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Radio Noise problem solved

mark960

Active Member
I have been working with my neighbor trying to solve a radio static problem that had been hounding him for the past year or so. There was very strong static interference, that made reception nearly impossible. I had made multiple suggestions to try to help him narrow down the source with little results. I finally went up with him for a flight test in his plane and had the following results.


Background:
His aircraft is an RV-12 with the Garmin/Apollo SL-40 comm
It is the E-LSA version with the Rotax 912 ULS

Troubleshooting:
The radio noise was static (not a whine)
The static interference was sometimes strong enough to break squelch.
The static decreased if the engine power/RPM was reduced.
Tried turning off, and pulling fuses, for all other electrical devices, first one at a time then everything.
Pulled the fuse for alternator, with no change.
Turning off 1 ignition at a time resulted in a very minor change (but noticeable)
We did NOT turn off both ignitions in flight. (not willing to shut down engine)
Even with all avionics off, the static was present on a battery powered handheld radio.
If the handheld radio was moved towards the back of the aircraft, the static decreased.

Diagnosis:
Based on above, it pointed to ignition being source of static. The wires going from the ignition switches to the ignition are shielded and grounded at both ends. However, the assembly holding the ignition switches is open.

Remediation:
Removed ignition switch assembly and fabricated a metal shield to cover switches.
....Additional flight test showed a noticeable decrease in static but still significant
Replaced comm antenna RG-59 coax cable with RG-400

Results:
Comm static now to barely noticeable levels. HAPPY PILOT :)


SUMMARY
It is important to determine the source before proceeding. Prior to my fight test with him, it was thought to be the alternator. Multiple steps had been taken thinking it was the alternator, He had replaced the voltage regulator and installed a filter capacitor with NO change.

In the end, the problem was solved by shielding the panel ignition switch assembly and replacing the RG-59 coax with RG-400.

Possibly, replacing the electronic ignition may have solved the problem.
 
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I have been working with my neighbor trying to solve a radio static problem that had been hounding him for the past year or so. There was very strong static interference, that made reception nearly impossible. I had made multiple suggestions to try to help him narrow down the source with little results. I finally went up with him for a flight test in his plane and had the following results.


Background:
His aircraft is an RV-12 with the Garmin/Apollo SL-40 comm

Troubleshooting:
The radio noise was static (not a whine)
The static interference was sometimes strong enough to break squelch.
The static decreased if the engine power/RPM was reduced.
Tried turning off, and pulling fuses, for all other electrical devices, first one at a time then everything.
Pulled the fuse for alternator, with no change.
Turning off 1 ignition at a time resulted in a very minor change (but noticeable)
We did NOT turn off both ignitions in flight. (not willing to shut down engine)
Even with all avionics off, the static was present on a battery powered handheld radio.
If the handheld radio was moved towards the back of the aircraft, the static decreased.

Diagnosis:
Based on above, it pointed to ignition being source of static. The wires going from the ignition switches to the ignition are shielded and grounded at both ends. However, the assembly holding the ignition switches is open.

Remediation:
Removed ignition switch assembly and fabricated a metal shield to cover switches.
....Additional flight test showed a noticeable decrease in static but still significant
Replaced comm antenna RG-59 coax cable with RG-400

Results:
Comm static now to barely noticeable levels. HAPPY PILOT :)


SUMMARY
It is important to determine the source before proceeding. Prior to my fight test with him, it was thought to be the alternator. Multiple steps had been taken thinking it was the alternator, He had replaced the voltage regulator and installed a filter capacitor with NO change.

In the end, the problem was solved by shielding the panel ignition switch assembly and replacing the RG-59 coax with RG-400.

Possibly, replacing the electronic ignition may have solved the problem.

Mark, it would be interesting to hear some specifics about the RV-12 that had the problem. I.E., was it a standard build certified as an E-LSA or one with an alternate engine?

The reason for that is that with more than 700 RV-12's now flying, and the majority of them having been built as E-LSA (which means they are all virtually identical to each other and the certified S-LSA version), logic would indicate that this static problem should be quite prevalent on RV-12's.

My guess is that there was a problem with the ant. coax and by choosing to replace it with RG-400, it removed the problem.
 
Mark, it would be interesting to hear some specifics about the RV-12 that had the problem. I.E., was it a standard build certified as an E-LSA or one with an alternate engine?

The reason for that is that with more than 700 RV-12's now flying, and the majority of them having been built as E-LSA (which means they are all virtually identical to each other and the certified S-LSA version), logic would indicate that this static problem should be quite prevalent on RV-12's.

My guess is that there was a problem with the ant. coax and by choosing to replace it with RG-400, it removed the problem.

It is the E-LSA standard build version with the Rotax 912 ULS that the owner built to the specs. I too would have expected to hear of similar problems for other 12's.

The owner had contacted Van's multiple times and was unable to resolve the problem with them. He also had been to a Rotax dealer/shop in Sebring and they thought it was the alternator charging system at fault. They convinced him to replace the voltage regulator and install the filter capacitor. He had also been to a local avionics shop to check the radio, which tested OK. They too thought it was the charging system and had him install additional grounding straps that had no improvement.

Proper diagnosis is vital to determining the source of the problem. Unfortunately, the owner was not experienced in avionics and had difficulty in describing and diagnosing his problem. On the other hand, I have avionics experience from the military, at a general aviation avionics shop, and spent 30 some years teaching electronics and computers.

I did spend significant time inspecting the installation and did not see anything wrong. I did reroute the comm wires to the "magic box" and rerouted the antenna coax cable that was pushed up against the firewall. Maybe, there was a problem with that too. However, the interference that I picked up on the handheld, told me there was something more than just a problem with the avionics install.

I do suspect that the problem may be the electronic ignition boxes or improper installation of them. But again, I did spend time inspecting them and every thing associated with them and could not see anything wrong there.
 
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This is probably a typo but if it really did have RG59 coax, that is the wrong impedance for aircraft radios and antennas.
 
RG59 .. or RG58.. yikes..

My brand new RV-12iS came with a Nav antenna that had an RG58 coax/balun attached to it. I went through the trouble of scrapping it and rebuilding the assembly with RG142 (RG400 is arguably better since the stranded center conductor is happier during vibrations). Did it make a difference? I don't know.. but if I ever have problems, I know its definitely not shoddy coax cable.

IMHO, the only coax that should be used in aircraft is RG142/RG400 because of the superior shielding. (there's also better loss characteristics too, but our runs are so short and on such a low frequency, in real-life, that doesn't matter much). I tell everyone who is working on noise problems to trace each audio and RF cable.. diagram it.. note where the wire's shields are connected to, etc.. and make sure it is the best materials you can use, and replace if it is not.

After that, then you can start the real troubleshooting and narrowing down culprits.
 
RG59 .. or RG58.. yikes..

My brand new RV-12iS came with a Nav antenna that had an RG58 coax/balun attached to it. I went through the trouble of scrapping it and rebuilding the assembly with RG142 (RG400 is arguably better since the stranded center conductor is happier during vibrations). Did it make a difference? I don't know.. but if I ever have problems, I know its definitely not shoddy coax cable.

IMHO, the only coax that should be used in aircraft is RG142/RG400 because of the superior shielding. (there's also better loss characteristics too, but our runs are so short and on such a low frequency, in real-life, that doesn't matter much). I tell everyone who is working on noise problems to trace each audio and RF cable.. diagram it.. note where the wire's shields are connected to, etc.. and make sure it is the best materials you can use, and replace if it is not.

After that, then you can start the real troubleshooting and narrowing down culprits.


Yes, it was the 50 ohm RG-58. And yes, I did inspect it end to end for any nicks or deformities
 
Would be a **** shoot, but I noticed this comment in you initial post:

“The wires going from the ignition switches to the ignition are shielded and grounded at both ends.”

Proper practice is to ONLY ground one end of the drain/shield wires to minimize the chances for circulating grounds on these conductors. Worth a shot to lift one end and see if any results.
 
Would be a **** shoot, but I noticed this comment in you initial post:

“The wires going from the ignition switches to the ignition are shielded and grounded at both ends.”

Proper practice is to ONLY ground one end of the drain/shield wires to minimize the chances for circulating grounds on these conductors. Worth a shot to lift one end and see if any results.

Shielding on one end is typically done for audio circuits to prevent ground loops. (The electrical kind, not the tailwheel kind)

Rotax specifies that the shielding be grounded at BOTH ends. Even with that said, I did try disconnecting one end of the shield for both wires with no improvement.


Rotax Install copy by mark_960, on Flickr
 
Radio Noise problem

I have an ELSA RV-12 that I bought with 335 hours on it. I bought it from the second owner. It had a bad noise problem when I transmitted. I called the builder and asked him if he ever had the problem. He said once and he took the radio out, an SL-40, and sprayed the pins and socket with electrical cleaner. He let it dry and put back in and problem solved.

So I took the radio out, did the same thing. When I was putting it back, I realized that it had not been installed all the way into the tray. The set screw that turns it in had not been turned all the way. When I turned it in all the way so the radio was properly seated in the tray, the noise was gone.
 
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