KX155 radio noise on 1 freq

[LucasC]

Soooo. Since I bought the C a few years ago Ive had some intermittent radio noise on only 1 frequency(123.00)  All other frequencies are crystal clear. As soon as another pilot talks on 123 it clears up but as soon as there done, noise is back. Noise is steady now when nobody is talking. not intermittent anymore. Drives me crazy. Any ideas?

Lucas

[MikeOH]

Is it sensitive to squelch?

Is it present with the engine shut down?

Is it present with all other avionics off?

[carusoam]

The 155 is a pretty common radio...

Sounds like you have a noise that this radio is hearing... On one frequency...

123.00 is probably the most used intercom..? Expect lots of noise...

What do you have for comm2 is it always tuned to the same frequency?

Some radios blast lots of noise if com2 is a Narco... make sure it is turned off while testing...

Swap in a borrowed KX155 to see if anything changes...

See what Alan has on the magic radio shelf if you find out what is making the noise...
 

Best regards,

-a-

[N201MKTurbo]

My kx155 does it on 119.4. It is interference coming from my $20000 Avidyne. Avidyne says they can't reproduce it, but I've seen the same interference on 4 different Avidynes, everyone I've looked at. Most don't cause any issues, but you can see it on a spectrum analyzer.

Anyway, I digress. I would turn off everything else in the plane and see if it is coming from some other piece of equipment.

[PTK]

4 hours ago, LucasC said:

Any ideas?

What voltage regulator do you have? Does it happen with the engine off on the ground? If not, it may be from the voltage regulator. If It happens with the engine off pull the circuit breakers one at a time to see if it goes away. If it persists its probably from the radio itself. Does it go away with squelch disabled? If not the squwlch may need to be adjusted. 

[carusoam]

Wicked old radios are noisy..

Really old radios are sensitive to noise...

20k radios have some good filtering skills to avoid noise...

One might consider adding a new filter in line with the sensitive radio...

One might also considering swapping out the ancient radio....

PP thoughts only, not a radio guy...

Best regards,

-a-

[LucasC]

It happens when engine off too but seems to be more intermittent. Weird that its only on 1 freq? If a filter is added how does that work? I will try pulling breakers. I only have 1 nav/com and I've tried shutting of all lights, transponder etc. and has brand new generator and electronic voltage regulator. 

[LucasC]

1 hour ago, PTK said:

What voltage regulator do you have? Does it happen with the engine off on the ground? If not, it may be from the voltage regulator. If It happens with the engine off pull the circuit breakers one at a time to see if it goes away. If it persists its probably from the radio itself. Does it go away with squelch disabled? If not the squwlch may need to be adjusted. 

How do you disable squelch? 

[carusoam]

Power wires for radios can act like antennas...

Something may be causing noise in the power wires.... that noise shows up in your radio as sound....

A filter is a big capacitor... that makes little waves disappear....

Many Mooneys have a filter for their radio wires...

PP explanation of what electrical engineers and technicians know... I’m not an EE or tech...
 

 

Best regards,

-a-

[PTK]

7 hours ago, LucasC said:

How do you disable squelch? 

I should’ve said with “automatic” squelch disabled. When the volume knob is pushed in it activates automatic squelch. With knob pulled out it overrides the automatic squelch and you can test and adjust volume.

[takair]

Do you have portable GPS or USB charger?  Start with those.  Many of the USB chargers are known to cause intermittent noise.

[LucasC]

1 hour ago, PTK said:

I should’ve said with “automatic” squelch disabled. When the volume knob is pushed in it activates automatic squelch. With knob pulled out it overrides the automatic squelch and you can test and adjust volume.

Yes i tried that and no change

[LucasC]

Sending to my radio guy to check it out and at the very least do a tune up.  See what happens when i get it back. 

[PTK]

5 hours ago, LucasC said:

Yes i tried that and no change

It sounds like you have a squelch issue. There are  capacitors in there that have a life limit which varies depending on how the airplane has been stored inside or outside. It has to be analyzed down to the component level by someone who knows what they are doing.

I think what I would do first is verify that it is the radio and not something else. Swap it out if you can find someone to lend you one. This will tell you if the issue goes with the radio or stays behind. Once that's confirmed you can send it out. 

You may want to give these guys a call...

http://www.kx-155.com/

[LucasC]

I agree PTK

[MikeOH]

10 hours ago, PTK said:

It sounds like you have a squelch issue. There are  capacitors in there that have a life limit which varies depending on how the airplane has been stored inside or outside. It has to be analyzed down to the component level by someone who knows what they are doing.

I think what I would do first is verify that it is the radio and not something else. Swap it out if you can find someone to lend you one. This will tell you if the issue goes with the radio or stays behind. Once that's confirmed you can send it out. 

You may want to give these guys a call...

http://www.kx-155.com/

I'm curious as to your reasoning why a squelch issue would depend upon the receiver frequency.

[M20F]

Had this issue for years on my Mooney.  Mentioned to a guy on a 5hr flight.  About 2hrs in he pulled the storm scope breaker, problem solved (probably a more permanent solution to be had but I am cheap).  
 
My suggestion would be pull breakers till you find it as my situation was exactly as described. 

[LucasC]

Got the radio back from mikes avionics out of AZ. He couldn't pin point a problem necessarily but he realigned the radio to specs and all is well now. I recommend for older king and narco problems. Clear as a bell now.  

[carusoam]

Great follow up Lucas!

Best regards,

-a-

[chriscalandro]

On 7/16/2020 at 10:34 PM, MikeOH said:

I'm curious as to your reasoning why a squelch issue would depend upon the receiver frequency.

It could be picking up some light interference at or around that frequency, enough to open it up. 
 

but it’s probably the fuel caps. 

[MBDiagMan]

Something is Generation on that frequency or a harmonic.  Calculate the harmonics and try to see if there is something on that frequency interfering.  Multiply 123.0 x2, x3 & x4.  Divide 123.0 by 2, 3 & 4.  Try to figure out if there is anything that could be generating even a low level signal at those frequencies.  Maybe a strobe circuit, bad example, but try to find anything at all.  You have the best test instrument, the radio itself.  Disconnect everything els in the plane that you can.  If you lose the noise then start hooking up things one by one.

if you can borrow the same radio and slide it int to eliminate the radio itself before all this trouble that would be great, but I really expect that it is a harmonic or identical freq noise source.

[MikeOH]

1 hour ago, MBDiagMan said:

Something is Generation on that frequency or a harmonic.  Calculate the harmonics and try to see if there is something on that frequency interfering.  Multiply 123.0 x2, x3 & x4.  Divide 123.0 by 2, 3 & 4.  Try to figure out if there is anything that could be generating even a low level signal at those frequencies.  Maybe a strobe circuit, bad example, but try to find anything at all.  You have the best test instrument, the radio itself.  Disconnect everything els in the plane that you can.  If you lose the noise then start hooking up things one by one.

if you can borrow the same radio and slide it int to eliminate the radio itself before all this trouble that would be great, but I really expect that it is a harmonic or identical freq noise source.

I believe the OP's problem was solved by having the radio repaired/realigned. 3 posts up from yours.

[MBDiagMan]

Whoops!

[Jim Peace]

I had a similar issue the other day...I was using a newer GTR225...first time in over 2 years I have experienced it...I was on a freq (JAX center) I never use.....all other freqs okay....This one drove the sidetone nuts when I transmitted....makes me think I am unreadable....did not bother trying my GTN650...just did not care enough....electrons are crazy.....and don't get me started on photons......

[FlyingDude]

@Andy95W similar issue to yours.

Also read:

https://rec.aviation.owning.narkive.com/YVebnSHJ/kx155a-kx165a-with-lower-gps-interference-in-the-rf-output

Some ideas were: higher grade coax cables, better grounding of coax cable at terminals, ferrite beads at cable ends, better routing of power leads to kx155, prayer, blood sacrifice.