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

Blimey, thanks. Any idea how they decide to use these figures? Just out of
curiosity.

Paul

"Jim Weir" wrote in message
...
Nope. They are all over the map. I chose a random book from the
library...it
happens to be the King KX-170B. The high COM IF is 9.0M and the low COM
IF is
861.25k. The high NAV IF is 15.1875M and the low NAV IF is 1.1857M. I
could
pick half a dozen books from the shelf and no two would be the same.

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.

Jim



"Paul Sengupta"
shared these priceless pearls of wisdom:

-Blimey, thanks. Any idea how they decide to use these figures? Just out of
-curiosity.
-
-Paul
-
-"Jim Weir" wrote in message
.. .
- Nope. They are all over the map. I chose a random book from the
-library...it
- happens to be the King KX-170B. The high COM IF is 9.0M and the low COM
-IF is
- 861.25k. The high NAV IF is 15.1875M and the low NAV IF is 1.1857M. I
-could
- pick half a dozen books from the shelf and no two would be the same.
-

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

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 operate out of St Louis Regional and have noise on 126.00 on a KX170B.
--
Gene Seibel
Hangar 131 - http://www.pad39a.com/gene/plane.html
Because I fly, I envy no one.


Do other aircraft report the same interference?

Not that I've heard, but then, I might not have heard.
Or, like us, they might have assumed it was a problem in
their airplane.

We didn't have this problem before last spring.

Any assistance sorting this out would be greatly appreciated;
we do have a pretty good local avionics guy but he frankly
seems stumped (at least he's honest and good enough not to
simply suggest replacing all the radios in the stack, which
one shop did).

Cheers,
Sydney

("David Lesher" wrote)
snip
Well, first fly the handheld in another airframe. That establishes
iffen it's part of the solution or the precipatate.

If all's clean in that case, start looking at all grounds on yours.
Disconnect the easy antennas first.... and see if anything changes.
Keep good notes!

If all else fails...http://www.spacemodel.com/pic355.html


I've been fascinated with this thread. I'm following the discussion without
really understanding what it is I'm following ...but I'm able to follow it -
sort of.

I was going to offer my advice (a while ago) based on my boat trailer
experience - when in doubt, it's the ground. When you think you've cleaned
up the ground, replace the ground wire. When you've done that, make yet
another (fresh) ground connection, etc.

We took a friend's little 4x8 (utility) trailer out to SoDak this fall, when
we went pheasant hun'n. We were having all kinds of lighting problems with
that darn trailer before we left. He was very big into diagnosing the
problem. I ran 5 ft of fresh ground wire from the minivan tail lamp socket
to the trailer plug - making two (new) fresh ground connections along the
way. Lights worked fine. Double-grounded the trailer side of the plug with
new wire too - just in case. (20 minutes)

He wanted to know what it is I did, technically speaking. My answer - I'm
not exactly sure, but it always seems to do the trick.

--
Montblack

("Paul Sengupta" wrote)
Some people have reported picking up radio on their
fillings in their teeth.

http://www.tvtome.com/tvtome/servlet...d-599/season-2

Second season (In Color)

46. Hi-Fi Gilligan

Gilligan's mouth becomes a radio after he is accidentally hit on the head.
When their regular radio is broken, Gilligan becomes their sole source of
information on the approaching typhoon.

b: 25-Nov-1965 w: Mary C. McCall, Jr. d: Jack Arnold


--
Montblack

OK, so this afternoon I took my trusty ICom aviation handheld,
suction cupped its duckie to the windshield of DH's car, and
off we went

Going on an Antenna Hunt
Gonna Catch a BIG One
Sorry, too much before-bedtime reading to the toddler *g*

What we learned:
*our handheld ain't exactly a precision filter. I could
hear things like the turn signal and the electric windows
rolling down. power lines -- tcccchhk!
*nevertheless, we could hear aircraft on 126.5, and occasionally
(faint) the tracon
*adjusting so that such transmissions broke squelch but at
least some of the dreck was filtered out, we sure could tell
when we got close to them big antennae. RF interference up
the Ying Yang no ifs ands or buts
*TV Channel 2 antenna was the big winner. Where the other
big antennae just produced noise, I could sit near the
base of the Channel 2 antenna and listen to a program about
college football. Further out, came through in snatches. Right
there by the antenna, came through 3x5 on 126.5 and 5x5 on 127.0
*Didn't have time to fly and conduct the obvious experiment of
leaving Mr Handheld on the ground
*Now here's where it gets wierd: according to the TV schedule,
channel 4 and Channel 5 were broadcasting college football.
Channel 2 was showing a movie. Didn't have time to stay and
listen until we got a station identification. From what I
heard, sounded like Channel 5.

Will try to return to confirm lat-long of antenna (foolishly
didn't take my GPS along, though I think I have them straight)
and to get station ID if I can. Also trying to reach Channel
2 to see if they changed programming -- they're the station
which carries Mizzou football and might conceivably have
altered programming to carry football at that time.

Soooooooo Guri, what does *this* tell us?

What is TV channel 2 digital sound frequency and normal
Channel 2 sound frequency? Just wondering if by chance
the difference between the two might be...127.0?? How
about Channel 2 and Channel 5?

Jim Weir wrote in message . ..
Well, then take other folks advice who have had this problem and solved it. I
gave you the method that works for me.

I take my hat off, then Jim. I could barely scrape up the
hour to drive around, much less weeks or days or even hours
to park patiently. We're going to have to get at this by
pragmatic combinations.

-If I drive to the antenna farm and get the interference,
-does it prove the problem is outside my plane, or just that
-the handheld is also more susceptible to it?

It proves that the problem is outside your aircraft.

But....does it? The handheld is normally *in* my aircraft.
Albeit, it is normally disassembled from the battery pack
and with the ducky antenna disconnected from it.

And..what about the testimony of the DE that she flies in
lotsa planes in that area all the time and never heard that
problem before?

why I suggested that you find a friend that lives close to the farm

No such critter alas. We live about as close to it as anyone we
know.

-How could my nav radios (or my handheld) be contributing
-to this problem when they are *powered off*?
good explanation snipped
If any of these
"spurious mixer products" falls within the passband of the nav input filter,
it will be reradiated out the nav antenna directly into your com antenna.
...
Did that help?

Yes, thank you! That was very clear.

But just to confirm: what I'm hearing is that frequencies can
mix and be reradiated by a turned-off radio, *but they need an
antenna* to get anywhere? ie, if the ELT is in the plane but
disconnected from the antenna, it's not likely the source of
the problem...likewise, if the portable nav/com is disconnected
from its antenna?

Have we likely absolved my plane at this point?

Sydney

Snowbird wrote:

*TV Channel 2 antenna was the big winner. Where the other
big antennae just produced noise, I could sit near the
base of the Channel 2 antenna and listen to a program about
college football. Further out, came through in snatches. Right
there by the antenna, came through 3x5 on 126.5 and 5x5 on 127.0
*Didn't have time to fly and conduct the obvious experiment of
leaving Mr Handheld on the ground

*Now here's where it gets wierd: according to the TV schedule,
channel 4 and Channel 5 were broadcasting college football.
Channel 2 was showing a movie. Didn't have time to stay and
listen until we got a station identification. From what I
heard, sounded like Channel 5.


This makes sense! ...a possible intermod scenario (see my other post) is the
ch.4 aural carrier (71.75) mixing with the ch.2 visual carrier (55.25) resulting
in a product at 127.0 MHz. If the mixing were occuring in ch.2's visual xmtr,
IT would be the source of the 127.0 signal (even though the audio you hear is
coming from ch.4's xmtr, some distance away.)


-If I drive to the antenna farm and get the interference,
-does it prove the problem is outside my plane, or just that
-the handheld is also more susceptible to it?


It could mean:

The antenna farm is clean; the handheld and your plane *both* have a problem.

or,

The antenna farm has a problem; the handheld *may* be clean and your plane *may*
be clean.

Since you don't have enough information to distinguish between the above cases,
you can't rule your plane IN or OUT. On the other hand, if you HADN'T gotten
the interference on the ground with the handheld, you could probably rule the
plane IN (but still not conclusively if the problem is intermittent.)

Isn't troubleshooting fun? ;^)

But just to confirm: what I'm hearing is that frequencies can
mix and be reradiated by a turned-off radio, *but they need an
antenna* to get anywhere? ie, if the ELT is in the plane but
disconnected from the antenna, it's not likely the source of
the problem...likewise, if the portable nav/com is disconnected
from its antenna?

Have we likely absolved my plane at this point?


You mentioned the problem was considerably worse on *one* com than the other...
if the problem IS in the plane, that's my guess as to the source (see my other
post). Can you disconnect the antenna from *that* com, and fly with just the
other one?

Mark Mallory wrote in message ...

-If I drive to the antenna farm and get the interference,
-does it prove the problem is outside my plane, or just that
-the handheld is also more susceptible to it?

It could mean:
The antenna farm is clean; the handheld and your plane *both* have a problem.

Or, the handheld *is* the problem, since it's normally in the plane?
(but normally disconnected from its antenna)

The antenna farm has a problem; the handheld *may* be clean and
your plane *may* be clean.

Since you don't have enough information to distinguish between the above cases,
you can't rule your plane IN or OUT. On the other hand, if you HADN'T gotten
the interference on the ground with the handheld, you could probably rule the
plane IN (but still not conclusively if the problem is intermittent.)

Isn't troubleshooting fun? ;^)

Just Ducky (pun intended).

So what do you suggest to distinguish?

My ideas a
1) return to antenna farm w/ handheld and try to stay long enough
to get a station ID, also confirm lat long coordinates
if interference received:
2) fly w/out handheld in the plane
if interference received:
3) remove #2 nav com and ELT from plane
fly again
if no interference:
4) put one back

I called the FSDO last week and got the name of their frequency
guy, talked to him. If the problem reproduces today and I have
the street address and lat-long of the antenna, I'll call him back
with an update since "go right here and see what you find" is
an easier proposition than "there's a problem somewhere in this
vicinity"

I'm also thinking it might be worth a call to the TV station,
to see if they have someone who cares because maybe they have
better equipment and could check this out. (or maybe I can get
the FAA guy to call...)

You mentioned the problem was considerably worse on *one* com than the other...
if the problem IS in the plane, that's my guess as to the source (see my other
post). Can you disconnect the antenna from *that* com, and fly with just the
other one?

No problem, but it would be easier (as well as owner-allowed maintenance)
to just remove the radio -- if that would suffice? Or are you thinking
it's the antenna/cable?

IF it's the radio -- unfortunately it's a TKM. Are there bench
checks our local avionics guy should be able to run to see if it's
up to spec, before we ship it out to them?

Thanks!
Sydney

Channel two visual is 55.25 mHz and aural is 59.75 mHz. Their digital
channel is transmitted on channel 43 with a pilot frequency of 644.31
mHz. Digital audio and video are encoded into one data stream.
--
Gene Seibel
http://www.pad39a.com/gene/plane.html
http://www.pad39a.com/gene/broadcast.html




What is TV channel 2 digital sound frequency and normal
Channel 2 sound frequency? Just wondering if by chance
the difference between the two might be...127.0?? How
about Channel 2 and Channel 5?

Jim Weir wrote in message . ..
Well, then take other folks advice who have had this problem and solved it. I
gave you the method that works for me.

I take my hat off, then Jim. I could barely scrape up the
hour to drive around, much less weeks or days or even hours
to park patiently. We're going to have to get at this by
pragmatic combinations.

-If I drive to the antenna farm and get the interference,
-does it prove the problem is outside my plane, or just that
-the handheld is also more susceptible to it?

It proves that the problem is outside your aircraft.

But....does it? The handheld is normally *in* my aircraft.
Albeit, it is normally disassembled from the battery pack
and with the ducky antenna disconnected from it.

And..what about the testimony of the DE that she flies in
lotsa planes in that area all the time and never heard that
problem before?

why I suggested that you find a friend that lives close to the farm

No such critter alas. We live about as close to it as anyone we
know.

-How could my nav radios (or my handheld) be contributing
-to this problem when they are *powered off*?
good explanation snipped
If any of these
"spurious mixer products" falls within the passband of the nav input filter,
it will be reradiated out the nav antenna directly into your com antenna.
...
Did that help?

Yes, thank you! That was very clear.

But just to confirm: what I'm hearing is that frequencies can
mix and be reradiated by a turned-off radio, *but they need an
antenna* to get anywhere? ie, if the ELT is in the plane but
disconnected from the antenna, it's not likely the source of
the problem...likewise, if the portable nav/com is disconnected
from its antenna?

Have we likely absolved my plane at this point?

Sydney