Yaesu FT-220 Conversion to Four Metres
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This is the rig after removing the front panel and s meter etc. Below is the new mosfet linear PA stage which is fitted in the space vacated by the mains transformer |
Above are the front fascia, knobs, bezels and s meter ready to be re fitted after repair/cleaning. This is the finished transceiver. |
The block diagram below shows the sections requiring modification which are shown in purple. |
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Here is the new mosfet linear PA stage circuit.
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I bought this Yaesu FT-220 from the internet and it turned out to be a real "basket case".
It turned out to have numerous faults which required attention before any conversion to four metres could be contemplated.
After a couple of weeks the faults were rectified and the rig was tested on all modes on two metres, it was now time to consider how the four metre conversion would evolve.
As the rig is very rare in the UK and is nearly 40 years old no detailed conversion notes have been included here, just the gist of what I have done. The final specifications can be seen above together with the new PA circuit and the final appearance of the transceiver.
The original mains transformer and power supply pcb were removed as 13.8v dc operation is all that is required.
As there are no repeaters on four metres the original RPT button on the bottom left corner is now a "Transmit" switch and the green indicator below the "CLAR" indicator is a TX indicator. The band switch adjacent to the new transmit switch is now a power output control which varies the transmitter output from about 10mW to 60W. The original local oscillator box was removed and replaced with a 50MHz oscillator module. A directional coupler has been fitted so the front panel meter now also reads SWR as well as its original functions, SWR is shown on the meter for the first two seconds of every transmission after which power output is displayed.
Automatic final protection has been installed which protects the PA stage should the swr become excessive. Note that a 5 pole low pass filter has been fitted after the PA stage but is not shown above.
It has to be said that the amount of changes required in this conversion were many and unlike the Trio TS-700 conversions I would not do this again!
UPDATE, May 2012
I have now fitted a dc to dc converter internally to supply the 50v rail for the Mosfet output stage, the rig still runs 60watts but there is now only the one supply required, ie 13.8v.
It turned out to have numerous faults which required attention before any conversion to four metres could be contemplated.
After a couple of weeks the faults were rectified and the rig was tested on all modes on two metres, it was now time to consider how the four metre conversion would evolve.
As the rig is very rare in the UK and is nearly 40 years old no detailed conversion notes have been included here, just the gist of what I have done. The final specifications can be seen above together with the new PA circuit and the final appearance of the transceiver.
The original mains transformer and power supply pcb were removed as 13.8v dc operation is all that is required.
As there are no repeaters on four metres the original RPT button on the bottom left corner is now a "Transmit" switch and the green indicator below the "CLAR" indicator is a TX indicator. The band switch adjacent to the new transmit switch is now a power output control which varies the transmitter output from about 10mW to 60W. The original local oscillator box was removed and replaced with a 50MHz oscillator module. A directional coupler has been fitted so the front panel meter now also reads SWR as well as its original functions, SWR is shown on the meter for the first two seconds of every transmission after which power output is displayed.
Automatic final protection has been installed which protects the PA stage should the swr become excessive. Note that a 5 pole low pass filter has been fitted after the PA stage but is not shown above.
It has to be said that the amount of changes required in this conversion were many and unlike the Trio TS-700 conversions I would not do this again!
UPDATE, May 2012
I have now fitted a dc to dc converter internally to supply the 50v rail for the Mosfet output stage, the rig still runs 60watts but there is now only the one supply required, ie 13.8v.
