Improving 50-MHz Transmit Capability
Over the past week in the evenings, I’ve managed to cobble a little PA together for the 50-MHz transverter. It’s a near-clone of the PA in the Elecraft XV50 using the Mitsubishi RA30H0608M. Last night, I got it all hooked up and installed in the cabinet. It broke into oscillation when keyed on CW.
The oscillation was about 50.040 MHz. I reasoned that it might be the PA output coupling into the nearby TX RF bandpass filters which are followed by 12 dB of gain before returning to the PA. So, tonight, I added a litle shield between the BPF and the PA board. That seemed to clear things up and I got about 10 watts out. There is a 6-dB pad between the last driver stage and the PA, so I should be able to get it up to about 18-20 watts. But, the first goal will be to check the linearity on SSB.
In other transmit capability news, some boxes and heatsinks arrived for the W6PQL PAs for 903 and 1296 this afternoon.
Those modules are great but they often oscillate like you noticed. The shields are a good idea, but I’d also add additional good quality (like ATC or equivalent) chip caps to all power and biasing lines.. in worst cases a ferrite bead on the power lines are needed.
But I think it’s great that you are hombrewing your own transverter. It’s a lot of fun. I’ve done that on 432 and 2304 MHz. I’ve also built various generations of DEMI and Ten-Tec transverters for 50, 902, 1296, 2304, 2400, 3456 and 10368 MHz. Great fun.
Fred, thanks for the hints and encouragement! Aside from power modules and perhaps some helical filters, I have the parts to build similar transverters for 222 and 432. But, my enthusiasm for homebrewing may have waned a bit by the time I get to them. Next goals are to finish 50 MHz, which is very close, then get the W1GHZ stuff finished for 1296, then 903. That’s probably another month or two each at the rate I’m moving. Right now, I’m planning to stop with 3456, and there’s lots to be done on 2304 and reviving the 3456 rig sitting here. So, the borrowed FT-736R will soldier on on 222 and 432 for now!