Modifications for the Yaesu FT-480

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

P.S.:
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 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.

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.

                                     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.
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 some use.

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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