[Boatanchors] Aviation Headset

[Sheldon Daitch]

I had a David Clark H10-40 with the Electret microphone and as best as I remember, I could use it with my Icom IC-02AT with nothing more than an adapter cable for the headphone side.  

The microphone was a little more complex than just cable adapters, as the IC-02AT uses voltage switching on the microphone tip to ground for XMIT.

The Icom uses T-S mike plug while the headset has a T-R-S plug.

My mike adapter cable has the T-R-S jack for the headset and a 28K ohm resistor between T and R.  Shorting the T to S would bring the Icom into transmit mode.

73
Sheldon


________________________________________
From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> on behalf of Richard Knoppow <1oldlens1 at ix.netcom.com>
Sent: Friday, December 27, 2013 8:15 AM
To: dhallam at knology.net; Boatanchors-qth
Subject: Re: [Boatanchors] Aviation Headset

----- Original Message -----
From: "David C. Hallam" <dhallam at knology.net>
To: "Boatanchors-qth" <boatanchors at mailman.qth.net>
Sent: Thursday, December 26, 2013 8:23 AM
Subject: [Boatanchors] Aviation Headset


>I have an Aviall microphone/earphone headset and can't seem
>to find any information about the microphone or earphone
>impedance.  It seem that the company is now owned by Boeing
>and don't sell this type of item anymore.  Is there some
>kind of standard impedance for aviation headsets?  I also
>don't seem to see any model number on the headset either.
>Does anyone know where I can find the information?
>
> David
> KW4DH

    Aviall appears to be a marketing organization run by
Boeing Aircraft.  Its likely the phones are made by someone
else and marketed by Aviall under their own name.  I checked
David Clark Company for the specs on their military aviation
headphone sets.  The phones are very low impedance, about 30
ohms each and the microphones are moving coil dynamic types
with an impedance of around 5 ohms.  I don't know if this is
a defactor standard.  Very old head sets with microphones
may have higher impedance, on the order of 300 ohms per
phone and possibly carbon microphones. Typical carbon
microphones have a resistance on the order of 25 to 50 ohms
and usually work with about 4 volts across the mic. The old
standard AT&T telephone microphones worked at 4.5 volts. If
your phones have a very low Z dynamic mic and must work into
a HI-Z input a speaker output transformer may work. Usually
commercial dynamic microphones had voice coil impedances of
anywhere from 8 to 30 ohms and built-in transformers for
matching higher Z.  Some had 150 ohm voice coils for direct
use with medium-impedance broadcast type amplifiers. (I
think some EV mics have direct voice coils like this).  The
headphones will work off any loudspeaker amplfier but the
mic may require some if its really low-Z since its output
voltage will be very low.
    A lot of aviation type headsets have various
noise-cancelling arrangements both for microphone and
headphone.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com

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