I'm Going In... Radio Saga Continued...

Sidetone is, by definition, NOT the audio you hear when you receive. That's
the "received audio." Sidetone is you getting to hear yourself when you transmit.

The "sidetone" there is actually just the intercom functioning normally.

That all pretty much makes sense to me...

So it has always transmitted properly?

I'm pretty sure it has... I recall one of my first failures, while
shooting ILS approaches at SAC. After minutes of trying to figure out
why ATC wasn't responding to me, I grabbed my handheld to find out that
they had been hearing me all along. However, at that time, I was
hearing sidetone while xmitting, just not hearing audio back.

Here's something to think about based on my experience. Before we finished
the interior, we had a couple of intercom jacks in the back seats just zip-tied up,
but with bare 0.250/0.208 jacks wired in. Every once in awhile, they would move so
that in-flight the jacks would touch something aluminum. That would cause a really
ugly static, intermittent signal on the intercom if it hit a MIC wire. Between that
and the possibility of the intercom sharing multiple mics together, see if that adds
something to your debug equation.

I'm considering opening all of the intercom jacks (two in front and two
in back) and visually inspecting the connectors and wires there too,
just for grins. I'll pull new wire for them, if I have to as well...

"Fade out with scratchiness" sounds like it could be internal to the radio.

That's a tough one, because I don't even know if I'm describing this
symptom well... It's very quick and is simply an indication that the
failure is occurring. It's not a long drawn out fade, and the
scratchiness is really more of a quick (but barely audible) static that
I hear, when the radio fails.

Neither the thermal stresses nor the vibration are adequately simulated by
letting the thing warm on the bench for 5 hours. Do you have active cooling and is it
in good shape? i.e. a fan or ram-air blowing on it?

Not that I am aware of???

I hear you. Troubleshooting intermittent problems sucks. Another possibility
is wrong spacers on one or more trays. My mechanic had troubles with his transponder
and intermittent connections on an encoder line or two. After a bunch of rewires,
checking, etc, we discovered that some small nuts/washers were installed on the wrong
side of the connector on the back of the tray. It was preventing the connector from
seating an additional 1/8" and causing intermittent failures on a few pins.

That 1/8" issue is one of the top things in my mind... I'm thinking
the whole exercise of pulling, cleaning and reinstalling may enable me
to get a proper seating, that may not be occurring now???

From that right there, it sounds like you can rule out your radio. Don't
discount multiple *different* failures in the debug equation. Maybe it's your audio
panel or intercom?

Possibly???

RG-400 shouldn't really be necessary at VHF frequencies. The materials are
better, and it has better high-frequency characteristics (e.g. transponder or DME).
At VHF it primarily serves to be more of a PITA to work with (much more rigid). It
also screwed with my compass once because it had a copper/tin-clad steel center
conductor.

That's good to know... The RG-58 is much cheaper!

Thanks to you, and to all for your input! I feel like Chevy Chase, in
Fletch, when I'm looking at this stuff! I'm pretty darn sure the whole
problem is in the Fetzer Valve... Now if I can just round up some
gauze and some ball-bearings, I think I might be able to get this
problem licked! ;-) Ohhh, and I'll have to clean the windows too,
because they've got "filth muck" all over them!

Todd

Todd ...

Everybody here is trying to tell you the same thing in different words. You
have a "I'll just pull wire and everything will be all right" fetish. Get
over it. "Bad wires" have about as much chance for failure as "bad bolts".

My advice is to tune in a constant signal ... like an atis or awos and start
moving things around briskly. When the signal fails or comes back after
failure repeat the jiggle. Narrow down the jiggle area.

Jim



I'm considering opening all of the intercom jacks (two in front and two
in back) and visually inspecting the connectors and wires there too,
just for grins. I'll pull new wire for them, if I have to as well...


That's good to know... The RG-58 is much cheaper!

Everybody here is trying to tell you the same thing in different words. You
have a "I'll just pull wire and everything will be all right" fetish. Get
over it. "Bad wires" have about as much chance for failure as "bad bolts".

Okay, so I hear you... but I think where my fetish lies is not with
pulling new wires, but in making sure there is proper seating, in
anything and everything I can get to. If what I'm hearing is that Coax
and wires will have nothing to do with it, I will move on from that
thought. I was thinking corrosion, rust, ??? on a coax connector, or
connector anywhere (especially connector tray - radio), for that
matter. Even you agreed that replacing the coax "may work" and that I
would only be out a couple of bucks, worst case. Your description of
cutting the coax at a 45 degree angle led me to think that you might be
questioning the coax "connector" to radio or antenna or at least be
keeping it on a list of suspects.

My advice is to tune in a constant signal ... like an atis or awos and start
moving things around briskly. When the signal fails or comes back after
failure repeat the jiggle. Narrow down the jiggle area.

I've been using the ATIS at SAC as my constant signal, and have been
forcefully pressing the radio in and shaking it from side to side to
see if I can get it to come in, so much so that the LED's dim on the
radio as I'm pushing it in. That's never got reception to come back.
As far as other things, which I assume you are talking about wires
behind the panel, I can certainly give that a try, once I can figure
out how to do that without putting my self into an unintentional
unusual attitude. I'm 6'2" and about 2 bucks, so I can barely get
behind the panel when the plane is parked safely on the ground, let
alone 5000 feet and 100 kts.

I REALLY do appreciate all of the input, and am not TRYING to be a
knuckle-head about all of this! I'm just trying to interplote the
input I am receiving and do things that are within my capabilities.
And in this case, my capabilities don't seem to cover a very broad
spectrum!

Thanks,
Todd

three-eight-hotel wrote:
: Okay, so I hear you... but I think where my fetish lies is not with
: pulling new wires, but in making sure there is proper seating, in
: anything and everything I can get to. If what I'm hearing is that Coax
: and wires will have nothing to do with it, I will move on from that
: thought. I was thinking corrosion, rust, ??? on a coax connector, or
: connector anywhere (especially connector tray - radio), for that
: matter. Even you agreed that replacing the coax "may work" and that I
: would only be out a couple of bucks, worst case. Your description of
: cutting the coax at a 45 degree angle led me to think that you might be
: questioning the coax "connector" to radio or antenna or at least be
: keeping it on a list of suspects.

Coax isn't all that hard to replace, necessarily... BUT it can be a big pain
to route. It goes all the way to the antenna... likely a fairly long way. Soldering
the ends on (well) requires a pretty good knowledge of a soldering iron... not just
"which end to grab." Given that it's very unlikely to be that particular one, I'd
start with something else.

: My advice is to tune in a constant signal ... like an atis or awos and start
: moving things around briskly. When the signal fails or comes back after
: failure repeat the jiggle. Narrow down the jiggle area.

: I've been using the ATIS at SAC as my constant signal, and have been
: forcefully pressing the radio in and shaking it from side to side to
: see if I can get it to come in, so much so that the LED's dim on the
: radio as I'm pushing it in. That's never got reception to come back.
: As far as other things, which I assume you are talking about wires
: behind the panel, I can certainly give that a try, once I can figure
: out how to do that without putting my self into an unintentional
: unusual attitude. I'm 6'2" and about 2 bucks, so I can barely get
: behind the panel when the plane is parked safely on the ground, let
: alone 5000 feet and 100 kts.

The problem my mechanic's transponder had couldn't be induced by forcing the
radio around in the tray. It was a mechanical stop near the connector. Couldn't
really make it come and go. Of course it was further complicated by the fact that the
only way to check it was to test-fly it and ask local ATC if they could read ModeC (I
don't have a transponder interroagtor). For your COM, it should be easier.

Just as a thought... have you tried pulling out the squelch when you're unable
to receive? If you don't hear static when you can't receive, it's likely in the
wiring/connector from the radio/intercom/audiopanel/jacks. If you hear static but you
still cannot receive, then it's much more likely the radio.

: I REALLY do appreciate all of the input, and am not TRYING to be a
: knuckle-head about all of this! I'm just trying to interplote the
: input I am receiving and do things that are within my capabilities.
: And in this case, my capabilities don't seem to cover a very broad
: spectrum!

The biggest thing would be to try and make it happen on the ground so that you
can troubleshoot it. I'm not familiar with Narco's trays, but on the King ones, the
connector can be disconnected from the tray. Then you could play with that without
being stuck with the geometry of the tray. Basically, stop at the top and work
down...

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

I was thinking corrosion, rust, ???

Rust is iron oxide and will only form on iron or steel. Corrosion is a
different matter, but you can rub or spray corrosion off. The only way coax
deteriorates is in sunlight or with water inside the shield. Age is a
second order factor.




on a coax connector, or
connector anywhere (especially connector tray - radio), for that
matter. Even you agreed that replacing the coax "may work" and that I
would only be out a couple of bucks, worst case.

Yeah, as well as throwing salt over my left shoulder has kept me from being
trampled by hippopotami all my life, but I don't think replacing the salt
shaker is going to have any effect.



Your description of
cutting the coax at a 45 degree angle led me to think that you might be
questioning the coax "connector" to radio or antenna or at least be
keeping it on a list of suspects.

No, I was telling you to do that so the square-cut coax wouldn't hang up on
the grommets as you pulled it.





My advice is to tune in a constant signal ... like an atis or awos and
start
moving things around briskly. When the signal fails or comes back after
failure repeat the jiggle. Narrow down the jiggle area.

I've been using the ATIS at SAC as my constant signal, and have been
forcefully pressing the radio in and shaking it from side to side to
see if I can get it to come in, so much so that the LED's dim on the
radio as I'm pushing it in.

Do you intend to destroy your radio in the fixit process?



That's never got reception to come back.
As far as other things, which I assume you are talking about wires
behind the panel, I can certainly give that a try, once I can figure
out how to do that without putting my self into an unintentional
unusual attitude. I'm 6'2" and about 2 bucks, so I can barely get
behind the panel when the plane is parked safely on the ground, let
alone 5000 feet and 100 kts.

You CANNOT do troubleshooting at 5K and speed. You HAVE to do it on the
ground. THe easy way is to pull the front seats out and lay on the floor.
I'm 6-3 and two and a quarter, and this is the only way I can troubleshoot
any airplane except a heavy with a radio rack in the belly.




I REALLY do appreciate all of the input, and am not TRYING to be a
knuckle-head about all of this! I'm just trying to interplote the
input I am receiving and do things that are within my capabilities.
And in this case, my capabilities don't seem to cover a very broad
spectrum!

You need to get the airplane to a place where you can get at the radio with
a constant signal. You also need access to tools and such when you DO find
the problem. I think I've got an old com test set around here somewhere
that radiates a constant low level signal on 122.8, powered by a 9 volt
battery. If you'd like to come up to Grass Valley and borrow it, I'd be
glad to loan it to you ... if I can find it.

Jim

Just a (dumb?) question to the OP: Does the radio tray have a BNC connector
for the coax cable connection? Can you try a piece of short coax connected
to a 'portable' antenna attached to some type of ground plane? If this setup
works, then you'll know it's somewhere in the original coax connections, if
the radio still doesn't receive, then it would be a different connection
problem.

Are you sure the radio itself is good?

If you have already tried this, disregard...