load to provide a voltage that is proportional to the input voltage At the maximum rated input power of 120W this voltage is approximately 110 Vpeak 11 2 10 Vpeak The signal at this point feeds a diode detector which in turn feeds an op amp correction circuit The op amp circuit was originally designed by KIGWX John Grebenkemper and was used in his Tandem Match article from recent ARRL Antenna Books He originally described this circuit in an article in the August 1990 QEX issue This circuit provides reasonably accurate correction for the diode forward voltage drop if the diodes are carefully chosen In a departure from the original articles and in an effort to eliminate the need to match diodes am using Agilent dual Schottky diodes on a common substrate in a single package The dual diodes eliminate the need for diode matching and have the added advantage of matched temperature coefficient There are some small remaining errors caused by the fact
12. or 05 should be bent so that it touches R26 If you have it a dab of heat sink compound will ensure a good heat transfer to the sensor but is not necessary if care is taken to make sure U5 touches R26 The three jumpers are used at J5 and SW5 J5 is the programming port and the LCD data is looped through this header Jumpers need to be installed between pins 3 amp 4 and 5 amp 6 otherwise the LCD will not work For reference pins 1 amp 2 are on the end closest to the contrast pot The third jumper is used at SW5 to enable the LCD backlight When in place the backlight is on If you don t want to use the backlight just install the jumper on only one pin so that it doesn t get lost The backlight draws about 200ma so it makes a big difference in power draw especially with the 30W non fan version of the load Once all the components are installed you can mount the hardware This includes four 4 40 x 1 2 standoffs for the fan round four 4 40 x 1 2 standoffs for the underside of the board hex and two 2 56 x 1 2 standoffs for the LCD display The standoffs for the LCD should use lockwashers between the board and the standoff to raise the LCD to the correct level to match the height of the connector 2006 Your company LP 200 Assembly amp Operations Manual Rev 1 6 1 2 They are installed on between the PCB and spacers on the end of the LCD furthest away from the socket Lockwashers should also be used for
13. the screws under the fan to avoid being loosened by vibration Next wind the toroid with 11 turns of the enameled wire supplied with the kit The toroid should be wound over about 909 of the core with the ends coming off on the correct sides to easily connect to the holes in the silk screening A turn is defined as the wire passing through the core If you count only the turns on the outside of the core it will look like 10 turns Leave about 3 4 of lead at the ends ocrape about 1 2 of insulation off the ends of the wires pull the ends through the holes until the core is tight to the board and then solder the leads in place Trim the small piece of hookup wire to about 3 4 and strip about 1 8 of insulation off the ends Form the wire into a U shape and feed through the toroid Insert the ends into the holes in the stripline traces on either side of the core and then solder in place Make sure the wire is tight and holds the core against the board You ll notice that we haven t installed the fan yet This is because calibration will be easier without the fan installed because of better access to the load connections to allow easy measuring of the DC resistance of the load and also because it will be easier to reach 125 degrees F to measure the hot load resistance Before applying power to the board you should mount it to the bottom plate to prevent accidental shorts to stray wire or parts on the bench Initial checkout should be done
14. to continue to the Setup section Setup The main purpose of the setup procedure is to calibrate your load at normal and hot temperatures to correct for any op amp offset error and to set the overall gain if necessary and the relative gain between the low and high power inputs Pressing the left most switch button below the LCD display will cycle you through the CAL modes in 2006 Your company Introduction 7 the following order Main CAL Load Cold CAL Load Hot CAL Offset CAL Gain CAL Hi Lo gain matching The mode cycles back to the beginning after the last CAL screen Before adjusting the CAL screens you need to make a couple of measurements First measure the DC resistance of the dummy load Load Cold by placing probes from a DVM on the ground and top sides of the resistor bank at room temperature about 70 F 21 C It should measure close to 50 0 ohms Check the resistance of your probes by touching them together If there is any residual resistance from the probes this must be subtracted from the measured value of the load With the probes not connected apply 10 20W of power to the dummy load Watch the temp display and when it reaches 130 F 54 C turn off the transmitter and disconnect it from the LP 200 Measure the hot load resistance Load Hot of the resistor bank as the temperature drops to 125 F 52 C Using the mode button step to the Load Cold screen and use the
15. ver for this or a sharp object like a safety pin bent to allow easy manipulation There is a design floating around the web for a hands free holder which uses a safety pin gum eraser and small weight This allows you to hold the solder and iron with your free hands find that once you have the part properly placed you can hold it in place with one hand and tack one pin down to the tinned pad below it Once the one pin has been tacked in place you can solder the other three allowing a very small amount of solder to flow between the pin and pad Once these three pins are solidly soldered you can go back and touch up the first pin Clean the tip after soldering each pin and work slowly If you get too much solder on a pin or bridge two pins you can use small SolderWick to clean it up Let the part cool after extended application of the soldering iron These parts are much more robust than you might think but why risk damage would install the HSMS 2805 first to allow unrestricted access to the pads Next would install the SOCkets 5 easier to get them installed flat against the board before any other parts are installed Next would install the tactile switches for the same reason The rest of the parts can be installed in any order you like but would save the 7805T regulator LCD T1 toroidal xfmr and fan for last The 7805T is tall and could easily get bent during installation of other parts otherwise as is also the case with T1
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