
TS-790 & G3RUH.

                   KENWOOD  TS-790E   4800 baud operation.

These notes tell you where to get FM RX audio direct from the discriminator,
and where to modulate the FM TX directly.

ACC4 CONNECTOR
Two pins in the ACC4 connector are free to use: pin 3 and pin 5, pin 8 is
ptt and pin 2 is ground.

Remove the bottom cover only. You can now see the IF-unit. Remove all
screws and place the unit in vertical position. Now you can reach the
solder-side.

TX connection
1. Locate ACC4 = CN38.
2. Take a piece of shielded cable, solder the inner to ACC4 pin 5 and the
   outer to ACC4 pin 2 (ground).
3. Locate CN31. Solder the inner of the shielded cable to pin 2 (use ferrit)
   and don't connect the shield at this side.

RX connection
1. Locate ACC4 = CN38.
2. Take a piece of shielded cable, solder the inner to ACC4 pin 3 and the
   outer to ACC4 pin 2 (ground).
3. Locate IC 8 (MC3357P) on the IF-unit. Take a 10 uF tant. capacitor and a
   8k2 resistor. Solder the + to pin 9 and the - to one end of the resistor.
   Solder the other end of the 8k2 resistor to the ground.
   Now connect the inner of the shielded cable to the junction of the
   capacitor and the resistor. Don't connect the outer.

Put the IF-unit back in place. Be sure that all the smal coaxial connectors
are still in place on IF-unit !
Now you can connect the moden to the TS790E with the 7-pins ACC4 connector
supplied with the tranceiver.

At this time I only have tested this on 70 cm but this must also work on
2 meter and 23 cm.
Send remarks and/or suggestions to my home-bbs. Succes!

73's,  Bern PE1ABT @ PI8TMA or PI8UTR



  ADAPTING THE KENWOOD TS-790A FOR USE WITH THE PACCOMM MC-NB96 G3RUH MODEM
                                   12-26-91

 The Kenwood TS-790A makes a wonderful 9600 BPS Packet Radio Transceiver as
it
has an excellent front end, powerful transmitter, and 144,440, and 1.2 GHZ
coverage. The CFW-455F filter inside is not too narrow despite what you may
have read and coupled with the low noise front end of the rig enables the
G3RUH modem to reliably decode valid data that barely moves the S-meter.

 The modification discribed below is simple, reversible, and does not impair
normal operation or the appearance of the transceiver. This is a "no holes"
modification as it allows the G3RUH modem to be connected to ACC 4 jack on
the
rear panel.

 Place the TS-790A upside down on a soft clean surface so as not to mar the
cabinet. Remove the bottom cover to expose the IF. Board. With the front
panel
facing you the work area is the upper left quarter of the IF board. Identify
pin 9 of IC8 (MC3357P). There are two of these chips on the IF board but only
the main demodulator IC is in the work area. RX audio to the modem will be
derived from this point. Next locate J31 a two pin connector near D81 and X2
(10.965 OSC). TX audio from the modem will be supplied to the hot lead on
J31.
Note the large aluminum heat sink that spans across the IF board near the
rear
of the chassis. A round lug will be mounted on it near the rear of ACC 4
jack.

 Wire an eight pin din plug. Use shielded cable for TX and RX audio. No
traces
on the IF board need to be cut. Pins 3 and 5 of ACC 4 are not connected to
anything as the radio comes from the factory. Make sure the Din plug fits the
jack properly before wiring it.

PIN 2 - ground
PIN 3 - TX audio from G3RUH
PIN 5 - RX audio to G3RUH
PIN 8 - PTT

 Prepare two six inch lenghts of RG-174. Prepare one end of each cable so
that
the shield will reach the ground lug mounted on the large aluminum heat sink.
The cables will be routed over the top of the heat sink and will not be
crushe
when the bottom cover is reinstalled as there is adequate clearance.

 Solder the center conductor of one cable to pin 3 on the rear of ACC 4
(verif
with ohm meter). Solder the center conductor of the other cable to pin 5 on
the rear of ACC4 (verify with ohm meter). Dress the cable connected to ACC 4
pin 5 over to IC8 pin 9. Cut to size and solder (be careful- use minimum heat
and thin solder). The exposed shield is discarded and heat shrink tubing
place
over the end to prevent any shorts that would otherwise occur from having
exposed strands of the shield touching something. Dress the other cable
connected to pin 3 of ACC 4 to J31 and cut to size. Prepare the end in the
sam
manner as the other cable. Solder the center conductor to pin 2 of J31. This
i
accomplished by cutting the lead going to pin 2 about 1/2 inch back,
stripping
the insulation back 1/8 inch on the two ends, and then joining the center
conductor of the cable going to pin 3 of ACC 4 and soldering the three
exposed
ends together. Use heat shrink tubing to cover the solder joint.

NOTE that the banded end of D81 is not the cathode of the varactor diode !
There is no need to insert any additional capacitance in series with J31 pin
2
The shields are not connected at both ends of the RG-174 cables in order to
prevent ground loops. The Aluminum heat sink was used as ground as no other
ground was available that was close to ACC 4. Your sight may be better than
mind and you may find one.

 Adjust VR-1 on the MC-NB96 board for 75 mv p-p as measured on pin 2 of J31.
This will give a good initial setting for injected transmit audio level.

 This completes the modification. 9600 BPS Packet can now be enjoyed on each
of the bands installed in your TS-790A. For non-packet operation either
unplug
the modem from ACC 4 or turn off power to the modem. For 9600 packet
operation
unplug the mic and turn the mic gain to minimum.

 Thanks to Frank Anderson, W7ZTA and Jeff Angus, WA6FWI for their help.
Please
report any errors or suggestions to:

Mike Hooper
KF6PU @ WB6YMH.#SOCA
