RF interference issue again (esp. for E Drucker and Jim Weir and other RF wizards)

Mark Mallory wrote in message ...

I would try disconnecting *all* the antennas on the plane except
for the *good* com's (and the transponder's)

Well, but.. which is the good com? They both get the interference..

If you get the impression I'm not too thrilled about disconnecting
all the antennae in the plane, you got that right. Removing
avionics and leaving them on the ground is easy, for the most part
(and legal for me to do AFAIK).

Disconnecting some of our antennae is a cast-iron b**** and
reconnecting them is worse. Notably, the VOR/glideslope antennae.
Which brings me to ask...what does d/c'ing antennae get me that
removing their avionics doesn't?

I'm really hoping to hear from a couple of other folks on this
one, notably Jim Weir since I took his advice, drove to the antenna
farm, and found interference w/ my handheld.

What do you suggest next, Jim?

Yes, I mentioned this in my first post... get in contact with their
Engineering Department and explain the problem. They'd be *more*
than interested, they're technically qualified guys, and they have
the necesssary equipment.

Well, I did. I can't say they were "more than interested" in fact,
they were initially interested in telling me my equipment was at
fault because "we just had our equipment checked last Tuesday and
we're absolutely clean".

But I'm hopeful I eventually persuaded the guy I talked to
that if I could drive up to the foot of other antenna and just get
some strong RF noise on the aviation band, but drive up to the
foot of his tower stick the ducky out the window and listen to
a broadcast 5x5, maybe this bore investigation. At least he said
he'd call me back in a couple days and gave me his direct number.

We'll see...

Cheers,
Sydney

Pull the darned radios. If the interference goes away, you at least know it was
ONE of the radios that did it. If you have dual coms, pull one, go fly, then
pull the other one, put the first one in, and go fly.

Jim




(Snowbird)
shared these priceless pearls of wisdom:

-I'm really hoping to hear from a couple of other folks on this
-one, notably Jim Weir since I took his advice, drove to the antenna
-farm, and found interference w/ my handheld.
-
-What do you suggest next, Jim?
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

On Mon, 10 Nov 2003 16:35:28 -0800, Jim Weir wrote:

Pull the darned radios. If the interference goes away, you at least know it was
ONE of the radios that did it. If you have dual coms, pull one, go fly, then
pull the other one, put the first one in, and go fly.

Jim

And if they're the same radios, switch trays, too.



(Snowbird)
shared these priceless pearls of wisdom:

-I'm really hoping to hear from a couple of other folks on this
-one, notably Jim Weir since I took his advice, drove to the antenna
-farm, and found interference w/ my handheld.
-
-What do you suggest next, Jim?
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Roger Halstead wrote:

On Fri, 07 Nov 2003 12:39:37 -0800, Jim Weir wrote:

Back in the old days we did it by trial and error and glommed onto what worked
best. When the digital computer came along, we got a full blown printout of the
inter/cross/spuri mod products across a frequency band and picked a
frequency(ies) for the IF that produced minimum spurious products.

Note the word MINIMUM. There has never been a receiver produced by the
superheterodyne process that is totally free of spurious, including the
magnificent Collins S-line or 51J series of receivers.

And they were tube type equipment which I think did far better at
rejecting intermod than transistors. OTOH todays FETs are pretty good.

Of course a miser is a mixer is a mixer ... which was designed to mix
the signals. It takes sojme careful design to prevent unwanted signals
from getting into (and out of) the mixer.

As you say, none of them are perfect.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)



I am sorry that I missed the beginning of the thread.

The King KX170 series is an excellent, if old, radio; and should be able to
regect the FM and VHF-TV band signals from as near as a couple of miles.

Nonetheless, your problem sounds like "front end overload" which is made
worse if the receiver has become slightly detuned over time. Therefore,
even though I usually assert that at least 80% of radio problems are really
antennas and other airframe wiring, I really thing that you will end up
sending the KX170 to the shop in order to solve this problem.

Peter

On 10-Nov-2003, (Snowbird) wrote:

Well, but.. which is the good com? They both get the interference..

If you get the impression I'm not too thrilled about disconnecting
all the antennae in the plane, you got that right. Removing
avionics and leaving them on the ground is easy, for the most part
(and legal for me to do AFAIK).

Disconnecting some of our antennae is a cast-iron b**** and
reconnecting them is worse. Notably, the VOR/glideslope antennae.
Which brings me to ask...what does d/c'ing antennae get me that
removing their avionics doesn't?

I'm really hoping to hear from a couple of other folks on this
one, notably Jim Weir since I took his advice, drove to the antenna
farm, and found interference w/ my handheld.

What do you suggest next, Jim?


Sydney,

What your drive to the antenna farm (with the handheld) "proved" is that the
problem is still most likely garden variety intermodulation interference.

Sure, go ahead and pull your radios one at a time as Jim Weir suggests. My
guess is that you will still have the problem on the remaining radio(s).
This is because each radio is generating its own intermodulation products.
But PLEASE don't start yanking antennas. As you note, they are a b***h to
deal with, and it is EXTREMELY unlikely that they are the source of the
problem based upon the symptoms you describe.

Oh, by the way, something that I don't think has been covered in this thread
(and I admit I haven't read every post): Broadcast signals are often much
stronger in some directions (from the broadcast antenna) than others. So,
if you are doing repeated flying tests they should be conducted in the same
location, not just the same distance from the antenna farm.



Well, I did. I can't say they were "more than interested" in fact,
they were initially interested in telling me my equipment was at
fault because "we just had our equipment checked last Tuesday and
we're absolutely clean".

But I'm hopeful I eventually persuaded the guy I talked to
that if I could drive up to the foot of other antenna and just get
some strong RF noise on the aviation band, but drive up to the
foot of his tower stick the ducky out the window and listen to
a broadcast 5x5, maybe this bore investigation. At least he said
he'd call me back in a couple days and gave me his direct number.

I would be VERY surprised if the interfering signals are being generated at
the antenna farm. Of course, as they say, "nothing is impossible."
--
-Elliott Drucker

How are we doing on this now by the way?

Paul

wrote in message
...
What your drive to the antenna farm (with the handheld) "proved" is that
the
problem is still most likely garden variety intermodulation interference.

"Paul Sengupta" wrote in message . ..
How are we doing on this now by the way?

Thanks for asking!

Well, DH set out on an "interference hunt" primed to
selectively remove this and that from the plane -- and
couldn't find any interference to remove. Haven't
run into any since.

So troubleshooting is on hold until the trouble shows
up again -- the reason intermittant problems are such
a bear.

Sydney

Ah. Maybe they've cleaned up the transmitter? Too much to
hope I guess...

Paul

"Snowbird" wrote in message
om...
Well, DH set out on an "interference hunt" primed to
selectively remove this and that from the plane -- and
couldn't find any interference to remove. Haven't
run into any since.