Bulletin: SM470
Vendor:   Yaesu
Subject:  FT736  DIRECT VARACTOR FM MODULATION


Refer to the circuit diagram; inject your TXaudio at the junction of
R32/C29 on the TX Unit.  The signal level at this point should be 800 mV
peak-peak, and will give +/- 3 kHz deviation.  DO NOT EXCEED THIS LEVEL.
Set Mic Gain to min.

Modulating the FM transmitter this way you get an LF response down to
18 Hz (at which point the associated synthesiser PLL begins to track the
modulation), and an HF response which is flat to some 10 kHz.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. TX Unit is the module flat on the left (not the one tucked down the
    side vertically).
 4. R32 is just to the left of the rectangular shielded enclosure.  The
    resistor is "on end".  Scrape any paint off the free leg.
 5. Your TXaudio lead should be a fine screened cable;  connect the inner
    to R32, and the outer braid to the adjacent enclosure.
 6. Route the cable out though any convenient aperture in the case.

 7a. 1200 BAUD PSK MODEM: TXAudio of 800 mV pk-pk can be obtained by
    adjusting the components C9= 1uf, R3=47k, R5=infinity (i.e. remove).
    C10 stays at 10nf (0.01uf).

 7b. 9600 BAUD FSK MODEM:  Adjust TXAudio level with VR1.  Use TXEPROM
     selection number 10 (ten) for UO-14, i.e.  JMP1,3 ON, JMP2,4 OFF


Tidy Installation
-----------------
I found it neat to make up a little aluminium bracket to affix under
the rear left lid screw.  This bracket carries a 5-pin DIN socket,
and the TX RX and PTT wires are terminated here.  This saves having
leads dangling out of the interior. (Tnx EI6EH).