Modifications for the Yaesu
FT-480
19-07-1998 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).
19-07-1998 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.
73 de David GM4JJJ @
GB7SAN
19-07-1998 FT-480R
VARACTOR MOD FOR 9600FSK AND 1200PSK
by Dave Hulatt G4WFQ
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.
26-09-1998 Low power in all modes for the
yaesu FT-480R
BY PE1RCS AND PA3FXW.
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.
73 de Teis PE1RCS and Robert
PA3FXW@PI8ZAA.#NBO.NLD.EU - QTH Nijmegen JO21VT