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KY97A Problems

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rv6ejguy

Well Known Member
I've been flying with no radio problems for 10 years but now after the big overhaul, both my KY97As are horrible when transmitting- not always but often. They are crystal clear receiving but have very high levels of noise when transmitting, when comm 1 is bad, I can hear the noise in the headphones, when clear, comm 1 also sounds clear.

Comm 2 sounds clear in the headphones when transmitting but is unreadable by the tower 100% of the time.

I did a lot of work behind the panel but all down low, away from the radios and wiring which are up high.

I checked and moved grounds to separate locations yesterday, no real improvement.

Any ideas from the VHF gurus here on where to look? I am out of ideas now and ready to rip out all the wiring and start over.:(
 
Start with the antenna connections. Make sure the antennas are properly bonded (grounded) to the aircraft skin.
 
If you don't have a good ground on the engine it turns your airplane into a large capacitor. Capacitance cancels inductive reactance so that can have an effect on transmit performance.
 
PCHunt said:
Start with the antenna connections. Make sure the antennas are properly bonded (grounded) to the aircraft skin.
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Hmmm, they have never been specifically grounded to the skin and worked perfectly for 10 years that way. Each radio has its own SS whip antenna mounted with the supplied ceramic isolators. Transmission signal is strong, just a lot of noise on it and comm 1 works perfectly about 1/3 of the time.

I will check this out but it does not seem like this would cause an intermittent noise problem, just a weak transmission.
 
rocketbob said:
If you don't have a good ground on the engine it turns your airplane into a large capacitor. Capacitance cancels inductive reactance so that can have an effect on transmit performance.
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I have triple separate grounds between the engine and airframe due to my electrically dependent nature but I will ohm check all three anyway. Thanks.
 
Try taking some scotchbrite to the mic and phone plugs and jacks and clean them up. Most scratchy noise problems originate in this area.
 
rv6ejguy said:
...

I checked and moved grounds to separate locations yesterday, no real improvement.

Any ideas from the VHF gurus here on where to look? I am out of ideas now and ready to rip out all the wiring and start over.:(
Click to expand...

If your mic jacks are not properly isolated from chasis ground at the mounting surface, your "audio common" will be useless. You could have a "ground loop" path between your mic jacks. You may need to try wiggling the mic jacks with your finger for very intermittant problems.

With both radios removed from their trays, isolate your audio common (disconnect audio common wires from the grounding stud). Then test for a short between the barrels of your mic jacks.

I've had this happen in retro-fitted intercom systems where the barrels make intermittent contact with the airframe at the mounting surface. Sounds like intermittent static with very little modulation to any recievers, yet may not sound that bad to you via side-tone.
 
Last edited:
N804RV said:
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With both radios removed from their trays, isolate your audio common (disconnect audio common wires from the grounding stud). Then test for a short between the barrels of your mic jacks.
Click to expand...

This should say, "then test for short between each of the barrels of your mic jacks and ground."

I musta been pretty sleepy when I wrote this.
 
rv6ejguy said:
I have triple separate grounds between the engine and airframe due to my electrically dependent nature but I will ohm check all three anyway. Thanks.
Click to expand...

Go to one ground (temporarily) and see if things improve. Ohm checks wont tell you much since impedance can change with frequency. Thats why strap grounds work better than regular cables, they have low impedance at RF frequencies.

Once on here there was a gent that was having issues with transmit performance and it turned out to be his belly skins not screwed to the wing skins. Even though the spar guarantees DC continuity, RF is a different animal.

Also if you have any additional ductwork you might want to check to see thats grounded well.
 
rocketbob said:
Go to one ground (temporarily) and see if things improve. Ohm checks wont tell you much since impedance can change with frequency. Thats why strap grounds work better than regular cables, they have low impedance at RF frequencies.

Once on here there was a gent that was having issues with transmit performance and it turned out to be his belly skins not screwed to the wing skins. Even though the spar guarantees DC continuity, RF is a different animal.

Also if you have any additional ductwork you might want to check to see thats grounded well.
Click to expand...

Good points. I build electronics all day long 5 days a week but know nothing about RF stuff. Appreciate the tips everyone. Thanks. Wanna find this and fix it so I can continue the test program. I am grounded until I do.
 
KY97A TSO problems

Hello, I am from Belgium and have a KY97A TSO on my aircraft. It has been working perfectly for 10 years but now when I start it it will refuse to transmit or receive for about 15 minutes. The panel will show a blinking TX. After 15 minutes I will be able to start hearing the controller and be able to answer but his answer will not be hearable...what could be the problem? People tell me I should be looking for antenna connections? Can you help for troubleshooting? Thank you in advance. Best regards

JL
 
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