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Poor Radio Quality on one Freq, one radio

bill.hutchison

Well Known Member
I've got two radios in my RV - an SL-30 and a GNC 250XL GPS/Comm.

We're required to talk to departure at my field, and there is one frequency which always, always sounds terrible in my ears when I transmit on the SL-30. Scratchy and staticky. (125.12 out of VKX, if you're interested.)

Doesn't do that on any other frequency on that radio or on the other radio. It's just that freq on that radio.

The noise only appears to be on my side - ATC says it sounds fine on their side. It's not my headset, either - I've verified it with a Lightspeed Zulu, a QT Halo and a CQ. Same behavior on all.

What could cause that kind of noise on just one frequency on one radio?
 
SL-30

Bill, The SL-30 has a service Bull which I think is for this type of problem, not sure. It's a $1000 fix at Garmin ( I think ).

Also, I have a problem on my radios (both) about 3 miles off the end runway 11 that seems to block out communication with approach ( acts like a strong carrier blocking all communications) ( 1 mile in diameter ). Tracked it down to a hospital with MRI and CT. They charge "coils" in MRI's between 100Mhz and 300Mhz ( might be older systems that cause this) Hmmmm don't we operate in the same freqs. Have flown over other "MRI's" and this did not happen.

Take off on 24, fly 2 miles, yep, a hospital.

OK, it's probably the Garmin service Bull. John
 
I have had a similar problem with my SL-40. At some locations, I regularly have terrible static on 132.2 Oakland Center. This is at 10.5K, so doubt it is something on the ground. One time I had a similar issue on one other frequency during an XC, toward the outer reaches of that transmitter. As soon as I was handed off to a new sector, reception was good.

Back in the day, one might assume that if one frequency was bad, you had a bad crystal. Nowadays, hard to imagine a digital tuner having an issue with just one frequency.

Maybe I'll call Garmin. Step one might be to swap out for a different SL-40 and just try it.
 
HELP PLEASE . . . ...

I have the same issue PAR100EX, 123.000 only one location, Burlington, IA airport KBRL.

It sounds like music barely making it but it is strong enough to prevent communications. This flight, with the 650 on approach freq and the PAR on CTAF 123.00, it was so bad I could not contact ATC.

I really don't know how to go about understanding if it is an airframe, specific radio, or some ground based issue with broadcast.

KBRL Airport manager not interested helping - SteinAir said call Garmin :mad: and PSEngineering was not specific about how to better define the issue but said "not my radio" even though their name is on it. He even thought it might be an installation issue. 200 hrs, only place its happened. 2 yrs ago and this week, same location.

Is bad form to listen to both radios at the same time? Interference? Harmonics (what freq) digital broadcast - freq??

OH BTW - I found the FCC site to search for licenses geographically and by frequency. There is nothing in 10 miles of the airport between 120 MHz and 125 MHz except the airport license for CTAF
 
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I have the same issue PAR100EX, 123.000 only one location, Burlington, IA airport KBRL.

It sounds like music barely making it but it is strong enough to prevent communications. This flight, with the 650 on approach freq and the PAR on CTAF 123.00, it was so bad I could not contact ATC.

I really don't know how to go about understanding if it is an airframe, specific radio, or some ground based issue with broadcast.

KBRL Airport manager not interested helping - SteinAir said call Garmin :mad: and PSEngineering was not specific about how to better define the issue but said "not my radio" even though their name is on it. He even thought it might be an installation issue. 200 hrs, only place its happened. 2 yrs ago and this week, same location.

Is bad form to listen to both radios at the same time? Interference? Harmonics (what freq) digital broadcast - freq??

OH BTW - I found the FCC site to search for licenses geographically and by frequency. There is nothing in 10 miles of the airport between 120 MHz and 125 MHz except the airport license for CTAF


It is likely intermodulation caused by two or more radio signals, shows up at the sum and difference of the mixing frequencies. Difficult to track down and not much can be done about it as the sources can be operating within the requirements of the FCC, outputting clean RF signals and still cause interference.

Other types of interference can occur when flying in areas of powerful transmitters, for example, typical FM radio stations have ERP’s (Effective Radiated Power) well over 100 KW, plenty to overload the receiver.
The quality of receiver selectivity is important to prevent adjacent RF signals from overwhelming the receiver but it becomes very difficult to overcome with power levels of 100 KW.
 
It is likely intermodulation caused by two or more radio signals, shows up at the sum and difference of the mixing frequencies. Difficult to track down and not much can be done about it as the sources can be operating within the requirements of the FCC, outputting clean RF signals and still cause interference.

Other types of interference can occur when flying in areas of powerful transmitters, for example, typical FM radio stations have ERP’s (Effective Radiated Power) well over 100 KW, plenty to overload the receiver.
The quality of receiver selectivity is important to prevent adjacent RF signals from overwhelming the receiver but it becomes very difficult to overcome with power levels of 100 KW.

So true. It reminds me of our diamond of diamonds inbound for a very important missing man over the Air force Academy in CO not so long ago, fully listening to country music for a couple of miles on every pass of the staging position.

RIP Falcon.
 
It is likely intermodulation caused by two or more radio signals, shows up at the sum and difference of the mixing frequencies. Difficult to track down and not much can be done about it as the sources can be operating within the requirements of the FCC, outputting clean RF signals and still cause interference.

Other types of interference can occur when flying in areas of powerful transmitters, for example, typical FM radio stations have ERP’s (Effective Radiated Power) well over 100 KW, plenty to overload the receiver.
The quality of receiver selectivity is important to prevent adjacent RF signals from overwhelming the receiver but it becomes very difficult to overcome with power levels of 100 KW.

The FCC license search site by geography has one tower located where the interference was the worst in a previous flight. It broadcasts at 161.67MHz and 425.xxxMHz. The power is listed as 100 and ERP of 200 got for the former, but I can not find the units. Are these kW? If so, I think this might be my source. This tower is right in the vicinity where the interference was the most intense.

Now for some investigation with the FAA contract flight crews about their findings.
 
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