SV-COM-T25 transmission unreadable on 124.4

[Tsabean]

Recent problem reported by ATC. Radio is loud and clear on most frequencies but they report transmission garbled and strength one on 124.4 and 123.7. I can read ATC fine on those frequencies.

 

[Rhino]

Check your antenna, antenna cable and the connectors. If the cable isn't RG-400 or better, you should consider upgrading it. Too many builders make the mistake of using something cheap, like RG-58. If someone else has an antenna you can try temporarily, that might help you determine if your antenna is going bad. Also make sure the antenna is sealed well against the elements. Antenna sealant tends to break down over time, and that can be death for an antenna.

 

[jakej]

Rhino, you forgot another critical item = “electrical bonding“ of the antenna to airframe or ground plane .

 

[Rhino]

Rhino, you forgot another critical item = “electrical bonding“ of the antenna to airframe or ground plane .

I was sort of including that in "Check your antenna", but that's a good point.

 

[GKC Aviation]

Do you have an ELT antenna on your aircraft?
I have seen reports of harmonics between the two antennas causing transmission problems on certain frequencies

 

[Tsabean]

Check your antenna, antenna cable and the connectors. If the cable isn't RG-400 or better, you should consider upgrading it. Too many builders make the mistake of using something cheap, like RG-58. If someone else has an antenna you can try temporarily, that might help you determine if your antenna is going bad. Also make sure the antenna is sealed well against the elements. Antenna sealant tends to break down over time, and that can be death for an antenna.

Ok, will check the type of coax I used. Removed, cleaned contact points, and reinstalled antenna. No change.

 

[Tsabean]

Do you have an ELT antenna on your aircraft?
I have seen reports of harmonics between the two antennas causing transmission problems on certain frequencies

Thanks for the ELT hint. A local shop mentioned this may be an issue. Will Ryan and check this today.

 

[Tsabean]

Thanks for the ELT hint. A local shop mentioned this may be an issue. Will Ryan and check this today.

Finally got a weather window to fly. Removed the ELT and now loud and clear on all frequencies.

 

[Guenin]

Do you have an ELT antenna on your aircraft?
I have seen reports of harmonics between the two antennas causing transmission problems on certain frequencies

Radio newbie here: I'm genuinely curious as to why that might be. Aren't their frequency ranges (and therefore antenna lengths) sufficiently different that that wouldn't be a factor? And does that happen even if the ELT is silent? I've been having some comm receptions problems myself that I'm trying to troubleshoot. My comm antennas and my ELT antenna are about 3 feet apart.

 

[Rhino]

Many of the newer ELTs have GPS built into them, and that's the primary reason why this issue exists. GPS antennas near com antennas can also cause the same problem, because even passive GPS antennas can have active elements that produce RF. Although they are not the same frequency range, their harmonics often can be, especially if antennas are in close proximity. Manufacturers typically put minimum separation requirements in their installation manuals for that very reason. 3 feet should be plenty of separation, and I can't recall seeing anything over a 12 inch minimum on small aircraft. These problems typically show up when transmitting rather than receiving, though the latter is not totally out of the question.

 

[Guenin]

Ah, ok. My ELT must be an older one since it relies on my ship's GPS for its position. (ACK E-04). So I guess that's not contributing to my comm reception problems. Good to know.

 

[Rhino]

In your case, I would try powering everything down except the radio, and see if that fixes the problem. If it does fix it, try powering up the other devices one by one to help narrow down the culprit. If powering everything else down doesn't fix your problem, it's very unlikely that other equipment is causing your problem.

 

[GKC Aviation]

Because the ELT antenna is naturally resonant at 121.5 Mhz, it can cause harmonics on your transmissions at certain frequencies.
It's not all ELT's, and doesn't seem to matter about how close or far away your antenna is to the ELT antenna. Nor does it matter if you disconnect the ELT from the antenna, still does it.
I know it has frustrated people for a long time before someone tried removing the ELT antenna
VHF antennas connected to a radio don't cause this problem, it causes other problems if they are too close to each other.

I remember years ago struggling with getting a HF radio to work on a Bell Jetranger. We had the long wire antenna parallel to the boom (but not close to it), and the tail rotor drive shaft (being steel) was causing the transmission signal to be completely blanked. We moved the wire attach end by about 6 inches, giving it a slight angle away from parallel to the TR shaft, and it worked perfectly.

 

[Rhino]

An ELT doesn't transmit if it isn't activated. That's what I always found so weird about this.

 

[GKC Aviation]

I know...
Radio is weird sometimes and doesn't make sense