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.
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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