On Sun, 6 Jul 2003 16:32:41 +0000 (UTC), Jim Pennino
wrote:

In rec.aviation.owning Jim Weir wrote:
"Paul"
shared these priceless pearls of wisdom:

-
-"Jim Weir" wrote in message
.. .
- I don't know. I've never used a handheld. I've got a Kenwood 231 mounted
-like
- an airplane radio in the stack and plumbed through the audio panel to the
- headsets.
-
-
-Are the mike inputs and audio outputs compatible with the aviation headset
-impedance?

Not really. The standard aircraft mic simulates an old carbon element. You get
roughly half a volt to a volt p-p across something like 300 ohms. A standard
dynamic input to a ham rig is a few millivolts across a couple of dozen ohms. A
standard electret input is a couple of tenths of a volt across 2K or so.

The standard aircraft earphone wants a volt or two p-p across 150 ohms. The
normal ham rig output is speaker level (a couple of volts into 8 ohms).

The point is, there IS no ham radio standard, while the aircraft headset
standard is quite well defined. You can't just hook the aircraft headset into
the ham rig on a PNP basis. You always wind up dicking around with voltage and
impedance shifters to make it play well.

Jim

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

FWIW, the July QST Hints & Kinks column had this discussion with a simple
circuit to use an aviation headset with a ham rig.

It's far, far simpeler to just get one of the little ear pieces with
the small lapel mike. Probably cheaper in the long run ...

They are inexpensive so why bother messing around with a good head set
when you don't have to.

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