VHF radio in Avid with 582 2 stroke
We are trying to get a vhf radio to work in our Avid heavy hauler, 582 blue head.
In my experience when having radio problems it is in the recieve.
We are having a problem in the send.
We have a "normal" installation with the electrical components that came with
the new engine, new regulator, plugs wires and caps.
Recieve is loud and clear but when we transmit all we send is a loud squealing
sound with a barely readable voice.
We tried several radios, all handhelds, and all were the same
We tied two different antennas in two different location still no joy.
I read thru the Avid forum and one of the items mentioned was shielded wires to the
mag kill switch, did it, still no change.
Others mentioned getting rid of the resistor plug caps?
I have considered replacing the copper core plug wires with carbon core?
It is not a variable rattling noise like it would be if it was spark plug
The next thing I might try is a new regulator and then stator. Expensive.
It makes no difference if it is plugged into A/c power or on it's own battery so
it is not coming thru the wires.
When I move the handheld away from the airplane at about midwing it is better,
at the wingtips it is fine, so it is definately RF interference.
We have a metal firewall so whatever it is (is) strong enough to overcome that
The only thing in the cockpit is the Tinytac and unhooking it was no help.
Help is what I need, suggestions would be appreciated.
- Is the problem present only when the engine is running, or any time the radio transmits near this aircraft's fuselage?
- Are you using rubber-duckie type antennas on the handhelds, or fixed type installed in the aircraft?
If your antennas are fixed type:
- When you swapped antennas, did you also change the coaxial cable (and BNC adapter, if you're using one)?
- Is the coaxial cable routed away from, and not bundled together with, other electrical wiring?
Interference is there only when engine is running, used both rubber ducky antenna and brand new aircraft mounted antenna. Coax was tied under the dash but removed and led out the door for the distance to engine test.
When the engine is not running it is 5/5. I have tried transmitting just as I shut down the engine and the interference disappears when the engine stops, not when the mags are shut off, still noisy as the engine is running down
Has any one had a problem with the charging system putting out stray rf. It does not seem to be RPM related.
I think you're on the right track with regard to the source. If it doesn't stop the instant the mags are shut off, it can't be ignition related. That leaves the charging system, especially given that it continues until rotation stops.
You could confirm the charging system as the source by running the engine with the alternator belt removed, or the alternator field wire disconnected. If disabling the alternator stops the noise, that's it. As for exactly where the RF is radiating from, hopefully someone who's experienced this same problem will chime in.
Perhaps there's a cable in the charging system somewhere that's at a tuned length in the VHF air band? I'm grasping at straws here -- my knowledge of RF theory is confined to radar, and it's nearly 20 years old.
Double-check all the ground points in the charging system too. A loose or corroded ground can generate noise.
Mags still produce electrical energy until the engine completely stops. When you shut the mags "off" you are simply providing that energy an alternative path to ground... directly to the airframe, rather than across the spark plug gap. It may be a bad capacitor/condenser in one of the mags. Also, I would try pulling the alternator field breaker to test whether or not it's the charging system. An AM radio can help pick up an identify the interference source(s). If you find the source you can try using shielded wire on that system if possible.
first off, Ray, i'll admit i am NOT a radio tech or electronics guru. just a guy who had an avid with 532 so i read your post. but i am knowledgeable enough to know you don't have an alternator belt to disconnect, nor a field wire you can find easily, nor magnetos to dink with. and cautious enough not to try starting the engine with the voltage regulator disconnected to avoid letting the smoke out of the electrical system someplace.
Originally Posted by raytoews
i did not have shielded wire to the kill switch, used the "stock" plug caps and wires and a narco 870 handheld with rubber ducky antenna on it, on the panel, with a home-made radio adapter. rx fine, tx had a squeal in it, readable but very annoying and lousy tx range. tried shielded wire to kill switch, then shielding ignition, then switching plugs and plug wires and plug caps etc, no significant change. switched to remote antenna on panel over baggage compartment, slight improvement in tx range and no squeal. finally switched to panel-mount to get better range, got it, still no squeal.
short answer, ignition etc that "everybody" said was the problem - wasn't. don't know what was.
you're using handhelds - no panel mount at all, right? what microphones? the ones in the handhelds, or do you have an adapter plugged in? who made adapter, radio guys or homemade? same adapter and mic every time? you said "two different antennas in two locations no joy" but "move the handheld away from the airplane at about midwing it is better, at the wingtips it is fine". you might try temporarily cabling the antenna out there on a ground plane?
in other words, i don't know either. good luck on finding somebody who knows two-strokes and radios.
Have you tried by-passing the headset/intercom for test purposes by transmiting just pressing the PTT on the radio whilst its in the a/c,
Is your antena grounded to the a/c metal frame,
I remember I used to get a howl on transmit got rid of after powering my intcom from a seperate small 12v battery,
I wonder how good your anntena system is ????