Autek QF-1A User Manual
Contents
1. Signal A flat response is approximated with the Aux Notch at 11 000 and main filter as follows PEAK Freq 12 o clock Sel Min NOTCH Freq 2500 Sel Max LOWPASS Freq 2500 Sel Min HIGHPASS Freq 250 Sel 2 o clock Note Even with these settings the filter contains additional fixed rolloffs below 250 Hz and above 2500 Hz so is not intended for Hi Fi applications only communications TTY SSTV and Misc For TTY SSTV etc reject low frequencies using HIGHPASS Sel and Freq about 10 12 o clock experiment Or use notches to reject CW etc You will no doubt discover other settings for voice CW etc not in this table but useful under some conditions or with your own ear preferences There is a conceivable use for almost all of the infinite number of settings under some conditions and with some signals Line Noise Ignition or Other Static The QF 1A will produce some improvement due to narrower bandwidth especially on CW but nothing dramatic on voice The only really good solutions are a good IF NOISE BLANKER in your receiver or a beam antenna Even IF blankers are generally ineffective except on car ignition noise and may help a little on line noise Audio NOISE LIMITERS not to be confused with IF BLANKERS can be built for the cost of two 5 cent diodes see Radio Amateur s Handbook but we found them to cause distortion and be virtually worthless for noise so th2. desired CW signal comes through C USEFUL ADJUSTMENTS See Tables 1 and 2 D IN CASE OF TROUBLE We carefully test all filters Most problems occur when first used due to improper connection read instructions again or misunderstanding of operation The following are most common HUM OR DISTORTION WHEN USING HEADPHONES Hum generated in the QF 1A is normally barely audible with a speaker unless you place your ear within a few inches of the speaker However hum and distortion may be troublesome if you use 4 8 ohm Hi Fi headphones which are much too sensitive To cure this and improve Hi Fi listening as well connect a 47 ohm resistor in series with this type of headphones HUM WITH SPEAKER Usually this comes from your receiver The QF 1A loads the receiver output much less than a speaker or phones Therefore you may find that switching the filter on produces hum although no hum is heard in the filter off bypass position This may simply be because the filter is not loading down the receiver as much To see if the filter is really causing the hum pull the filter input jack out of your receiver not the same as switching to bypass If the hum goes away or is reduced to nothing with the filter input jack lying on the table then the hum is coming from the receiver and being emphasized because of the light loading by the filter input Several solutions are indicated 1 Check for good contact b
3. with the main freq control Then adjust the trim pot for max response Readjust the main freq and trimpot for max response Repeat until no further improvement in response is noted Note Alignment is the responsibility of the owner even if needed during warranty Our minimum 17 00 service charge applies to any return simply requiring alignment H LATE NOTES If you wish the QF 1A to drive a speaker in bypass you must obviously connect the QF 1A input to a rig output which is capable of driving a speaker Some headphone outputs but not all can drive a speaker When the filter is on virtually any high level rig output can drive it However in bypass the rig s output is connected directly to the QF 1A output jack so the rig must be capable of driving the speaker if any connected to the QF 1A output The QF 1A has proved to be extremely reliable Despite a 1 year warranty we ve had periods of up to 3 months where not a single unit has failed on return However we emphasize that MOST RETURNS have nothing wrong with them Please be sure there is a problem before any return RF pickup seems to have been virtually eliminated However approximately every 4 months someone reports RFI If pickup should occur we emphasize again that there is nothing wrong with your unit and any problem must be solved in your shack See In case of trouble Reports are that all owners have been successful usually
4. INSTRUCTIONS QF 1A AUDIO FILTER Your new audio filter is the product of several years of development by the originator of commercial active audio filters for shortwave communications 1972 Each filter is thoroughly tested twice before shipment Please read the instructions carefully for best results and save them for future reference If you require adaptors or other parts not supplied please obtain these locally as we do not stock them A INITIAL HOOKUP Plug the QF 1A into your receiver s phone jack or speaker output Any impedance is O K Obtain an adaptor if size is not compatible Connect any impedance phones or speaker to the rear panel phone jack output To avoid hum or distortion with Hi Fi headphones use a series resistor of about 46 ohms See In case of trouble The filter input may also be connected to the revr speaker wires Just be sure the input cable shield connected to QF 1A chassis is connected to the grounded speaker wire otherwise there may be hum Note This is rare but some Barlow Wadley radios and CB sets require a load resistor across their speaker or phone output for a DC return The filter s high input impedance does not provide this Try a resistor in the range of 10 to 100 ohms installed in the radio across the output being used Otherwise the set may appear to be dead as the output stage bias is wrong B FAMILIARIZATION The filter selects or rejects certain frequency
5. TERY OPERATION DESIRED Locate the rectifier diodes D1 and D2 on the schematic These are directly forward of the right transformer screw as viewed from the front of the unit Connect 12 to 14 VDC to the right side of either diode the side with the band on the diode Connect the battery ground to the filter chassis ground Note reversal of battery polarity even for an instant will burn out the filter not covered by warranty Table 1 USEFUL ADJUSTMENTS Your QF A can imitate the response of virtually any filter with fixed responses at any price and give an infinite number of other useful responses as well Truly if the QF 1A can t pull the signal out no other filter can either However the QF 1A s flexibility means that even experienced operators will need some time to learn how to best use all the controls The following table will aid you IMPORTANT Don t give up on a setting because it doesn t seem to help Tomorrow with different conditions this setting may turn out to be just what s needed Condition Useful Adjustments See Note 1 for Aux Notch setting Desired CW Signal PEAK Casually listen with 7 to 10 o clock selectivity yielding a relatively wide 80 to 120 Hz bandwidth Adjust frequency for desired CW note Gradually increase selectivity and touch up frequency to match conditions There is much confusion among hams about ringing of a CW filter mainly caused by mtrs of filters w
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7. ches a few hundred Hz at the highest frequency setting 2500 Hz This bandwidth increase is deliberate and makes for easiest tuning At min Sel the filter is almost flat In NOTCH and LOWPASS the panel suggests the best settings More selectivity rotation clockwise makes the notch narrower and shallower hence harder to tune in LOWPASS and HIGHPASS excessive selectivity rotation can lead to ringing at some frequencies The ideal theoretical best selectivity for least peaking in LOWPASS and HIGHPASS occurs when the selectivity control is rotated about two thirds the frequency control i e if the frequency control is rotated 50 rotate the selectivity control about 30 However this rule of thumb should be broken under many conditions see Tables 1 and 2 4 Frequency Control This tunes the main filter frequency from about 250 to 2500 Hz the entire usable communications range for voice CW and digital RTTY SSTV etc signals 5 In Out Switch This turns off the AC power and bypasses the filter There is an unavoidable click when thrown due to the power supply charging or discharging The filter draws less than 1 2 watt if left on accidentally Note Volume is adjusted with your receiver s gain control Gain at high selectivity in PEAK and LP is high and very little noise comes through so keep receiver gain low under these conditions to avoid saturation of the QF 1A power amp distortion when the
8. components of signals you tune in This allows it to reject undesired signals such as noise and interference while passing the desired signal so long as the noise and signal are not on the same frequency This frequency selection rejection is optimized with 5 controls 1 Auxiliary Notch Frequency A notch rejects a narrow band of frequencies such as a whistle or a code station The Aux Notch is present at all times To effectively disable it set it to either 80 or 11 000 Hz The Aux Notch is very wide for easiest tuning and very deep Its 135 1 frequency range is by far the widest ever available for communications and should cover any signal 2 Function Select Switch PK NOTCH LP HP This switch and the Selectivity Frequency controls adjust the response of the main filter all but the Aux Notch PEAK bandpass passes a narrow band of frequencies and rejects others just the opposite of NOTCH LOWPASS passes low frequencies while rejecting high frequencies e g hiss HIGHPASS is the opposite of LOWPASS it passes high frequencies while rejecting low frequencies An exception occurs at high selectivity where LOWPASS and HIGHPASS take on some of the characteristics of PEAK 3 Selectivity Control In PEAK this control determines the filter bandwidth Peak bandwidth as narrow as 14 Hz 3 dB or 20 Hz 6 dB is available at 300 Hz The bandwidth gradually increases to 20 Hz at an 800 Hz center frequency and rea
9. espondence explaining that you are returning the unit Put everything INSIDE THE PACKAGE 4 Allow 1 3 weeks for any repair plus up to 2 weeks two way shipping in USA Please don t write about the status of the repair before this time Only 1 in 2000 packages are lost by shippers F IF WRITING 1 Most ask about things already covered in instructions Read again carefully They represent virtually everything we know about characteristics hookup problems etc There is little else to tell 2 Always state your purchase date 3 Always give full details Your rig phones or speaker exact hookup and detailed symptoms Most letters are much too vague We want to help you but have no idea of the condition of your rig your ability to follow the instructions or what you ve tried and no desire to carry on extensive correspondence Include all details in the first letter 4 We will not comment on any modifications to the QF 1A as inventive hams would make this a full time job 5 Enclose a self addressed stamped envelope for a much speedier reply O K to fold envelope 6 Not necessary to write before returning a unit Simply follow instructions E carefully G ALIGNMENT The circuit has two alignments Neither should require adjustment unless disturbed especially the Main filter Tracking alignment which is quite non critical The Aux Notch Depth alignment is more critical and sensitive Keep the i
10. etween the filter input plug and receiver jack 2 Especially if the receiver phone jack is on an auxiliary speaker try connecting some hookup wire between the speaker case and the receiver xcvr chassis or between the filter chassis 3 Try connecting a 10 to 47 ohm resistor across the receiver phone jack or other output to load it down PICKUP OF YOUR TRANSMITTED SIGNAL This should be extremely rare with the QF 1A as layout and RF bypass caps are excellent and show no sign of RF at 2 KW with the antenna 20 feet away and the cover off in our tests However some shacks especially using end fed antennas in the shack and or extreme RF on the 115 VAC AC line may possibly interfere with any audio gear Solutions in this case are 1 Plug the filter into an outlet away from the transmitter 2 Move the filter physically a few feet away from the strong RF source experiment 3 Try connecting pieces of hookup wire between various units in the shack to eliminate ground loops e g xcvr linear linear filter spkr case filter etc until all possible combinations have been tried 4 Use a good waterpipe ground to your rig 5 Try an L C RFI AC line filter available at a local Radio Shack or CB store 6 Read more in radio handbooks The above measures are rarely necessary as the QF 1A has been designed for use in high power transmitting stations So if you have a problem you must solve it in your shack and all shacks are different BAT
11. ey are not included despite their negligible cost NOTE 1 AUX NOTCH SETTING It s usually best to leave the Aux Notch at 11 000 until the main filter is adjusted for best results Set it at about 9 o clock for voice where it rejects a wide band of hiss and high frequency whistles Set it to reject any loud whistle or CW at other frequencies Table 2 CONDENSED VERSION OF Table 1 Condition Function Selectivity Main Frequency CW PEAK 8 o clock or more For best copy Voice Splatter LOWPASS As on panel 7 to 11 o clock Voice PEAK 7 to 9 o clock For best clarity Voice HIGHPASS 3 to 5 o clock 11 up 250 Hz 11 up Whistle Other QRM REJECT QRM Use Aux Notch to reject Use Aux Notch to reject whistle whistle Two Whistles NOTCH As on panel To reject whistle plus Aux Notch SSTV TTY HIGHPASS 10 to 12 o clock Same as Sel or use notches if whistles are problem E WARRANTY AND RETURNS We back our products better than most companies not just 90 days but one full year Our Attorney insists we supply the following lengthy description LIMITED ONE YEAR WARRANTY Autek Research warrants to the original consumer purchaser that its products shall be free of defects in workmanship and materials from one year from date of purchase WARRANTY LIMITATIONS This limited warranty does not cover and we are not responsible for any product which has been modified by the owner
12. ithout the narrow ultimate selectivity of the QF 1A Basically here is the truth ALL filters will produce audible ringing at bandwidths below 80 120 Hz and many poorly designed filters will ring even at wider bandwidths So the only way to eliminate ringing is to use wide bandwidth low selectivity on the QF 1A On the other hand a CW signal has a bandwidth less than 10 20 Hz so a very narrow filter can pass the entire CW signal and greatly reduce interference but at the expense of ringing The QF 1A gives you your choice at considerable increase in manufacturing complexity High selectivity will be found to be invaluable in very heavy QRM or pileups allowing you to hear signals inaudible at wider bandwidths but high selectivity is not as useful in thermal noise Note that gain at the peak increases at high selectivity while blasting when the desired signal comes through the narrow slot LOWPASS Produces an effect similar to PEAK at high selectivity Ignore LOWPASS Sel panel markings for CW reception If you listen to CW at a low note more than 12 o clock freq rotation you may find that you prefer LOWPASS But LOWPASS is wider and gain varies more Voice Signal with Splatter LOWPASS Adjust selectivity as on panel rotate frequency for best compromise between rejection of splatter and rejection of desired signal Frequency rotation beyond 8 10 o clock rejects desired signal heavily making it sound bassy The idea i
13. nput signal low to avoid saturation A scope is recommended at the filter output for most accurate alignment although an AC voltmeter or even the ear can produce acceptable results The alignment frequency of 800 Hz produces best results over the entire filter range However if you desire best results at another frequency far removed from 800 Hz i e 2000 Hz it may be better to align the filter at the frequency of most interest 1 Aux Notch Depth Alignment Adjusted by the 10K trim pot near the left side of the circuit board behind the Aux Notch pot and slightly to the right Feed in a signal at approx 800 Hz not critical Your receiver s calibrator beat note or a signal generator may be used 800 Hz is an average frequency for CW reception and occurs at about 10 o clock rotation of the MAIN frequency Then adjust the trim pot for minimum signal Now touch up the Aux Notch freq and repeat the trim pot adjustment for minimum signal Continue adjusting until no further improvement is noted 2 Main Filter Tracking Alignment There are two complete filters in series in the main filter These filters are adjusted to track by this alignment The alignment trim pot is directly behind the main 250 2500 Hz frequency control on the right side of the board Feed a signal at approx 800 Hz not critical into the filter Select peak and rotate Selectivity full 20 Hz setting Set the Aux Notch at 11 000 Peak the signal
14. or any malfunction or failure resulting from improper use improper applied voltage improper service or repair by the owner or his agent or from abuse neglect accident lightning damage fire use contrary to instructions or other causes beyond the control of Autek Research This warranty is made to the original consumer purchaser only and is effective only upon presentation of documented evidence of provable date of purchase This warranty covers only Autek products used for purposes as advertised We are not responsible for incidental or consequential damages Some states do not allow exclusion or limitation of incidental or consequential damages so the above limitation or exclusion may not apply to you This warranty gives you specific legal rights and you may also have other rights which vary from state to state CHECKLIST WHEN RETURNING A UNIT 1 Enclose definite proof of purchase date as described above with ANY return unless you simply wish repair out of warranty In this case enclose a check or MO for a minimum of 17 00 as described above plus 15 outside North America 2 ANY RETURN not complying with the above instructions will waste time and is subject to an additional 3 charge for correspondence or return COD without any action taken FOLLOW THE ABOVE INSTRUCTIONS 3 Enclose a detailed description of the problem and above checks proof of purchase date etc INSIDE the package Do not send separate corr
15. s to find the best cutoff frequency to maximize copy If splatter completely covers the desired signal or if two signals are on the same frequency the situation is impossible and no known method of signal processing will work Voice Signal Moderate Interference PEAK This position at moderate selectivity of 7 9 o clock and frequency adjusted for best copy can sometimes clean up signals and give more presence HIGHPASS Full frequency rotation 250 Hz and 3 5 o clock selectivity along with AUX NOTCH at 9 o clock can give greater presence under some conditions To reject lows or hum set frequency as little as 11 o clock with selectivity rotated about 2 3 of frequency Table 1 Continued Multiple Whistles or CW Normally AUX NOTCH is used But the MAIN NOTCH is deeper to 70 dB and can be made narrower at high selectivity Use notch Sel shown on panel The notch is not as deep at high selectivity so use minimum Sel rotation consistent with least rejection of desired signal Note To help find the notch frequency momentarily switch to PEAK at high Sel peak the whistle then switch back to notch at moderate selectivity Touchup the main frequency slightly since PEAK and NOTCH may not track perfectly For two whistles or CW or teletype QRM use both main and Aux Notch Weak CW An AC voltmeter or scope across the filter output is a big help in peaking weak CW Strong
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