where exactly to put the noise filter

[Dico Reyers]

Hi There,

We have a 1966 mooney m20e.

We're just in the process of putting in a noise filter so that it will
hopefully reduce some of the static on the radio.

I'm wondering if the filter goes between the generator and the voltage
regulator.... or if the filter goes between the voltage regulator and
the buss.

Any help would be appreciated,

Thanks...

-Dico

[mikem]

Dico,

What problem are you trying to cure?

If you have "popping" type of static in your Com/Nav receiver, then you
have a bad shield on a spark plug, or poor shielding on your P-leads
where they run from the mag to the mag switch. Noise filter on the
alternator wont do anything for this...

If you have audible strobe squeal which goes away if you turn off the
strobes, ditto... This requires work in the audio wiring and possibly in
the strobe cabling .

If you have alternator howl or whine which varies with engine speed, and
goes away if you turn off the ALT field, then a noise filter installed
on the alternator is unlikely to do much, either... This means that
your audio wiring (audio panel, intercom, mic/headphone jacks) need
attention.

If you have "hash" type noise on the Com/Nav receiver, then see if it
goes away when the engine is stopped (on the ground). If it does, then
it is likely induced by mechanical vibration. Bad antennas, bad coax
fittings, radios not properly seated in the rack can cause this.

About the only symptom which installing a filter on the alternator is
likely to cure is if you have "hash" type noise when listening to
200-400Khz on your ADF receiver.

MikeM
Skylane '1MM
Pacer '00Z




Dico Reyers wrote:

> Hi There,
>
> We have a 1966 mooney m20e.
>
> We're just in the process of putting in a noise filter so that it will
> hopefully reduce some of the static on the radio.
>
> I'm wondering if the filter goes between the generator and the voltage
> regulator.... or if the filter goes between the voltage regulator and
> the buss.
>
> Any help would be appreciated,
>
> Thanks...
>
> -Dico

[Jay Honeck]

Hey Mike,

What's the cure for "bleed through" from one com radio to the other?

We usually keep "Com 2" tuned to our local AWOS frequency. When we're near
Iowa City, we can faintly hear it in the background through our
headphones -- even when "Com 2" or "Both" aren't selected on our audio
panel.

Of course, this isn't an issue without ANR headsets (couldn't hear it), or
when we're far enough away from the strong signal -- but it's one of those
little annoyances that always bugs us.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[mikem]

Jay Honeck wrote:

> Hey Mike,
>
> What's the cure for "bleed through" from one com radio to the other?

Usually "bleed through" refers to the effects of RF overload on Com2
while transmitting on Com1, or vice versa. Most audio panels contain
automatic muting circuits which completely block the audio from opposite
com reciever while the other's transmitter is keyed.

> We usually keep "Com 2" tuned to our local AWOS frequency. When we're near
> Iowa City, we can faintly hear it in the background through our
> headphones -- even when "Com 2" or "Both" aren't selected on our audio
> panel.

This sounds like inadequate isolation in the audio source switching of
the audio panel. Most of modern audio panels (King, PSE, RST) do not
intrisically have this problem. I think you have a PSE, which shouldn't
do this.

It is likely that your installer did something funky with the audio
wiring between Com1/Com2 and the audio panel to induce this. Could be
that the Speaker outputs of the Com radios are wired to 8 Ohm dummy load
resistors inside the audio panel. If the installer took a shortcut and
shared the ground connection from speaker-low output on the Com(s) to
the audio ground on the audio panel, it created a classic ground loop
between the speaker audio loop and the headphone output loop, thereby
creating the crosstalk. Better wiring technique might have prevented this.

Most modern Com radios dont care if the speaker outputs are terminated
into a dummy load resistor when not connected to the overhead speaker,
so it isn't even necessary to utilize those loads built into the audio
panel.

> Of course, this isn't an issue without ANR headsets (couldn't hear it), or
> when we're far enough away from the strong signal -- but it's one of those
> little annoyances that always bugs us.

For further diagnosis, I'll bet that if you turn the volume control of
the non-selected comm radio down, then the bleedthrough will go away.
Also try switching the non-selected com receiver to the overhead speaker
while listening to the primary com on the ANR headsets, and report back.

MikeM
Skylane \1MM
Pacer \00Z

[Nathan Young]

On Fri, 20 Feb 2004 17:57:10 GMT, "Jay Honeck"
> wrote:

>Hey Mike,
>
>What's the cure for "bleed through" from one com radio to the other?
>
>We usually keep "Com 2" tuned to our local AWOS frequency. When we're near
>Iowa City, we can faintly hear it in the background through our
>headphones -- even when "Com 2" or "Both" aren't selected on our audio
>panel.
>
>Of course, this isn't an issue without ANR headsets (couldn't hear it), or
>when we're far enough away from the strong signal -- but it's one of those
>little annoyances that always bugs us.

Jay - what make/model are the COM radios in your plane?

-nathan

[Jay Honeck]

> This sounds like inadequate isolation in the audio source switching of
> the audio panel. Most of modern audio panels (King, PSE, RST) do not
> intrisically have this problem. I think you have a PSE, which shouldn't
> do this.

Actually, I have a Narco CP-136 audio panel.

(See a picture of this model at http://www.ronhahn.com/Hawk-XP/CP136.html )

> For further diagnosis, I'll bet that if you turn the volume control of
> the non-selected comm radio down, then the bleedthrough will go away.

Yep, I believe it does. So this means the audio panel is wired incorrectly?

> Also try switching the non-selected com receiver to the overhead speaker
> while listening to the primary com on the ANR headsets, and report back.

Okay, will do. I should expect to hear the AWOS broadcasting quietly on the
speaker, I presume, same as I hear in my headset?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jay Honeck]

> Jay - what make/model are the COM radios in your plane?

Com 1 is a brand new Narco 810-R, digital. (It's the slide-in replacement
for the Com 120)

Com 2 is an old-but-perfect Narco 120.

Both work flawlessly.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Nathan Young]

On Fri, 20 Feb 2004 23:11:27 GMT, "Jay Honeck"
> wrote:

>> Jay - what make/model are the COM radios in your plane?
>
>Com 1 is a brand new Narco 810-R, digital. (It's the slide-in replacement
>for the Com 120)
>
>Com 2 is an old-but-perfect Narco 120.

Hi Jay,

Take this with a caveat as I am a digital engineer who likes to learn
about RF stuff. I could be in left field here...

I asked because I was trying to determine if the radios utilized the
same IF frequency (which they would if it is the same radio). I don't
know enough about the Narco 810 or 120 to determine if they share the
same IF.

Where I was going with this...

The bleedthrough might be leakage from the IF section of one radio
coupling into the IF of the other radio. That would explain why the
audio is only noticeable as you are near the AWOS transmitter, where
the energy entering the IF stage on COM2 would be strongest.

An interesting test would be:

1. Shut off COM2 on the audio panel
2. Fly to a distant location where you can't hear the bleedthrough.
3. Turn on the audio for COM2
4. Can you hear the AWOS over the audio panel?

If you can hear the audio, then I suspect the audio problem is related
to the radio and not the audio panel (or audio wiring).

-Nathan

[MikeM]

Jay Honeck wrote:

>>This sounds like inadequate isolation in the audio source switching of
>>the audio panel. Most of modern audio panels (King, PSE, RST) do not
>>intrisically have this problem. I think you have a PSE, which shouldn't
>>do this.
>
>
> Actually, I have a Narco CP-136 audio panel.

I do not have any experience with these, so the lack of isolation could be
a shortcoming of the design.
>
> (See a picture of this model at http://www.ronhahn.com/Hawk-XP/CP136.html )
>
>
>>For further diagnosis, I'll bet that if you turn the volume control of
>>the non-selected comm radio down, then the bleedthrough will go away.
>
>
> Yep, I believe it does. So this means the audio panel is wired incorrectly?

It just means that the bleed-through is happening at audio frequencies; not by
one IF coupling to the other IF as another poster postulated.


>>Also try switching the non-selected com receiver to the overhead speaker
>>while listening to the primary com on the ANR headsets, and report back.
>
>
> Okay, will do. I should expect to hear the AWOS broadcasting quietly on the
> speaker, I presume, same as I hear in my headset?

Yes, but try to determine if the faint feedthrough you hear in your headphones
is reduced by routing com2 to the speaker. It will be a subtle difference,
because the speaker audio will leak into your headphones accoustically. If the
feedthrough is reduced, then my speculation about the dummy load resistors would
warrant more investigation.

MikeM
Skylane '1MM
Pacer '00Z

[Jay Honeck]

> An interesting test would be:
>
> 1. Shut off COM2 on the audio panel
> 2. Fly to a distant location where you can't hear the bleedthrough.
> 3. Turn on the audio for COM2
> 4. Can you hear the AWOS over the audio panel?
>
> If you can hear the audio, then I suspect the audio problem is related
> to the radio and not the audio panel (or audio wiring).

I don't think I've got enough information here. What position would I have
the audio panel in for this test? Com 1, Com 2, or Both?

And, assuming Both, what do you mean when you say "Can I hear the AWOS over
the audio panel?" Do you mean on the speaker? Or in my headphones?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Nathan Young]

On Sat, 21 Feb 2004 02:24:12 GMT, "Jay Honeck"
> wrote:

>> An interesting test would be:
>>
>> 1. Shut off COM2 on the audio panel
>> 2. Fly to a distant location where you can't hear the bleedthrough.
>> 3. Turn on the audio for COM2
>> 4. Can you hear the AWOS over the audio panel?
>>
>> If you can hear the audio, then I suspect the audio problem is related
>> to the radio and not the audio panel (or audio wiring).
>
>I don't think I've got enough information here. What position would I have
>the audio panel in for this test? Com 1, Com 2, or Both?
>
>And, assuming Both, what do you mean when you say "Can I hear the AWOS over
>the audio panel?" Do you mean on the speaker? Or in my headphones?

Ahhh, not exactly clear given your audio panel. I was debugging this
thinking of the KMA24 in my plane. I meant headphones only.

Going back a few steps (to make sure we're debugging the correct
problem) - the initial problem was with ONLY COM1 selected, you hear
the station that COM2 is tuned (to) through the headset?

For step 1 above, listen ONLY to COM1, but leave COM2 on and tuned to
the AWOS. You should still hear the AWOS on the bleedthrough on COM1.

Once you get far enough away that you no longer hear the bleedthrough,
deselect COM1 and select COM2 to be played through the headset. See
if you can hear the AWOS.

If you can hear the AWOS, I suspect the problem is due to IF coupling
between the radios. The reasoning being that if COM2 is still
receving the AWOS and producing audio - but the bleedthrough is gone,
than it is not a wiring/audio panel problem.

Anyway, Mike's idea is a bit easier to check. Vary the volume on COM2
and see if the volume on the bleedthrough changes. If it does, you
probably have some combination of a wiring/audio panel problem.

If it doesn't try my test.

Aren't avionics in 30 year old planes fun?

-Nathan

[Jay Honeck]

> Going back a few steps (to make sure we're debugging the correct
> problem) - the initial problem was with ONLY COM1 selected, you hear
> the station that COM2 is tuned (to) through the headset?

Yes, very faintly. It's only noticeable on (or over) the field, with the
AWOS transmitter nearby.

> Once you get far enough away that you no longer hear the bleedthrough,
> deselect COM1 and select COM2 to be played through the headset. See
> if you can hear the AWOS.

I already know the answer is "yes." The bleedthrough is only audible when
we're close to the transmitter.

> If you can hear the AWOS, I suspect the problem is due to IF coupling
> between the radios. The reasoning being that if COM2 is still
> receving the AWOS and producing audio - but the bleedthrough is gone,
> than it is not a wiring/audio panel problem.

Okay, so what would the "fix" be?

Thanks!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jim Weir]

A. We know that this cannot be the problem (IF coupling) because Jay tells us
that if he turns the volume down to near zero on the AWOS radio that the
bleedover goes away. The volume control is WAY downstream of the last IF stage,
and has no control over the amplitude of the IF signal.

B. In forty years in this business, I've never had an aircraft radio (even when
two identical radios are in a stack on top of one another) bleed IF from one
into the other. Never. Not even through a ****poor receive antenna coupler
with lousy isolation.

C. The odds are that the headphone outputs of the two radios (which is what we
all use to drive both phones and speaker of an audio panel) are closecoupled so
that there is capacitive coupling from one headphone lead to the other. One
thing that Narco may or may not have done is to terminate the headphone leads
inside the audio panel with a resistive load (150-600 ohm resistor). If they
did NOT do that on this particular model, the capacitive crosscoupling between
the headphone inputs will be magnified.

It remains for somebody in this ng with access to the chassis schematic of Jay's
audio panel to see if Narco did in fact terminate the headphone inputs. If they
did, then a simple wrap of one headphone lead or the other with tinfoil will
tell us if it is wire to wire coupling, and then the fix is a simple replacement
of one of the headphone wires with shielded cable.

Jim



"Jay Honeck" >
shared these priceless pearls of wisdom:

->
->> If you can hear the AWOS, I suspect the problem is due to IF coupling
->> between the radios. The reasoning being that if COM2 is still
->> receving the AWOS and producing audio - but the bleedthrough is gone,
->> than it is not a wiring/audio panel problem.
->
->Okay, so what would the "fix" be?

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

[Ray Andraka]

It may be a shortcoming with the CP136 design too. If the volume of the
non-selected radio is up on mine, you can hear it. Same with the VORs. Was true
both before and after I pulled one of the MX11s and a Nav11 and replaced them with a
KX155. Turning down the volume on the offending unit fixes it, so it is definitely
something with the audo circuit. Since any radio including the VORs, marker beacon
and ADF do it, I assume it is the CP136M that is providing the bleedthrough path.

Jim Weir--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

[Jay Honeck]

> Since any radio including the VORs, marker beacon
> and ADF do it, I assume it is the CP136M that is providing the
bleedthrough path.

Nuts. And to think I just worked three days to repair this audio panel!

Is there a solution that my avionics shop can do, or is it just something to
live with? It's not a real hardship -- heck, I can't even detect it with
my ANR turned off -- but it is one of those minor annoyances that grates on
me every time we fly.

Thanks Ray, Jim, Nathan, Mike and everyone...
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Don Tuite]

On Sat, 21 Feb 2004 20:49:18 GMT, "Jay Honeck"
> wrote:

>Is there a solution that my avionics shop can do, or is it just something to
>live with?

Put on your headphones at home and listen to the 1812 at high volume
about 20 times. Or spend a day at a pistol range.

Nature is always the best remedy.

Eh?
Don

[Jay Honeck]

> Put on your headphones at home and listen to the 1812 at high volume
> about 20 times. Or spend a day at a pistol range.

Heh.

Along those same lines, I've slowly fixed everything that was wrong with The
Mighty Grape (our fuel truck) when we bought it. For just $1800, you expect
a LOT of cosmetic problems, and, one by one, I've fixed them all.

The last thing wrong is that the "Check Engine" light is on, all the time.
There's nothing wrong with the engine, according to my mechanic, but the
Nissan dealer wants $70 to hook it up to his machine, and turn off the
damned light.

A piece of black electrician's tape did the job perfectly -- just like your
pistol range...

;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Drew Dalgleish]

On Sat, 21 Feb 2004 21:57:45 GMT, "Jay Honeck"
> wrote:

>> Put on your headphones at home and listen to the 1812 at high volume
>> about 20 times. Or spend a day at a pistol range.
>
>Heh.
>
>Along those same lines, I've slowly fixed everything that was wrong with The
>Mighty Grape (our fuel truck) when we bought it. For just $1800, you expect
>a LOT of cosmetic problems, and, one by one, I've fixed them all.
>
>The last thing wrong is that the "Check Engine" light is on, all the time.
>There's nothing wrong with the engine, according to my mechanic, but the
>Nissan dealer wants $70 to hook it up to his machine, and turn off the
>damned light.
>
>A piece of black electrician's tape did the job perfectly -- just like your
>pistol range...
>
>;-)
>--
>Jay Honeck
>Iowa City, IA
>Pathfinder N56993
>www.AlexisParkInn.com
>"Your Aviation Destination"
>
>
sometimes you can get rid of those lights by disconnecting the battery
for a few min.

[Jay Honeck]

> sometimes you can get rid of those lights by disconnecting the battery
> for a few min.

And lose all my radio stations? :-)

I'll try it -- thanks!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[john smith]

Jay Honeck wrote:
>>sometimes you can get rid of those lights by disconnecting the battery
>>for a few min.

> And lose all my radio stations? :-)

Plug a 9V battery into the cigarette lighter plug.

[Greg Burkhart]

"Jay Honeck" > wrote in message
news:gv2_b.367138$I06.3828612@attbi_s01...
> > sometimes you can get rid of those lights by disconnecting the battery
> > for a few min.
>
> And lose all my radio stations? :-)

Both of them???
;-)

[Aaron Coolidge]

Jay Honeck > wrote:
:> Jay - what make/model are the COM radios in your plane?

: Com 1 is a brand new Narco 810-R, digital. (It's the slide-in replacement
: for the Com 120)

: Com 2 is an old-but-perfect Narco 120.

Jay, just for you I tried out a little test this morning on my flight to
Martha's Vineyard. I borrored a friend's Arrow, which has
Narco CP-136 audio panel
Narko Mk12D nav/com + IDxxx (Integrated DME)
Garmin 300XL gps/com

As I arrived in the pattern, I had the ATIS on com2 and tower on com1.
I had the "COM1" button pushed in. I pushed in the "BOTH" button and
verified that I could hear the atis. I shut off the "BOTH" and I
could not hear the atis on top of the tower freq.

When I left I switched radios (ATIS on com1, tower on COM2), with the
same results: the radio switched out on the audio panel can't be heard.

I'm not sure what this means to you - you DID want a new audio panel,
didn't you?
--
Aaron Coolidge (N9376J)

[Jay Honeck]

> I'm not sure what this means to you - you DID want a new audio panel,
> didn't you?

No! It works and looks perfect now, after much work.

Interesting that you're not hearing the cross-talk. I suppose this must
mean Jim's (and/or Mike's) theory is correct? Something is wired
incorrectly?

Thanks for taking the time to check this out.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jim Weir]

I didn't say it was WIRED incorrectly. It was either DESIGNED incorrectly or
INSTALLED incorrectly or FAILED INTERNALLY or NOT JUMPERED CORRECTLY.

Jim


"Jay Honeck" >
shared these priceless pearls of wisdom:


->Interesting that you're not hearing the cross-talk. I suppose this must
->mean Jim's (and/or Mike's) theory is correct? Something is wired
->incorrectly?



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

[Jay Honeck]

> I didn't say it was WIRED incorrectly. It was either DESIGNED incorrectly
or
> INSTALLED incorrectly or FAILED INTERNALLY or NOT JUMPERED CORRECTLY.

Well, I think we can rule out the "bad design" theory, since another
poster's CP-136 doesn't exhibit the same "cross-talk" symptom...

So I guess that leaves the last three possibilities? I'm rooting for the
"not jumpered correctly" theory, myself. Either way, next time it's in the
avionics shop, I'll tell the guys the various theories and possible fixes.

I always like it when the avionics techs roll their eyes that way... ;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Bushy]

> > And lose all my radio stations? :-)
>
> Both of them???
> ;-)


Country AND western?

Such diverse taste!

;<)
Peter