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Thread: TSO Com?

  1. #121

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    Quote Originally Posted by bob turner View Post
    Did I mention that the GTR-200B is TSO if used in conjunction with a G-750 or something? Only difference - 200B has Bluetooth.
    Where is that documented? The installation manual that I have on file shows:

    "1.4 Certification

    The GTR 200/200B does not have TSO authorization.
    The GTR 200B Part Number 011-02980-40 has FAA-PMA"

  2. #122
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    Quote Originally Posted by bob turner View Post
    Dave - I agree that this is a minor alteration - but perhaps the 337 is a tool to approve an otherwise unapproved part? I am going to try it both ways.
    It CANNOT be a major (requiring a 337) as per part 43, appendix A, (a). You are NOT altering ANY structure or the design of any system such as the electrical system. This means that the installation of that radio is a minor alteration and as such needs to be documented by an entry in the airframe log as per 43.9, (a). Part 43.9, (d) requires ONLY major repairs/alterations to be documented on a 337.

    Web
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  3. #123

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    Quote Originally Posted by wireweinie View Post
    It CANNOT be a major (requiring a 337) as per part 43, appendix A, (a). You are NOT altering ANY structure or the design of any system such as the electrical system. This means that the installation of that radio is a minor alteration and as such needs to be documented by an entry in the airframe log as per 43.9, (a). Part 43.9, (d) requires ONLY major repairs/alterations to be documented on a 337.

    Web
    Part 43 Appendix A is only part of the considerations for Major/Minor determination. You need the definition in Part 1 - Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications—(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
    (2) That is not done according to accepted practices or cannot be done by elementary operations.

    I agree that a radio installation does not meet the definition, however since Bob asked about the radio interference issue, the FAA might say it fits the "other qualities affecting airworthiness". I find that a stretch as airworthiness has nothing to do with the ability to communicate by radio.

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  4. #124

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    Quote Originally Posted by bob turner View Post
    Did I mention that the GTR-200B is TSO if used in conjunction with a G-750 or something? Only difference - 200B has Bluetooth.

    Dave - I agree that this is a minor alteration - but perhaps the 337 is a tool to approve an otherwise unapproved part? I am going to try it both ways. I thought I had high level backing for all this - now not so sure.
    Bob, this falls right in there with API tailwheels. CAR 4 and CAR 3 have no requirements for a tailwheel to be "approved". I know of a lot of them that have been installed as minor alterations, and they don't have any approval (TSO or PMA). As long as you meet the appropriate certification basis, it is OK. Think fuel gages, Champs, Vagabonds, and Clippers all use Model A fuel gages. My Howard had Ford window regulators to run the windows up and down, and a lot of other automotive parts. There was no PMA system when these airplanes were built. The current TSO system is an outgrowth of the CAR 15 Type Certificates. Go look at some old floats or wheels and you will find Type Certificate numbers instead of TSO numbers!

    This guy is just yanking you around. Unfortunately you opened a can of worms when you asked about the frequency interference. The only thing that they could get you on is CAR 4.500 that says each piece of equipment installed needs to function properly (paraphrase). Since you are getting bleed through, they can say it isn't functioning properly.

  5. #125

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    Quote Originally Posted by dgapilot View Post
    The only thing that they could get you on is CAR 4.500 that says each piece of equipment installed needs to function properly (paraphrase). Since you are getting bleed through, they can say it isn't functioning properly.
    I submit that the cause of the interference is not yet proven. If the interfering signal is a first order intermodulation product, and if the GTR 200 meets RTCA DO-168B requirements for skirt band width (adjacent channel rejection), then the blame for the problem falls squarely on those who allocated the ATC frequencies.
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  6. #126

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    Quote Originally Posted by frequent_flyer View Post
    I submit that the cause of the interference is not yet proven. If the interfering signal is a first order intermodulation product, and if the GTR 200 meets RTCA DO-168B requirements for skirt band width (adjacent channel rejection), then the blame for the problem falls squarely on those who allocated the ATC frequencies.
    After a bit of research I found what appears to be the governing document for FAA frequency planning:

    ORDER 6050.32B SPECTRUM MANAGEMENT REGULATIONS AND PROCEDURES MANUAL

    A search for "intermodulation" finds several references that show the authors understood the potential problem. Specifically CHAPTER 9. VHF/UHF AIR/GROUND COMMUNICATIONS FREQUENCY ENGINEERING includes this text:

    "c. Cosite analysis is necessary to prevent RFI resulting from the interaction of transmitter and receivers at or near the same site, which may be far removed in frequency. These sources can be FAA equipment in the same building, or high power or broad-spectrum emissions such as AM/FM/TV broadcast stations from a few miles away. Cosite RFI includes intermodulation, spurious emission, cross-modulation, harmonic, image, and overload interference. A discussion of cosite interference is found in Appendix 2."

    If this problem were impacting me I'd be asking to see the co-site analysis that resulted in allocation of frequencies 132.2 and 257.875. A first order intermodulation product is 125.675 which is 25 kHz away from a proximate tower frequency of 125.7. The potential for interference seems to have been ignored if any analysis was performed.
    Last edited by frequent_flyer; 07-21-2021 at 06:29 PM.
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  7. #127

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    I am delighted with that post. If I get this sorted out, I will ask them about that. As it is, it seems that asking stuff like this just pisses them off.

    I guess I had a momentary brain glitch. The AC clearly states that a field approval request must be turned down for a minor alteration. I think I am on excellent legal footing, but I do not have the power to overrule a zealous ASI.

  8. #128

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    Temperatures in Arizona are well below normal today so took the IFR NAV 750 test set to the hangar to try to measure my GTR 200 skirt bandwidth (adjacent channel rejection). My measurements seem to show that my GTR 200 has more than 20 dB better rejection at 25 kHz offset than required by DO-168B.

    I loosely coupled the NAV 750 generator to the COM antenna and ran two tests. Test 1 measured the signal level required to break squelch. Test 2 was run with squelch overridden and the signal level was increased until the generator modulation tone was just audible above receiver noise. Three conditions were used for each test.

    Condition 1 - GTR 200 tuned to 125.700, generator radiating at 125.700
    Condition 2 - GTR 200 tuned to 125.700, generator radiating at 125.675
    Condition 3 - GTR 200 tuned to 125.700, generator radiating at 125.725

    Test results shown below:
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  9. #129

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    That seems to say the radio has a narrow bandwidth. The possibility of broadening the difference signal, coupled with an inadequate squelch range, may be my problem. Thanks for doing that.

    I just put 22 hours in, flying the Cub to northern Calif and back. Absolutely no noise or interference anywhere, other than that noise when we are on 125.7 three miles away from the offending transmitters. I talked to towers, approach controls, unicoms - lots of folks. These are good radios - it is just a very local problem.

  10. #130

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    Quote Originally Posted by bob turner View Post
    The possibility of broadening the difference signal, coupled with an inadequate squelch range, may be my problem.
    A couple of questions. Have you confirmed that a difference signal is detectable when tuned to 125.675? What do you mean by "inadequate squelch range"?

  11. #131
    wireweinie's Avatar
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    Hey Bob

    When you install a better radio, let me know. I'll make a wire harness free of charge. Just to end the pain.

    Web
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  12. #132
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    Web,
    Bob has been reporting these issues for a long time. Why does he have no interference when away from his local airport, then when he returns home the interference begins again? I recall he has mentioned some sort of issues in combination with a local auto dealership's radios. Is it not likely it is the auto dealership's radios which are creating the problem and not Bob's radios?
    N1PA

  13. #133

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    Bob, without going through the entire thread, Iím curious, is this happening with multiple radios of the same make/model, or only one? Have you tried swapping different radios in the offending airplane to eliminate an installation problem?


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  14. #134
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    Quote Originally Posted by skywagon8a View Post
    Web,
    Bob has been reporting these issues for a long time. Why does he have no interference when away from his local airport, then when he returns home the interference begins again? I recall he has mentioned some sort of issues in combination with a local auto dealership's radios. Is it not likely it is the auto dealership's radios which are creating the problem and not Bob's radios?
    He operates in an area with a lot of electrical 'noise', meaning other entities that transmit RF signals. Any radio that has inadequate design feature to protect it from outside interference will be susceptible to making noise on your headset. If you operate another model of radio such as a KY97A you will have less/no interference due to the design of the radio.

    Interference is more easily produced on a frequency multiple such as 2X or 3X the frequency OR 1/2 or 1/4 frequency etc. But keep in mind that a very strong signal will overpower a radio whether it's frequency is on a multiple or not. Think about testing a com inside a hanger. If you set the com to something like 123.45 mhz and hit the PTT button it will blank out an FM radio set to 100.5 mhz (100.5 The Fox!).

    So, yes the dealership radios are creating the interfering signal, but the radio could have been designed more robustly to prevent those problems. Lots of examples of design short comings like this. Compare an Icom to a Bendix/King radio or a Flightcom compared to a Trig or Becker. The cheaper radio works adequately but will never work as well as the better designed radio will. So if you operate in an area like Bob, with lots of known 'noise', pick the best radio you can.

    Web
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  15. #135

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    Web is correct, of course. The radio itself has an inadequate squelch range. It would have cost nothing for Garmin to use the SL-40 squelch circuitry.

    Of course I did not know that when I bought the first one. I personally factor in cost when buying anything, which is probably why I drive a 1965 Mustang instead of a 2015 Maserati. Or a J3 instead of a Carbon Cub.

    But the display, memory frequency selection, and stunning intercom are so far superior to anything I have ever used - and except for that one frequency, communications are superb as well - that, unless you spend time in MYF north pattern, this radio is simply perfect!

  16. #136

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    I have read the entire thread but I found no mention of any adjustment of the squelch threshold. Was that attempted or is this GTR 200 still set at factory default? Ref installation manual 3.6.4.2 COM Setup Page:


    "RF SQLCH
    Increasing this setting increases the signal level required to break squelch. Receiver
    squelch can be set from 0-10, a setting of 0 (default) represents the factory
    calibration."
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  17. #137
    Dave Barras's Avatar
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    Squelch threshold is one thing, engineering circuits to reject harmonic interference is something else.
    Dave


    YOU NEVER KNOW
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  18. #138

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    Set at 10. All of them.

    Do we call the difference frequency a "harmonic?"

  19. #139

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    Quote Originally Posted by bob turner View Post
    Do we call the difference frequency a "harmonic?"
    No.

    A "harmonic" is a signal that is an integer multiple of the fundamental frequency. Harmonics can produce intermodulation products but, by definition, not first order intermodulation products. You have provided evidence of interference by a first order intermodulation product.

    "All of them"? I see only one RF squelch threshold setting.
    Last edited by frequent_flyer; 07-26-2021 at 06:32 AM.
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  20. #140
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    Quote Originally Posted by dgapilot View Post
    Bob, without going through the entire thread, I’m curious, is this happening with multiple radios of the same make/model, or only one? Have you tried swapping different radios in the offending airplane to eliminate an installation problem? ......
    I'm curious too.
    That way you'd either zero in on or eliminate the possibility of one particular unit being the problem.
    Cessna Skywagon-- accept no substitute!

  21. #141

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    Ten radios, including one GTR-200B. Two installed by FAA repair stations. All with RF Squelch set at 10 (max). Only on 125.7, and only when both controllers key their mics simultaneously. We do not get interference from airborne transmitters. We have identified the frequencies mathematically and by the clearances given. During Covid, only one controlller ran both transmitters. Then we would get each and every transmission in its entirety.

    So far, only one of the feds even understands what heterodyne means - and his job is to give me a run for my money on the non-TSO bit. Nice guy, and knowledgable - bet he wouldn't be doing this without somebody else shoving.

    By the way, the "B" seems worse. Garmin produced the "B" after I started trying to get them to redesign the squelch circuit. I am betting this only happens in this one isolated spot, and that the FAA could fix it if they wanted to.

  22. #142

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    Quote Originally Posted by bob turner View Post
    FAA could fix it if they wanted to.
    Bob

    You have presented evidence that shows your interference is caused by a first order intermodulation product of two FAA control frequencies. It is possible that the intermodulation product is produced at the transmitter site, in the GTR 200 itself, or even by some mixing mechanism not associated with either.

    If I lived in the San Diego area I'd take a spectrum analyzer to the transmitter site to confirm that it is the source of the interfering frequency. A less rigorous test is to listen to the frequency with an aircraft band radio. I have asked several times for you to confirm that you hear the interfering signal when the GTR 200 is tuned to 125.675 but. so far, have seen no confirmation of that.

  23. #143

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    Quote Originally Posted by bob turner View Post
    So far, only one of the feds even understands what heterodyne means
    They don't need to understand heterodyning or mixing products. They don't need to know what COM radio exhibited any problem. If, and when, you have proof that the transmitting site is radiating a strong signal at 125.675 then you go to FAA, and/or FCC, and lodge a complaint.
    Last edited by frequent_flyer; 07-26-2021 at 11:37 AM.
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  24. #144

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    Yeah, and then they find some reason to haul you through the coals. Never again - I shall let others point out problem areas to the feds.

    I wasted some time last year pointing out that we had paved a runway to 150' width, then striped it down to 75'. Answers were -um - puerile.
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  25. #145

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    Last week I had to acknowledge the pilots bill of rights. This week I was informed that a non-TSO radio voids the airworthiness certificate, and that I could be violated for each flight subsequent to installation.

    This means you will have to send my mail to Guantanamo - the first was installed in 2016, and these aircraft fly darn near every day.

    The guy who delivered this news is new, and is being guided by someone else. He is a very pleasant guy, and I do not mind working with him. He was just delivering a message. He also says he has found a "job aid" that places any avionics installation in the major alteration category. He promises a link. More on that later.

    And -surprise! Giving a flight review in a Super Cub today, and just incidentally explained the interference problem. The student (owner) said "is that what all that noise comes from!"
    The radio? A Garmin GNC 300 XL TSO. The plot thickens.

  26. #146
    wireweinie's Avatar
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    He also says he has found a "job aid" that places any avionics installation in the major alteration category. He promises a link. More on that later.
    Now THAT I'd like to see.

    Ask around for info on the head of legal for your FSDO. This may end up in his office.

    Web
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  27. #147

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    Quote Originally Posted by wireweinie View Post
    Now THAT I'd like to see.
    Perhaps this document - major_repair_alteration_job-aid.pdf

    I'm not trusted to provide the URL but it should be top of the results in a Google search. A search for "avionics" finds multiple results.

  28. #148

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    TSO Com?

    Quote Originally Posted by bob turner View Post
    Last week I had to acknowledge the pilots bill of rights. This week I was informed that a non-TSO radio voids the airworthiness certificate, and that I could be violated for each flight subsequent to installation.

    This means you will have to send my mail to Guantanamo - the first was installed in 2016, and these aircraft fly darn near every day.

    The guy who delivered this news is new, and is being guided by someone else. He is a very pleasant guy, and I do not mind working with him. He was just delivering a message. He also says he has found a "job aid" that places any avionics installation in the major alteration category. He promises a link. More on that later.

    And -surprise! Giving a flight review in a Super Cub today, and just incidentally explained the interference problem. The student (owner) said "is that what all that noise comes from!"
    The radio? A Garmin GNC 300 XL TSO. The plot thickens.
    Since he seems to be bullying you, simply ask him for the letter of investigation that must be provided to anyone under investigation for infractions of 14 CFR. The LOI has to articulate the exact regulations you are suspected of violating.

    Iím sure he is referring to the AFS-300 major repair and alteration job aid. Section d13a, which only talks about avionics that perform critical functions. Communications is not a critical function! There is nothing in CAR4 (the J3) or CAR 3 (the PA-1 that says you need a TSO radio (TSO didnít even exist until the FAA, back then it was items certified under CAR 15).

    For now, he is just yanking your chain, once a LOI is issued, then FAA legal gets involved, and this guy has a whole lot more paperwork to do, and he has to justify his position based on the regulations. Based on the definition of major alteration in 1.1, the definition of major change in type design in 21.93, the list of major alterations in 43 Appendix A, the guidance in AC 43-210A, and the guidance in the AFS-300 job aid, I donít think he has a leg to stand on. Combine that with FAA telling IAs and mechanics that radio installations are minor alterations for the last 20 years, I donít see a case that this guy could make.


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    Last edited by dgapilot; 07-28-2021 at 08:51 AM.
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  29. #149

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    Oh, hot digs! I just found AC 20-67B. I will post it when I get to the big computer. It is a single page, and paragraph 5 says "An acceptable means of compliance . . . is to satisfy . . .RTCA . . . DO-186 . . ."
    The GTR-200 complies, according to Garmin.

    I have carefully gone through the major/minor job aid - it screams "minor." We shall see . . .
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  30. #150

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    Well hopefully that will remove the monkey as AC 20-67B makes DO-186 an acceptable means of compliance even for IFR!
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  31. #151

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    I love seeing people use FAA publications to support their positions. That AC even goes so far as to say it is acceptable for IFR!


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  32. #152

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    Yeah, and for Part 23 airplanes!
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    So it has been over a month since I have heard from the FAA. You may recall they read me my rights, told me I could be violated for each and every flight, and contacted me roughly twice a week for a month.

    I asked for a written explanation as to why this was a major alteration, and shared the above feelings about "must meet TSO" along with their very own definition of "meets" - and have heard nothing since.

    We did get a report of interference in a TSO Garmin 300, so it isn't the lack of a TSO that is causing the extra noise. But now I am afraid to poke them - they may want to start scrutinizing other things. And I admit - a serious sleuth could find things I have done wrong - if he looked hard enough. I think I blew through a frozen red light last week, after carefully checking for cars with racks on top.
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  34. #154
    Gordon Misch's Avatar
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    Atta Boy, Bob. "show me the reg".
    Gordon

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  35. #155

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    Quote Originally Posted by bob turner View Post
    So it has been over a month since I have heard from the FAA. You may recall they read me my rights, told me I could be violated for each and every flight, and contacted me roughly twice a week for a month..
    Yes, a lot of time has gone by and you still have not answered - " I have asked several times for you to confirm that you hear the interfering signal when the GTR 200 is tuned to 125.675 but. so far, have seen no confirmation of that."

    If the mixing is not at the TX site the signal will not be heard on 125.675 and perhaps may be fixable with a simple 1/4 wave stub at your antenna connector.
    Last edited by frequent_flyer; 09-02-2021 at 07:20 PM.
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  36. #156

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    Yeah - sorry. I will do that tomorrow.

  37. #157
    wireweinie's Avatar
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    Umm . . . .

    Web
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    His point is well taken, although I think I would have phrased it differently. I get to the airport and am usually so full of joy that I forget little easy tasks like this.

    Today I took the J4 up - it has the newest and noisiest 200 - and with the cooperation of the tower folk, spent 15 minutes on 125.675. Nada. Not a peep. Silent.

    While that may not be definitive (I could have picked the exact 15 minutes where no simultaneous transmissions occurred), I note that twice on the climbout (125.7) and once on the descent I had approach control interference.

    Only thing I can figure is that there is some non-linear anomaly somewhere. Not sure what you mean about a quarter wave stub, since my antennae are all 1/4 wave. But willing to try . . .

  39. #159
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    Quote Originally Posted by bob turner View Post
    ..... Not sure what you mean about a quarter wave stub, since my antennae are all 1/4 wave. But willing to try . . .
    Basically this> http://www.arcticpeak.com/antennapag...erwavestub.htm It's potentially a notch filter for a frequency of interest, but with some qualifiers as noted. The VF of the stub is important to get the right tuning.

    Gary

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    Quote Originally Posted by bob turner View Post
    His point is well taken, although I think I would have phrased it differently. I get to the airport and am usually so full of joy that I forget little easy tasks like this.

    Today I took the J4 up - it has the newest and noisiest 200 - and with the cooperation of the tower folk, spent 15 minutes on 125.675. Nada. Not a peep. Silent.

    While that may not be definitive (I could have picked the exact 15 minutes where no simultaneous transmissions occurred), I note that twice on the climbout (125.7) and once on the descent I had approach control interference.

    Only thing I can figure is that there is some non-linear anomaly somewhere. Not sure what you mean about a quarter wave stub, since my antennae are all 1/4 wave. But willing to try . . .
    The phrasing of my post was inappropriate and I have edited it.

    Gary's later post shows he understands what I have in mind. If the mixing product is not heard on 125.675 then there is a good chance it is generated in the receiver itself. A possible way to prevent that is to notch out the 257.875 MHz signal before it gets to the radio. If you tell me what connector is used at the base of your antenna (probably BNC or TNC) I can try making a stub and tuning it (I have the tools to do that). You would put this stub between the antenna and the antenna coax with a T fitting and see if the problem is fixed.

    So - let me know the antenna connector type, confirm 257.875 MHz is the UHF ATC frequency, and I'll see what I can come up with. No guarantee it will work but it's worth a try.

    Here is a reference for those unfamiliar with using stubs as filters -
    http://www.arcticpeak.com/antennapages/quaterwavestub.htm (there are many others).

    Edited to add - a photo of the antenna base and coax would also be useful so I know what space I have to work with.

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