Equipment

Most of the experiments on 136 kHz at GW4ALG have been carried out using a homemade transverter (transmit and receive converter) and a Yaesu FT707 HF band transceiver, operating at 10 MHz.  The FT707 is getting quite old now, but has provided good service for several years.  (This particular FT707 was a gift from my late father-in-law, Donald W. Behnken, KA1LXO who had used it on the family boat prior to upgrading to a TS430S.)

Initial tests on 136 kHz indicated that 15 W RF from the transverter was not enough power to contact reliably those stations already running transmitters in the range 100 - 300 W.  In addition, my receiving system seemed to be better than those at some of the other stations I was trying to contact.  Having more power on transmit would enable me to contact those stations with less efficient receivers and higher local noise levels.

First out of the workshop was a 100 W power amplifer (PA) using Power MOSFETs that was based on a design by David Bowman G0MRF. (David's design is capable of producing a lot more than 100 W, but my 30 volt power supply was not!)

Next came a PA using a pair of 572B valves in push-pull.  These valves can still be obtained and will provide years of trouble-free service.  These valves will even survive the occasional mishap, such as when the antenna suddenly goes off resonance; or the loading coil catches fire.  (From personal experience of experimenting on 136 kHz, I can testify that such events do occur!) Semiconductor PAs are often less forgiving.

To deal with specific operating problems encountered on 136 kHz, other projects soon followed.  Click on the hyperlinks below to find out more about the transmitting and receiving equipment used at GW4ALG.