Modifications for the Yaesu FT-480
FT-480 & 9600 Bps
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).
FT-480R 1200 BPSK and 9600 FSK
I have modified my FT-480 (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
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
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.
FT-480R VARACTOR MOD FOR 9600FSK AND 1200PSK
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.
: ------:------ :
47k : 7 6:---:----------(to fm mod post)
: : ca3140 : : :
Txa in----------.--------:-3 : : ----- 100n
: : 4 2 : : -----
10k :-------:---:-- : :
: : :-----: :
: : :
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.
Low power in all modes for the yaesu FT-480R
The FT-480R has a low power switch, which reduces power output on CW and FM to
1 watt. Unfortunately, this has no effect on SSB. If you want to run the 480
on reduced power (e.g. to drive a transverter) this modification might be of
If you look at the schematic, you will find out that switching to low power is
done by reducing the voltage on pin 2 of the power module (M57713), probably
the power supply of the power module's driver stage. The variable resistor
VR1012 on the main board controls the power level on LOW, if desirable down to
milliwatts level. When the LOW switch is depressed in CW or FM mode, this
switch will ground the base of the voltage control transistor through VR1012
and a diode. (there is some other circuitry involved but I omitted it for
reasons of simplicity). However, in either USB or LSB this switch will NOT
ground and leaves the transistor's base floating to +13.8V, just like it does
when the switch is not depressed at all.
By adding a simple wire between the switch ground and the 480's ground, low
power will also be effective in SSB. Open the transceiver, locate the front
pcb and solder side of the LOW switch, find out the switch ground with a
multimeter (measure a diode in CW or FM and high resistance when in SSB mode)
and solder an insulated wire between the switch ground and "real" ground.
On-the-air tests have proven the modification to work excellently, although it
has not yet been tested on a spectrum analyzer to check for possible intermods
(there must be a reason why them clever Japanese cunningly left out SSB on low
power??? Lowering voltage on a driver stage will usually affect linearity!)
But there is more... Did you know there is an external TX control available,
one of the four small pins located on the underside of the 480 gives +13.8V on
transmit, excellent for external relay or transverter control! These pins were
meant to control an external CTCSS unit.
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9th February 2000
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