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Old 09-03-2019, 07:06 PM
Mandy Mandy is offline
Join Date: Jun 2019
Location: Ridgecrest
Posts: 7
Default KY 197 Mysterious Transmit Issues

Hey Guys,

Just recently purchased an RV-4 a couple months ago and have absolutely been loving it.

I've been having some electrical issues that I've not been able to pin down. The one causing me the most stress has been my KY-197. ATC often reports me broken/unreadable when I transmit, giving me a QSA code of 5x2 (strong carrier, weak modulation). They pretty much describe it as mostly static when I transmit. However, I've not been having these issues when I'm close to the transmitter, like at an airport or flying formation.

So far, I've tried different headsets, tried turning all electrical equipment off (except battery and radio), tried different headset sockets, playing with ICS squelch settings, turning off ICS and going directly to radio, and cleaning the BNC connector on the antenna. My ICS works great and I can hear myself fine when I transmit on the radio. Receive function is also working great.

My two working theories are:

1) My ELT antenna (which is ~ 30 in. away and not in great shape) is soaking up some radiated power from the VHF antenna.

2) There is some modulation setting on the KY 197 not set up properly.

Anyone have any ideas? This problem really doesn't make sense to me. It seems I'm still transmitting a strong signal at range, but the carrier wave is not modulated properly... I've opened up the avionics bay before, but quickly closed it back up for fear of doing more harm than good.

Other random issues, which I'm not quite sure are related:

1) EchoUAT randomly disconnects in flight, then immediately reconnects.

2) Some reports of an intermittent transponder. Just recently had the transponder certified.


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Old 09-03-2019, 09:59 PM
Canadian_JOY Canadian_JOY is offline
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 2,474

Mandy - on the EchoUAT, you are definitely not the only user reporting disconnects. I participate in another type forum (membership fee based so can't post a useful link to the discussion there) where this issue has plagued at least two users despite good efforts from uAvionics to resolve. One recent post indicated a user from another forum "fixed" his disconnects by powering down his SPOT tracker. Hmmm...

As for the weak modulation on a KY197, there are so many places to start looking that, without additional information, we might send you off in entirely the wrong direction. You can start by doing some of the easy stuff. Change headsets and see if that makes a difference. If you have both pilot and copilot PTT's, try transmitting from the copilot side (doesn't mean you have to sit on that side, just use the copilot headphone jacks and PTT switch). Also, try to get a handle on when and where these poor readability reports are generated. Note also the direction of travel of the aircraft relative to the station reporting poor performance. This could be something as simple as signal blocking from a wingtip antenna. Also, there are lots of 197s around - see if you can borrow one from a neighbor or swap radios to see if the problem travels with the radio.

Report back on the above tests, plus provide a more complete description of your aircraft's avionics configuration and we might be able to get you a little closer to finding the cause.
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Old 09-04-2019, 01:47 PM
Mandy Mandy is offline
Join Date: Jun 2019
Location: Ridgecrest
Posts: 7

Thanks for the info! Good to know about the the EchoUAT - it really doesn't affect functionality, but it's annoying to have ForeFlight display "EchoUAT Disconnected" about 4-5x each flight.

I've done most of the easy stuff so far. Changed headsets. Used both PTTs. Just did a quick Google search, but didn't have any luck finding maps of ATC transmitter locations. Anyone know where the stations are for different frequencies? Barring that, I think my next logical step is a test flight against a known receiver. There's a automated radio check at my local airport. I'll do a test flight this weekend to see if I can reproduce with any specific geometries.

In the meantime, I'll try to figure out how to get this old ACK ELT antenna off for some additional troubleshooting.

Thanks again!
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Old 09-05-2019, 02:08 PM
WingsOnWheels WingsOnWheels is offline
Join Date: Mar 2009
Location: Plano, TX
Posts: 2,244

On the comm, I had a problem with with my KY97. I could hear people in the pattern just fine at my uncontrolled home airport, but had a lot of trouble with the local class D tower and ATIS. The radio bench tested and passed. I ended up removing a 90 degree adapter at the antenna and also putting a new bnc terminal on the cable at the antenna. I don't know which one was the cause, but everything works perfect now. I would check your coax for issues and the connectors. If you can find another aircraft at your airport, swap your comm in and give it a try.
Colin P.
RV-6A #20603
Complete 5/10/19
I donate every year on my B-Day (in Dec), but donated early in Sep'19.
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Old 09-15-2019, 10:45 PM
Mandy Mandy is offline
Join Date: Jun 2019
Location: Ridgecrest
Posts: 7
Default Solution! Kind of?

Thanks for all the help! After testing on the ground and in the air, I determined that it definitely was not a directional issue. Bought a cheap SWR meter and a Multimeter and took the avionics panel off. The coax from the radio is connected via BNC to some kind of relay which is mounted to the instrument panel. Then a separate BNC connector takes the cable to the antenna. Hooked up the SWR meter and everything looked great. Ranged from 1.2 to 1.4 with 5 W of power.

Then I broke the multimeter out and started testing coax. Lo and behold, it appears the coax from the radio to the relay is shorted somewhere. Just bought some BNC connectors and crimping tools and will attempt to fix tomorrow.

Had another question though -

I know the short could be anywhere along the wire and not necessarily at the BNC connector I tested. The connection to the KY197 is a right angle one. Is there any weirdness to taking that one off and repairing a solder? Or should i go ahead and buy a new 90 deg connector? Going in game plan is to chop off the BNC connector I have easy access to and test the wire. If it turns out the wire is bad along it's length, then I'll splice. I'm just worried that I'll find out the 90 deg connector is bad and I honestly have no idea how to go about repairing it.

Thanks again for all the help!
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Old 09-16-2019, 02:27 PM
jrs14855 jrs14855 is offline
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,644
Default adapter

Removing the 90 degree adapter requires good access to the front of the radio tray. You may need to remove the tray from the panel. The 90 degree is held in place by a snap ring.
I do not have a relay on mine and it is not shown in the installation manual IIRC.
I would get rid of the relay and install a new coax except for the angle adapter. If you still have problems tackle the adapter last.
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Old 09-16-2019, 02:32 PM
rocketbob's Avatar
rocketbob rocketbob is offline
Join Date: Jun 2006
Location: 8I3
Posts: 3,767

SWR meter will not tell you if the modulation is correct. You can transmit carrier only and get good SWR. You have to have someone check out the radio with a service monitor on the bench to determine if the modulation is within spec.

Also what kind of antenna do you have?

Please don't PM me! Email only!

Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
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Old 09-16-2019, 05:03 PM
BobTurner BobTurner is offline
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,858
Default Relay?

What would a relay be doing there? Unless carefully designed ($$) it will appear as a bad impedance bump, screwing up the transmission line. If it?s switching the antenna between two radios, there should be a third coax line. I don?t think I?ve ever seen such an arrangement, except in one very badly designed attempt to bring an antenna to the panel so a hand held could use it. If that?s what you have, you really should get rid of it. BTW, you mentioned ?splicing?. Another bad idea, for impedance reasons. Just buy new coax. Or, put male BNCs on both pieces, connect to a ?barrel? (female to female BNC adaptor).

As rocket Bob mentioned, this would be a source of a weak signal - not a strong signal, weak modulation.
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Old 09-16-2019, 07:36 PM
Mandy Mandy is offline
Join Date: Jun 2019
Location: Ridgecrest
Posts: 7

Hey guys,

Thanks again for all of the input! Just to clarify - the SWR meter didn't tell me anything. Just another unnecessary toy to have laying around the hangar. I probably shouldn't have bought it, but maybe it'll come in handy someday.

The problem I found was when I was testing the coax cable from the radio to the relay with a Multimeter. I got a "short" when I applied the leads to the center wire and the outside of the BNC, which told me that coax is bad.

So I've been wondering what that relay is about and it turns out that there is a small 3.5mm headphone jack plug in on the instrument panel. I guess the builder had it there for a handheld radio. It's actually pretty fortuitous that it was there because I have much less coax to replace.

Copy on the barrel connectors. Just ordered a couple of them. Current plan is to cut the coax and find the short, install a new BNC connector, and then use a barrel connector to put it directly to the antenna, bypassing the handheld relay.

Thanks again!

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Old 09-16-2019, 11:01 PM
BobTurner BobTurner is offline
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,858

You do need to be careful with ohmmeters around RF stuff. Some perfectly good antennas will show zero dc resistance to ground, or an open circuit to the antenna radiating element.
By all means, get rid of that handheld ?adaptor?. It uses a phone plug instead of a real coax connector; and what you?re calling a relay is a mechanical contact activated by inserting the phone plug. No impedance matching of any sort. It belongs in the trash.
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