Intercom Tone When Transmitting
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
Intercom Tone When Transmitting
Well, it has been a long winter of rewiring behind the panel of my 170A. I replaced fuses with circuit breakers and added a switch on an empty piano key for new LED anti-collision lights. I didn’t make any changes to my intercom or radio other than crimping on new terminals to the power and ground wires and I re-routed the wires for my pilot headset jacks. No circuit changes. Oh, I did replace the coax for my radio antenna.
However... now I am getting an annoying and loud tone in the headset when I hit the push to talk button. I didn’t have any other headsets plugged in at the time. I switched the intercom to isolate and still get the tone when transmitting. Any thoughts on what I should look for? Is this indicative of a ground loop?
For reference I have a KX170B nav/com and an Intervox four place intercom.
Looking for troubleshooting advice. Thanks in advance. You guys are great.
Doug
However... now I am getting an annoying and loud tone in the headset when I hit the push to talk button. I didn’t have any other headsets plugged in at the time. I switched the intercom to isolate and still get the tone when transmitting. Any thoughts on what I should look for? Is this indicative of a ground loop?
For reference I have a KX170B nav/com and an Intervox four place intercom.
Looking for troubleshooting advice. Thanks in advance. You guys are great.
Doug
N1235D - 1951 170A - SN: 20118
Re: Intercom Tone When Transmitting
Maybe you missed some isolation washers on your jacks ?
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
1953 C170B S/N 25656
02 K1200RS
Re: Intercom Tone When Transmitting
Yes, it might be a “ground loop” which commonly makes a “tone”.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Re: Intercom Tone When Transmitting
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
1953 C170B S/N 25656
02 K1200RS
Re: Intercom Tone When Transmitting
Thanks! I’ll double check and see if they are missing.c170b53 wrote:https://www.aircraftspruce.com/catalog/ ... gLjQfD_BwE
These guys
N1235D - 1951 170A - SN: 20118
Re: Intercom Tone When Transmitting
Well, I installed insulated washers on all of the pilot, copilot and handheld microphone jacks with no improvement. The rear headset jacks are on plastic so they are already insulated from the airframe.
So I’m not sure where to go next. The only other thing I touched as part of the updates is I replaced the com antenna coax cable because the old cable was rubbing and worn through to the shielding in one spot. Could a mistake on installing the new cable cause this tone?
So I’m not sure where to go next. The only other thing I touched as part of the updates is I replaced the com antenna coax cable because the old cable was rubbing and worn through to the shielding in one spot. Could a mistake on installing the new cable cause this tone?
N1235D - 1951 170A - SN: 20118
Re: Intercom Tone When Transmitting
Is the tone received by anyone to whom you are broadcasting?
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Re: Intercom Tone When Transmitting
gahorn wrote:Is the tone received by anyone to whom you are broadcasting?
Good question... I’ll check that today. I’m at a small grass airport that hasn’t been busy. When I have tested it.
N1235D - 1951 170A - SN: 20118
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- Posts: 13
- Joined: Wed Sep 05, 2007 9:53 pm
Re: Intercom Tone When Transmitting
Check that the new coax braid is connected at both ends. You could be getting RF into the mic audio circuit.
Re: Intercom Tone When Transmitting
Mike, when you say braid, you mean check the outer shielding? How would you test it?Mike Gourd wrote:Check that the new coax braid is connected at both ends. You could be getting RF into the mic audio circuit.
N1235D - 1951 170A - SN: 20118
- Bruce Fenstermacher
- Posts: 10320
- Joined: Tue Apr 23, 2002 11:24 am
Re: Intercom Tone When Transmitting
The braided shield should be grounded to the end fitting when crimped. Checking for continuity between the out side of one crimped fitting and the other would prove that both fittings contact the shield.
You should be able to pull the cable off one end and test continuity between the outside of the crimp and ground since the other side of the cable should be eventually grounded at the end of the run either at the radio or antenna.
If you don't get continuity at one end testing above. Take the test one step further and disconnect both ends of the cable. Connect your multi meter with long leads between each crimp. Don't have long enough leads. Use a jumper an one end or the other to jump the crimp to ground and then test the other side for continuity to ground.
You should be able to pull the cable off one end and test continuity between the outside of the crimp and ground since the other side of the cable should be eventually grounded at the end of the run either at the radio or antenna.
If you don't get continuity at one end testing above. Take the test one step further and disconnect both ends of the cable. Connect your multi meter with long leads between each crimp. Don't have long enough leads. Use a jumper an one end or the other to jump the crimp to ground and then test the other side for continuity to ground.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
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- Posts: 13
- Joined: Wed Sep 05, 2007 9:53 pm
Re: Intercom Tone When Transmitting
I agree with Bruce.
Re: Intercom Tone When Transmitting
Trying to add to what's already been said ...
In addition to a ground loop, I'd look for supply voltage disturbances or instability. Transmit draws a lot of current, so high resistance in the supply breaker or wire connections could do this, as could high ground resistance. The KX170B is an old radio with only one ground wire, so make sure all the new terminals you crimped are solid. Is the intercom ground point the same physical location as the radio? Did you change it?
Do you hear the noise in the NAV audio?
Is this occurring with the engine not running? If so, what's the battery voltage? What's the voltage at the output of the radio breaker? Can you change the frequency or volume of the noise by changing other electrical loads?
Is the new headset wiring shielded? Is it bundled with the antenna coax? What kind of cable is the antenna coax, RG-400? RG-58? Did you fabricate the cable and crimp the terminals yourself? Did you replace the right-angle chassis connector too?
Dave
In addition to a ground loop, I'd look for supply voltage disturbances or instability. Transmit draws a lot of current, so high resistance in the supply breaker or wire connections could do this, as could high ground resistance. The KX170B is an old radio with only one ground wire, so make sure all the new terminals you crimped are solid. Is the intercom ground point the same physical location as the radio? Did you change it?
Do you hear the noise in the NAV audio?
Is this occurring with the engine not running? If so, what's the battery voltage? What's the voltage at the output of the radio breaker? Can you change the frequency or volume of the noise by changing other electrical loads?
Is the new headset wiring shielded? Is it bundled with the antenna coax? What kind of cable is the antenna coax, RG-400? RG-58? Did you fabricate the cable and crimp the terminals yourself? Did you replace the right-angle chassis connector too?
Dave
Re: Intercom Tone When Transmitting
If the side tone just started it probably is not the jacks but it could be. I would check to see that you are grounding well. No more then 3 ground connections on any lug in avionics and also make sure that the battery ground to frame is good. no corrosion. grounding is the leading cause to avionics trouble. Also if it started after you touched something go back to that something and redo it. Good Luck.
52' C-170B N2713D Ser #25255
Doug
Doug
Re: Intercom Tone When Transmitting
Thanks, guys. I’ll dig deeper into the grounds and the shield on the new coax. Hopefully have some news by Wednesday if I can get free to head to the hangar.
N1235D - 1951 170A - SN: 20118