Hi John de Richard in London. Herewith modification information on my gear.

IC-251. Digital modulation applied to left-hand end (anode) of varactor diode
        (D11) at the junction with C52/53/R57 (just below Q13 on circuit
        diagram) as below. Modulation voltage from standard G3RUH 1200 bps
        modem wasn't high enough but was boosted by component changes on the
        modem board. Voltage from the G3RUH 9600 bps modem is fine with the
        output level pot set to about a quarter of a turn clockwise from its
        end-stop. Info originated from JA1QHQ. JMP's 1,3,4 ON.

                                 10kohm         D11
       connect audio sig.    ---\/\/\/\/\------>||------

        PTT connection made inside the rig to the appropriate pins on the rear
        panel's accessory socket - no complications here, my TNC's PTT comes
        from a reed relay.

        No modifications done for digital output from receiver (yet).

        Have investigated modifying to provide up/down control but checks are
        incomplete. Suspect provision of this facility is possible and have
        identified (display) DRIVER IC2 pins 3/11 as the likely place to
        apply it.

        Once AO-21/Rudak starts with higher speeds I'll probably expedite the
        provision of receive output and up/down control.


IC-471. Digital output taken from discriminator (IC-14) pin 9. This pin, and
        ground, are brought out to J-14 for feeding the optional tone squelch
        unit (not fitted on my rig). Rig works well with existing CFW-455E
        filter (I think its 15KHz bandwidth) but needs retuning after about
        4-5 KHz of doppler; a wider filter may require less frequent tuning
        but, with the advent of 12.5 KHz channel spacing on terrestrial uses,
        I kept the narrow filter.

        Digital modulation would be applied, as with the IC-251, to top of
        the deviation pot; thats at the junction of R28 and R29, close to Q1
        on the circuit diagram. I haven't actually used this yet (see note
        above about RUDAK).

        PTT connection made to the appropriate pins on the rear panel's
        accessory socket - same story as IC-251.


Connections made to both rigs via phono sockets using screened cable both
inside and outside the rig. The IC-251 has some unused sockets, and the IC-471
has a removable plate which I mounted 3 sockets on.

The IC-471 provides receiver audio on pin 8 (the centre pin) of the mike jack.
I modified the IC-251 to put it on the same (previously unused) pin. This is
used for "ordinary" 1200 bps operations. Pin 4 of the IC-471's mike jack is
the up/down line; that pin is unused on the IC-251 so I'll probably use it
if/when I modify the 251 for up/down.

73 Richard G3RWL