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The modified MF Solutions Transmit Downconverter for use on 137 kHz

– Posted in: 2200 Meters

My original plan was to build a simple CW transmitter for use on 137 kHz.  There are not a lot of simple designs out there compared to what is available for 630-meters that use inexpensive RF devices to make power and I really didn’t want  the responsibility of several hundred watts of TPO, which would translate to tens of thousands of RF volts at the antenna.  Its still unclear just how much voltage I can stand off!

I recalled a conversation with John Molnar, WA3ETD / WG2XKA, one of the founders of MF Solutions who builds the inexpensive transmit downconverter that I use on 630-meters.  John had done some work to modify the 630-meter transmit downconverter for use on 137 kHz and had good success with a few changes to the PA section.  When I decided that I wanted to begin making preparations for 2200-meters, I asked about  the modification and John was happy to help.  The modifications are pretty easy but if you want to operate 2200-meters, I recommend you buy a second board as trying to modify the system is a little more involved than a simple part swap.  Its definitely not a dual band situation.   I bought and built another board and have dedicated it to 137 kHz.  So far, so good!

MF Solution Transmit Downconverter modified for 137 kHz

The MF Solution 630-meter Transmit Downconverter modified for 137 kHz

This board will give me CW, which is what I originally wanted, plus the non-linear digital modes with power output up to about 10-watts at 13.8 volts.  I feel safer trying out 137 kHz at virtual QRP TPO levels and I can add an amplifier later if I desire.  Having the digital mode capability, I can do a better job evaluating my system using WSPR.

For details on ordering a converter and modification components, contact John Molnar at WA3ETD@gmail.com or call the phone number listed on his product flyer.

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