23 Jan 2013

New 137kHz Transverter thoughts

This evening, I've ordered a reasonable sized heatsink to use with the new 137kHz transverter. I am aiming for a power from the transverter of at least 30W and want to be sure that with mismatch the PA is able to survive quite hard abuse. The IRF640 looks a good choice for the PA, maybe a pair, as it is rated at a high voltage (200V) and high current (18A) so I can run the PA from a 30V (or even 50V) supply to get more out. Even with 30W RF, the ERP will still be in very low milliwatts.

As I want to ensure the 10MHz LO signal is very stable so I can use it with WSPR-15 and QRSS30 modes, I may put this in a separate insulated enclosure and pipe the injection signal in via coax.

What I am most concerned about is the lack of activity on the 137kHz band: the last time I gave it a go with WSPR the biggest issue was the very few people actually monitoring WSPR on the band. At the moment, the new 472kHz band is very much the focus of attention with up to 50 WSPR users monitoring and/or TXing on any evening. On 137kHz however the number of WSPR users is often just 3 in the world with no-one on in Europe at all.

Still, I am convinced that with WSPR-15 I should be able to reach near Europe even with my 20m earth-electrode antenna if I can get the power up to around 30W from the transverter. It may even be possible, just, with WSPR-2.This is worth a go, before getting back onto other projects ...like finishing off the Tenbox transceiver!

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