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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Modifications for the yaesu - Read Book - TheHQBooks.com
