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1992-05-13
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113 lines
---WIRING AN EXTERNAL SPEAKER-MIKE FOR AN ICOM 24AT H/T---
---Written by Noah Lehmann-Haupt KB2NDR---
---May 13, 1992---
DISCLAIMER
I am writing this document for the use of the general Amateur
Radio community. It is being done in order to try to assist amateurs
in making their radio system work. I hereby do NOT GUARANTEE IN ANY
WAY that the following procedure will DEFINITELY work for your radio.
If for some reason it does not, I hold NO RESPONSIBILITY for any im-
proper actions taken on your part or on mine.
* * *
This was written for use with an Icom 24-AT, but should work with all
"like" radios (NOT the W2A). However, it has not been tested on any-
thing but the 24AT.
* * *
INTRODUCTION
Recently, I have noticed a great deal of people who are start-
ing to get into their own "homebrewing" of equipment. I, for one, am
always looking for the cheap way out (if you can call owning a TS-440S
and an Icom 24-AT cheap.) A couple of months ago, I had some spending
cash available, and since the the big thing I wanted was a Yagi and a
tower, and that was TOO big, I decided to get something that I could
really use in the Shack, which was an external mic for my HF rig, and
possibly for my H/T. Flipping through the AES catalog, I noticed the
Heil BM-10 Boomset. That seemed pretty nice; it had stereo headphones,
a very nice Heil mic, with the HC-4 element installed, and was basically
just what I was looking for...except the $85 price tag. After a long
fight with my willpower, I being the victor, I decided it would be a nice
addition to the hamshack. The only thing was that it came wired only
Icom, Yaesu, and Kenwood HF rigs, and NOT for any type of H/T. Thinking
that I could figure some way to wire it to my IC-24AT, I said "why not?"
and bought the thing, with the high-freq. response HC-4 DX'ing mic element
installed. I also got the separate, lower freq. "Rag Chewing" HC-5 Mic
element. When I got the whole setup in the mail, The first thing I did was
to put together a make-shift PTT switch, by hooking up a regular push button
switch to a 1/4" Phono Plug with a long wire (this plugged into the "Foot-
switch" jack on the mic.) This would mean I could use the mic without
VOX for those time I had a cough, or something noisy like that. The mic
, by the way, was pre-wired for my Kenwood HF rig, with an 8-pin female
plug on the end. Let me get to the point, so after some feeble attempts
to wire the thing to my H/T, I finally got it.
PARTS
The following parts are needed for the wiring to work correctly:
1. A 2.5 mm Sub-mini 2-conductor audio plug (Radio Shack (RS) 274-279)
2. A 33K Ohm resistor (RS-271-040)
3. A .47 uF Tantalum Capicitor (RS-272-1433)
4. A MALE 8-pin Radio Plug (optional--for mics wired for Kenwood HF rigs
Any MALE plug, depending on you rig, may be used, but is not essential)
5. 3-conductor (or 4) shielded wire (optional--RS-278-777)
6. A Soldering Iron
7. X-Acto or similar knife
PROCEDURE
In this procedure, we are assuming you are connecting a mic wired
for a Kenwood HF rig--modify the instructions accordingly.
First, note the color, or just note, which wire is which: Mic, Shield,
and PTT. Solder the mic wire to pin 1 on your male plug, or connect the mic
wire to the mic output of your microphone. Next, connect the PTT center to
pin 2 of the MALE 8-pin plug, etc. Connect the PTT ground (if any) to pin 8
of the 8-pin plug. The mic shield goes to pin 7. After this has been completed,
connect all grounds to the Shield of the phono plug. Then connect BOTH the
PTT center and the mic center to the tip of the phono plug. The next step
can be modified in any way, but generally, you now want to cut the PTT and mic
center wires below the phono connector and install a 33k resistor in series
with the PTT center line (make sure you know which wire that is) and install
the .47 uF cap. in series with the mic center line, making sure the + end is
toward the plug. Wrap the entire connection with electrical tape or some sort
of insulating connection, making sure not to short either of the lines to
ground accidently. Again, this procedure should work with any mic, not
necessisarily a Heil mic, and not necessisarily a Kenwood rig. The only things
specific to the Kenwood rig are the pin connections on the 8-pin plug. The
resistor and capacitor are universal.
** NOTE **
In a recent QST, Icom's Tech Talk column/ad gave the above procedure, but
they said to connect the mic and PTT to the center ring on a STEREO plug.
That may work, but the above setup has been tested and SHOULD WORK on a
24AT radio. If you have any problems feel free to contact me anytime:
Noah Lehmann-Haupt KB2NDR
627 west 247th street
Bronx, NY 10471
USA
I have included a .GIF file in this ZIP file containing a ROUGH (hihi)
sketch of what the setup should look like. Remember, it was drawn by hand.