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FT-847 and CAT control



          FT-847 and the UNI-TRAC system.

The FT-847 does not in its present state allow fully automatic
operation when tracking the 9600 baud AFSK satellites.

Yaesu state that the equipment is "9600 baud" compatible. This
is true with respect to the RX and TX audio from a modem being fed
to the varactor, and from the discriminator, without pre or de emphasis
modifying the audio signal.

The FT-847 has a front panel menu display selection of what is
termed "PKT RATE" which selects either the "1200 or 9600 mode".
(This should not be confused with serial communication 9600 baud rate)

Unfortunately the user CANNOT select the 9600 mode via the menu
and assume that the condition remains permanent. The "PKT RATE"
mode defaults to the 1200 mode.

This is especially true when using the CAT (Computer Aided Tuning)
facility. Immediately the initial command to invoke CAT control is
sent,  the "PKT RATE" defaults to 1200 mode and although you are able
to receive 9600 baud data from the satellite you are UNABLE
to pass TX data into the the FT-847.

This is fine if you are content to use your tracking system and
reset the "PKT RATE" menu to 9600 mode  AFTER the CAT control has
started the receiver tracking the doppler shift.

I have modified my FT-847 to overcome this problem.

Get out your schematics and select the AF_CNTRL_UNIT page.

Trace the leads up from the Packet socket to Q1040. R1140 (22 kOhm)
and R1147 (1 MOhm) are close by.

R1140 is located on the bottom layer of the PCB near the Packet socket
and MUST be REMOVED. (It is a tiny surface mounted resistor.)

A miniature 100 KOhm 10 turn trimming potentiometer, configured as a
variable
resistor, is paralleled across R1147.

The 100 KOhm pot is adjusted so that sufficient gain is allowed for
the TX audio to provide correct deviation without the gain being
too great so that the following peak limiter Q1048 does not inhibit
the 9600 mode PTT action. I have set this gain up to  a reasonable figure
so that the external gain controls on my various TNC, DSP, etc can
be externally adjusted individually for correct deviation.

You can now forget the "PKT RATE" menu control and have full automatic
unattended ground station control of both the 1200 and 9600 satellites
with the UNI-TRAC system and ZL2TPO/G7UPN WISP program.

BTW we have in ZL a product called "solder wick". This looks like
the braid one sees as the outer of coxial cable. The braid is soaked
in some sort of flux. Placing the braid on the area associated with
surface mounted components and applying the soldering iron heat sucks
up the solder into the braid and often the component undamaged.


An overview of the UNI-TRAC system can be seen at

                        http://www.qsl.net.zl2amd/

73

Dave Lamont      ZL2AMD      lamontd@clear.net.nz




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