

        YAESU FT480R VARACTOR DRIVE MOD FOR 9600FSK AND 1200PSK
        -------------------------------------------------------
                     by Dave Hulatt G4WFQ
                     --------------------

For those of you who owning an FT480R and would like to be able to modulate
the varactor directly heres a simple mod. It will give you a much better
uplink on Fo20, Lusat and Pacsat. You will also be able to input 9600bauds
directly to the same point and be able to work UoSaT-3 aswell.


First of all make up the following simple small circuit.
                                     8vTx
                                     :
                     8vTx            :--------------
                     :         ------:------        :
                    47k       :      7     6:---:----------(to fm mod post)
                     :        :    ca3140   :   :   :
     Txa in----------.--------:-3           :   : ----- 100n
                     :        :       4   2 :   : -----
                    10k       :-------:---:--   :   :
                     :                :   :-----:   :
                     :                :             :
                     :                :-------------:
                     :                :
      Txagnd-------------------------------



Note pin 2 is linked to pin 6 on the ca3140.



Locate the so called FM modulator which is XM01, you will find that there
is a connector post nearby which you can apply the output from the above
circuit to. Then connect 8vTx from the post which is also nearby.
Keep the leads as short as possible. You will have to connect a switch in
the 8vtx line so that you can use the mic skt as normal.


Some component changes are needed to the modems.
G3RUH 9600 Modem :- change C34 for 470n or place in series.

G3RUH Psk Modem :- Remove R5, change R3 for 50k pot, change c9 to 100nf.

Set output of Psk modem for 500mv.

Nb. This will pull your radio off frequency slighly about 5 khz. Allow
for this simply by adding 5khz to your read-out.




Subject: FT480R 1200 BPSK and 9600 FSK


Modifying the FT480R for BPSK and 9600 FSK.
-------------------------------------------

I have modified my FT280 (Japanese home version of FT480R) for direct FM with
G3RUH FO20 modem. 
On the FT480R MAIN BOARD, connect a screened lead to FM MOD (XM01) .
On my radio there is a PINK/WHITE wire going to XM01 which is near the centre
front of the MAIN BOARD. This is the point that you want to connect in your
TXAUDIO.
You can connect the screen of the lead to the case of the XM01.

You will require about 2volts p-p at the FM MOD from the FO20 modem for 3.5KHz
deviation.
I modified my G3RUH modem as follows:- 
Remove R3 (270K) resistor and fit a wire link (0 ohm).
Remove C9 (10nF) and replace with 1uF foil capacitor.
Remove R5 (1K8) and replace with 22K pot. 
Take output from wiper of the pot. (TX Audio).

This has fixed the problem with poor results on FO20 with the Yaesu.

I have also tested it on 9600 FSK terrestrial with good results.

To receive 9600 FSK on the FT280/480R you have to take the O/P direct from
the FM RX discriminator. I picked this signal up from D11 on the MAIN BOARD.
I used a screened lead from D11 to a rewired mic socket:-

On Microphone disconnect orange Lead from pin 5 and solder it to pin 2
leaving pin 5 unused.

On the FT280 mic socket, disconnect link from pin 2 to pin 5 and connect the
screened lead from FM discriminator O/P D11 Anode to pin 5.


73 de David GM4JJJ @ GB7SAN
