The following instructions tells you how to make the right connections to an
ICOM IC-3220 in order to be connected to the G3RUH 9600 bauds modem.
The following steps are not very dificult to follow, but are to be carried
by a person with a minimum experience in electronic radio equipment.
If you are not such a person, ask to a friend with the required knowledge
to do the job for you. Otherwise, permanent damage to your rig can result.!
Also, (evidently), this manipulation will invalidate the rig warranty, so
perhaps you prefer to wait till the end of its validation period...
The author of this note is in no way responsible for any damage that can be
caused to your equipment by doing this modification to it.
Do it at your own risk, and think twice before begin !
(n) = Number of screws.
Material required: Screwdriver, Solder Iron, Coax cable (see text)
End of installation.
Remove (4) the BOTTOM cover. (the one without the speaker).
Remove (4+2) the shielding plate covering the P.A. output module.
Remove (2) and discard the bottom small plate covering the hole
behind the antenna coaxial cable. Restore the two screws in place,
just to store it for the future.
Locate connector J2 (The white big one, near to front panel) which
is used to interface the two main boards. (16 pins).
Locate pins 1, 2, and 15 of J2. Pin 1 is the nearest to the box side
of the rig. Pin 15 (the one before last) is located about the middle
of the main board.
1 - UHF TX stage modulator voltage input.
2 - Ground.
15 - UHF RX detector output.
If in doubt about pinout, see schematic diagram (Main B unit, left hand)
Take two pieces of SMALL diameter coaxial cable, (Z:50 ohms preferred
by me, but ordinary AF coax cable will perform pretty well).
Aproximate diameter MUST be no more then 4 mm, and lenght as required.
Following Murphy's law be generous ...
Join the two (outer) shield parts of coax cables and solder them to
pin 2 (ground) at the upper (visible) part of J2. Solder the inner
(active) part of one cable to pin 1 and the other to pin 15.
Soldering should be performed to the upper part of J2 with
EXTREME CAUTION, as the plastic support structure of J2 connector,
can be seriously damaged !!!.
Route the two cables trough the main board, up to the hole near the
antenna cable, routing them in such a way, that traverses the small
square hole at the bottom part of the plate covering the final P.A.
Secure the cables at the output hole with a BIG plastic strap.
Reinstall (6) the cover of final P.A.
Reinstall (4) the bottom cover of the rig.
Solder appropiate connectors at the other end of coax cables.
With this modification, only the UHF part of the rig is affected,
i.e. the mod will only work for the 432 Mc/s. band.
Also, some noise has been observed at RX detector output line, which make
the DCD led of the TNC blink, but this does not affect the overall
performance of the assembly.
As a guide, using the french TPK program, a serial (rs232) speed of
19200 bds, the well known G3RUH modem, and a standard TNC, a file of
1.5 Mbytes has been transmited in one hour, obtaining and average speed
of 364 cps. (TPK measured).