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I'm hoping the list can help me with a radio transmitting problem.
I am a 3-month-new owner of an Ercoupe 415-C. My radio is an old ARC
Cessna 300 Nav Com. It came to me with the VOR inoperative, but the
radio sounded great.
But recently, it has developed a transmitting problem. Typically, before
starting the engine, if I do a radio check, Ground Control says my
transmission is either "fine" or "on the weak side, but readable." But
it deteriorates from there: once I've done a couple of touch-n-go
landings, the tower is asking me to repeat. After 2 more, they're
telling me my transmissions have become almost unreadable. For
shorthand, below, I will call this sequence the "Same Problem."
Problems first arose after I took off from Torrance, and was crossing
over the LAX Special Flight Rules Area, and another plane told me I was
unreadable, although I heard him fine. As I flew into Camarillo, I
think I lost all sound for about 5 seconds (behind a hill??), but it
came back, and I had no problem with the landing. However, on taxiing
to depart, Camarillo Ground could not hear me at all, although they were
loud & clear to me. When I changed to my back-up headset, they said
transmission was loud and clear, so I flew out. I had no complaints
from Torrance Tower when I landed back home.
Then an acquaintance who is an avionics man with Delta came out and
checked that headset against his, and said he thought the mic tip had
gone bad, so I've sent it in to Telex-Echelon to check it.
However, meanwhile, the next time I tried to fly, using the *backup*
headset, the pattern of "Same Problem" (deteriorating transmissions) began.
So I took it to an A&P, who first pulled the old Cessna 300 radio out of
its tray, cleaned all the connections, and put it back. I did a few
touch-n-goes, and the "Same Problem" developed. I landed and taxied
back to his hanger, shut off the engine, and gave him my hand-held
ICOM. He had me tune to 123.45 and talk to him: he said the
transmitting sounded fine with the engine off. Then I did a radio check
(engine still off) with Ground Control, and they said I sounded fine
(even though we were between hangars). So that caused him to say, "It
probably isn't the radio itself." We're kinda suspecting some engine or
ignition noise interference.
The next day, he checked & cleaned all the grounds, and checked the mag
noise filters for tightness; said one seemed a bit loose & tightened
it. I flew it again, but got Same Problem, same as the day before.
Today, an acquaintance (avionics man at Delta) came out with an ohmmeter
(sp?), pulled the radio from the tray, checked the antenna wire from
behind the tray, had me wiggle the antenna while he did this, and said
it's probably not the antenna wiring. He looked around the engine
compartment, found 1 wire whose covering was the old kind and crumbled
for about an inch; he taped that up.
All I've heard of that is left to check is to replace the mag noise
filters, and see if that solves it. I've ordered 2 new ones and if I
get the Same Problem the next time I fly, I will switch to using a
hand-held Nav-Com and will pick the mag noise filters up from Spruce on
Tuesday.
If new mag noise filters don't solve it, are there any other sources of
this kind of problem that I should check out before concluding I need to
buy a new radio?
Oh -- I'm ignorant of electronics, and nearly so about aircraft engines
(though learning fast, of necessity) so if you reply, please explain
acronyms or other verbal short-hand so you don't lose me in the dust ;-)
Thank you!
Linda
Ercoupe N3437H
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