Modifications for the Yaesu FT-780
Modification of the Yaesu FT-780/FT-480 for 9600 bps use
The necessary modifications of the FT-780 R are quite simple. All
connections can be made without removing the main PCB.
The receiver AF *MUST* be taken directly from the discriminator. A
suitable point for this is the cathode of D02. This part is soldered
in with the ring to the top. If the transceiver is so positioned that
the tuning knob faces towards yourself, D02 is located in the lower
right of the PCB, near the ceramic discriminator, a small grey box,
abt. 5 mm x 5mm big).
The transmitter AF is to be fed to the upper left pin (refer to the
circuit diagram!) of the modulator unit. This point is also acessible
without removing the PCB. Just above of J9 there is the resistor
R 265 (labelled C 265 in my unit, 10 kOhm instead of 4.7 kOhm). You
have to remove the varnish of the upper lead of this resistor. The
TX AF is to be fed to the upper lead of this resistor.
The normal voltage level from the microphone amplifier at this point
is about 2 Vpp (just not clipping). The value should be adjusted by
VR1 of the G3RUH-FSK-modem.
Both points can be found in the circuit diagram, part "MAIN CIRCUIT".
The only question that should be left is how to get these two points
to the outside of the radio. I decided to give out the possiblity to
switch the 1750 Hz tone from the microphone (not used in US versions!).
I gained two line at the microphone plug.
For testing purposes, a 60 kB text files was transferred. There were
no retries. Reception of UO-22 and KO-23 is possible without any trouble.
Even if signals are weak (AOS/LOS), decoding works well.
vy 73 de Hartmut DL1YDD @ DB0IZ.DEU.EU
Be careful when using this information on "Sommerkamp" radios.
They may be different (like a FT480 I saw recently).
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