Hi,

I'd like to use a camcorder in a light airplane, but I'd like the audio to
come from the aircraft intercom system (which carries both radio traffic and
crew conversations).

A typical light airplane has two jacks that you plug the headsets into. One
jack is I believe for the speaker part of the headset, and the other jack is
for the microphone.

So, I'm interested in interfacing from the "speaker" jack to a camcorder
"mic" or "aux" input.

The two things I'm concerned about a

a)Voltage differences in the signal.

b)Ground offset differences between the plane and the camcorder,
particularly if (later) I use a power adapter for the camcorder, which would
potentially link the ground reference of the plane with the ground reference
of the camcorder.

I would normally think just a voltage divider with a potentiometer would be
OK, but that doesn't cover the potential ground offset.

How do I findout what nominal voltage levels for airplane headsets and
camcorder inputs are?

Any other suggestions?

Thanks, Dave.

P.S.--Nobody seems to make such a product. I did find one product that went
inline with the microphone input of the headset, but that would only catch
one person talking. I'm interested in recording everything that comes to
the headsets, including radio traffic.

On Thu, 26 Oct 2006 16:30:51 -0400, "David T. Ashley"
wrote:

Hi,

I'd like to use a camcorder in a light airplane, but I'd like the audio to
come from the aircraft intercom system (which carries both radio traffic and
crew conversations).

A typical light airplane has two jacks that you plug the headsets into. One
jack is I believe for the speaker part of the headset, and the other jack is
for the microphone.

So, I'm interested in interfacing from the "speaker" jack to a camcorder
"mic" or "aux" input.

The two things I'm concerned about a

a)Voltage differences in the signal.

b)Ground offset differences between the plane and the camcorder,
particularly if (later) I use a power adapter for the camcorder, which would
potentially link the ground reference of the plane with the ground reference
of the camcorder.

I would normally think just a voltage divider with a potentiometer would be
OK, but that doesn't cover the potential ground offset.

How do I findout what nominal voltage levels for airplane headsets and
camcorder inputs are?

Any other suggestions?

Thanks, Dave.

P.S.--Nobody seems to make such a product. I did find one product that went
inline with the microphone input of the headset, but that would only catch
one person talking. I'm interested in recording everything that comes to
the headsets, including radio traffic.



1. I'm sure there are products to do this. I'll check for you.
Recording the audio is not uncommon.

2. You can isolate the grounds with either capacitors, or an audio
transformer. The transformer idea might be useful as it can help with
the issue of impedence mis-match.

3. Leve shoudl be close if you use the cam-corder's line in jack. If
you use the mic jack, I"m sure the level will be too high. Then a
potentionometer or a fixed divider will work, IMHO.

I don't see any ground offset issues myself, I think you will find the
headphone jack is referenced to ground, as is the camcorder's line in
jack. Both are easy to check with a small meter.

Before connecting *anything* to the aircraft be sure you understand
the implications of what you are doing. If you 'break' the
communications system at teh wrong time, the result could be
ugly--someone could be killed. Make sure there is an approved isolator
panel in teh aircraft that you tie into--these serve to prevent
anythign on one circuit from interfering with the other circuit(s).

"PeterD" wrote in message
...
1. I'm sure there are products to do this. I'll check for you.
Recording the audio is not uncommon.

After I made the post, I did find the PA-80S he

http://www.pilot-usa.com/adaptercables.htm

Seems to be the right thing. The company has advised me it goes to the LINE
jack.

2. You can isolate the grounds with either capacitors, or an audio
transformer. The transformer idea might be useful as it can help with
the issue of impedence mis-match.

The audio transformer seems like the right idea. It provides total
isolation, whereas the cap approach requires that one wire be connected
directly between the jack and the camcorder.

3. Leve shoudl be close if you use the cam-corder's line in jack. If
you use the mic jack, I"m sure the level will be too high. Then a
potentionometer or a fixed divider will work, IMHO.

I don't see any ground offset issues myself, I think you will find the
headphone jack is referenced to ground, as is the camcorder's line in
jack. Both are easy to check with a small meter.

Before connecting *anything* to the aircraft be sure you understand
the implications of what you are doing. If you 'break' the
communications system at teh wrong time, the result could be
ugly--someone could be killed. Make sure there is an approved isolator
panel in teh aircraft that you tie into--these serve to prevent
anythign on one circuit from interfering with the other circuit(s).

In practice, I'm going to use the proven solution from the company cited
above (or, if you find other products, one that you suggest). This should
minimize the risk of home-brew circuits.

Thanks for your help, Dave.

On Thu, 26 Oct 2006 19:10:49 -0400, "David T. Ashley"
wrote:

"PeterD" wrote in message
.. .
1. I'm sure there are products to do this. I'll check for you.
Recording the audio is not uncommon.

After I made the post, I did find the PA-80S he

http://www.pilot-usa.com/adaptercables.htm

Seems to be the right thing. The company has advised me it goes to the LINE
jack.

2. You can isolate the grounds with either capacitors, or an audio
transformer. The transformer idea might be useful as it can help with
the issue of impedence mis-match.

The audio transformer seems like the right idea. It provides total
isolation, whereas the cap approach requires that one wire be connected
directly between the jack and the camcorder.

3. Leve shoudl be close if you use the cam-corder's line in jack. If
you use the mic jack, I"m sure the level will be too high. Then a
potentionometer or a fixed divider will work, IMHO.

I don't see any ground offset issues myself, I think you will find the
headphone jack is referenced to ground, as is the camcorder's line in
jack. Both are easy to check with a small meter.

Before connecting *anything* to the aircraft be sure you understand
the implications of what you are doing. If you 'break' the
communications system at teh wrong time, the result could be
ugly--someone could be killed. Make sure there is an approved isolator
panel in teh aircraft that you tie into--these serve to prevent
anythign on one circuit from interfering with the other circuit(s).

In practice, I'm going to use the proven solution from the company cited
above (or, if you find other products, one that you suggest). This should
minimize the risk of home-brew circuits.

Thanks for your help, Dave.



I think you've made the best choice! Good luck with it.