Caps are short for "Capacitors". I have been looking for where I
reverse engineered and drew the schematic for the Head Sets inc power
supply but I have not been able to find it. I may have tossed it so I
will have to go from memory of about two years ago when I fixed mine.
It is installed in the aircraft so I can not look at it. I think
that they use two LM340 three terminal regulators and a TI low cost DC
to DC converter. You can down load the data sheets at:
http://www.national.com/pf/LM/LM340.html#Datasheet

Add the capacitors recommended by the data sheet and parallel with a
0.1uf ceramic cap for RF bypassing. Get someone that knows how to
solder electronics to do this for you.

Maybe Head sets Inc has gotten wise and fixed the design but they were
still clueless at Oshkosh.

John

On Sun, 19 Oct 2003 18:54:05 -0500, "B. Jensen"
wrote:

John,

Thanks for the reply. I'm not a very astute electrical guy, so please
explain to me what "caps" are and how I can modify the power cord to my
Headsets Inc. ANR to eliminate this problem.

Many thanks,

BJ

wrote:

There is a very good chance that the RF from your transmitter is
getting into the Head Sets Inc power supply since they lack the
necessary bypass caps on the input and output and is causing the
squeal that you hear.

The power supply they sell leaves a lot to be desired. They did not
install any bypass caps on the internal three terminal regulators and
they tend to oscillate due to the aircraft wiring inductance and lack
of sufficient loop margin. The caps are shown on the regulator data
sheets and are needed to insure sufficient loop gain and phase margin.
The internal DC to DC switching converter also puts out loads of
unstable harmonics that is easily visible on a spectrum analyzer. If
you look at the wave forms on a scope you will see several cycles of
ringing each time the converter switches. This indicates very poor
gain & phase margin on the three terminal regulators. I added 4
small caps and now it no longer spoils reception of my Loran and ADF.


Whoever designed the Head Sets Inc power supply needs to be sent back
to Electronics 001 class.

John

On Fri, 17 Oct 2003 02:52:30 -0500, "B. Jensen"
wrote:



I just hard wired my ANR headset into my ship's power so that I no
longer have to use a 9v battery as a power source. Now I am getting an
intermittent squeal when I transmit. I never had this problem with the
9v power pack. My ANR is a Headsets Inc. conversion to a David Clark
headset.

Any ideas how to solve this problem. I used the Headset's Inc. power
cord for the installation.

Thanks,

BJ