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From: rvanzant@oreally.sevenex.sol.net (Robert Van Zant)
Newsgroups: rec.radio.amateur.digital.misc
Subject: Re: htx-202 9600 mod?
Date: 24 Jan 1995 15:07:45 -0600
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: : Is there a source for a 9600 baud mode for the Radio Shack htx-202 2m
: : handheld?

: There probably is but I hope you're good at micro-surgery HI.

     I wouldn't exactly call it micro-surgery.  It's a wee bit tight, but a
steady hand and a magnifying lense was all I needed (and a soldering iron).
Actually bringing the leads out of the case is the tough part, as it's
pretty tight in there.  Here's the how-to I've had lying around for some
time.  Obviously, I'm not the author, so credit where credit is due.

========================================================================
From: Gene Kennedy <Gene.Kennedy@f470.n3625.z1.fidonet.org>
Date: Wed, 30 Nov 94 06:04:00 -0600
Subject: 9600 Baud
Organization: Di's Online Cafe - Mobile, AL - (205) 661-8945

To Steve and others who may be interested, heres how I connected my 9600
baud TNC to my HTX-202:

CONNECTIONS TO REALISTIC HTX-202 FOR 9600 BAUD PACKET

NOTE:  The following operation requires soldering in very close quarters
and damage or destruction of your radio is possible if you get too much
heat on nearby wires or components, or by sloppy soldering.

     I performed these operations on my own HTX-202 and it works OK for
9600 baud operation with my new Kantronics KPC-9612.  I don't take any
responsibility for invalidation of warranty or improper operation of the
radio, etc.

     I studied the schematics and determined the locations for making
connections based on general recommendations for 9600 FSK.  I didn't
want to permanently deface my radio by making any holes in the case for
wire penetrations, so I removed the battery and battery connector which
is a plastic oval with a spring contact in it held by two screws and ran
the wires out to the connector that goes to the TNC.  I can restore it
to original condition in just a few minutes. I used the smallest coax I
had avail, I think it is RG-174.  Someone may have a better idea about
doing that part.

Open up the HTX-202 by removing the five screws, take off back cover,
and separate front panel and lay it on bench so that flex pc cable won't
be damaged.

 Knobs   ______________________________________
  \  __ |                                      |
    |   |      HF      /here ------------      |
     -- |     --------'--    -------,----      |
     __ |                  MIC      0\here     |
    |__ |                          RV1         | <hole in
     __ |                        ------        |  bottom
    |__ |                       |_vco__|       |
        |   Top of main PCB                    |
        |______________________________________|

   This is a crude diagram of the inside of HTX-202 after splitting
case and folding front case aside.  There are several sub-PCBs
standing on edge that I represented by the dashed lines.  In my HTX-202
the sub-board at upper left is labeled HF and the raw output from the
discriminator IC goes into pin 1, the first solder pad starting from
the center of the radio.  This is where I soldered a small coax and ran
it out the hole in bottom of case.  This is Receive Audio into TNC.

   The sub-board labeled MIC is microphone audio to modulator varicap.
Pin 6 here goes directly into the VCO and this is where I soldered a
second coax.  The solder pad 6th pin from center of radio is right next
to the RV1 deviation pot.  (Dont melt the pot.)  This is Transmit Audio
from TNC.

   The third connection, PTT, is harder to describe the actual point.
What I did was flip the radio over and used a ohm meter to locate the
solder trace from the center pin contact of external mike socket.  It
runs from just below mike socket to a small SMD resistor.  I soldered
a 2k resistor here and ran a tiny wire from other end of it, along the
side of radio and out a slot in case where the cover wouldn't pinch
it, and through the hole in the bottom.

    The radio now has to be operated by a power supply, since the
battery contact is gone and the wires are coming out the hole in the
bottom. I lengthened the power wire that was removed from the contact
and connected it to the same power supply as my TNC. The coax and PTT
wires go to the DB15 connector for the KPC-9612. I used the coax shield
for RX Audio as the ground connection, but left the TX Audio shield
un-grounded at the DB15.

    I am still in the process of evaluating how well this works on 9600
baud packet.  There are very few VHF 9600 baud stations near me (only
one, in fact) but hopefully in the future this will change.
Good luck, and I welcome any feedback about this.....

Gene, WA4WBI
=============================================================================

....rvz here again....

     I followed these directions, and receive works just lovely.  I've only
managed one connection though, not sure if it's a problem with the hookup,
or just my measly 30 watts not doing the job.  Much like Gene, I'm having a
hard time finding other 9600 activity close by.  Anyone know of activity in
the Northern 'burbs of Chicago?

    Couple of notes...  Although it's probably necessary to pull the front
off the radio just to identify the proper points, I made my connections on
the rear of the board that's exposed immediately after removing the back
cover.  Be careful with the routing of the rg174, paying attention to what
will be crimped when replacing the cover.  A friend smoked his when he
screwed the cover back on (what's an ERR 01 mean?), piercing the cable with
one of the ic pins.  I also didn't bother running the PTT cable out as Gene
describes.  I put a plug on the end of PTT lead from the TNC, and use the
microphone jack on the radio instead.

good luck,
rvz  N9ORG
-- 
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Robert Van Zant                                   Sevenex Public Access Linux
rvanzant@sevenex.sol.net                            414-843-4169 v.fc 24hrs
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