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Var output power mod

This page was last updated : 11-Mar-20 23:08:54

Yaesu FT-221R variable oputput power mod

One thing is don't like is to use the maximum output when not needed. For local QSO's I have with other amateurs in the area I life, using the 18 Watt (yes the rig had a extra power mod in it) is overkill. Searching the Internet I couldn't find good information about it, but fortuanatly a local ham was kind enought to digg through is huge paper archive to look for some and came back with a power mod for the FT-221R using the Exciter unit (PB-1466).

Although you can use any variable resistor for it, I used the RFGain variable resistor because I don't use the RFGain anyway.

The mod is show below.

The black and white wire connected to pin 9 of the exciter board is solderd lose as the same fo the capacitor of 1nF. Solder the kathode of a diode (for example a 1N4148) to pin 9 of the exciter board and solder the 1nF and the black and white wire to the anode of the diode.

Now modify the connections on the RFGain variable resistor.

1. part : Main part of the variable resistor (the one with 3 wires connected). Put the RFGain in the MAX position and measure the values between the inner and outer pins. For my rig I solderd the white/yellow and the white/green wire together (the are 0 ohm together when RFGain is max) and solder a 500 ohm (499) resistor to it. To the other end of the resistor I solderd the yellow wire and packed verything up in heat shrink wrap.  (Please check you're wire colors because they may be different in you're rig).

2. part : Second part of the variable resistor (the one with 2 wires connected). My rig didn't have any resistance between the wires in the max position so I just solderd them together and packed them in heat shrink wrap.

3. part : clean the RFGain variable resistor and solder the 12K resistor to the center connector, the 1K ohm trim resistor to one of the outher pins, and the 10K ohm trim resistor to the other outer pin.

Here are some photo's of the mod.

The black wire is connectod to ground, the brown to the +8V (taken from pin 12 of the FIX unit), the orange to pin 9 of the Exciter unit.

When everthing is solderd and checked connect a power meter and swith on the rig. Pushing the mike in FM will give the max output.

A good start is to put the  trim resistors in the middle position and turn the RFGain (now HFGain) to the max, trim the 10K trim resistor so the power is just droping and trim a little back. Put the RFGain (now HFGain) to the minimum and trim the 1K trim resistor so the power is just rising (you mide have to repeat the above a few times).

Photo below is showing the CTCSS module with his PCB in the background, in the foreground the 500 Ohm resistor replacing the main part of the RF gain variable resistor (the white/yellow + white/green, 500 Ohm resistor and the yellow) and the connected wires from the second part of the variable resistor (the 2 black wires with shrink wrap around it).

All back in place.

Photo below is showing in the foreground the installed RFGain (now HFGain variable resistor) needly packed in ducktape. The 500 Ohm resistor replacing the main part of the RF gain variable resistor (the white/yellow + white/green, 500 Ohm resistor and the yellow) and the connected wires from the second part of the variable resistor (the 2 black wires with shrink wrap around it).

Not complety factory design, but it wil manage.

And it works like a charm. Now the output power is variable from 50mW to the full 18W.

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