Thursday, 25 October 2012

SAQ UN Day Transmission

Feeling atrocious all night at work, despite the joys of pizza and free doughnuts provided by management. Mostly this was due to having a cold, but also the hassle of having a pocket of transmitters on the south coast failing due to incoming RBR failure. A nasty little high pressure pocket was causing tropospheric ducting all night, in fact i think the lads dealing with the final DSO had an easier time.

Coming home, and with the prospect of plenty of tasks in hand from Julie being away and the boys to look after, I decided to stay up for the UN day transmission from SAQ Grimeton. It was my intention to try an E-Field probe antenna for this, which i had started constructing the day before, having done the case work, layouts etc, and aquired the parts. As a 'back-up' I quickly strung a 45m longwire, which was only a few feet high, draped over things in the garden. This fed the laptop and Wolf DL4YHFs Spectrum Laboratory software, via a simple protective interface to the soundcard.

Well, the longwire ended up being the primary antenna, as when tested the E-Field probe drew nearly 50mA, sent the battery flat, and didnt receive! So, with the longwire set up,  I watched and listened for SAQ. When they began tune-up, I could just make out a signal. Of the transmission, I could make out a few V's being sent, but nothing more. This was disappointing, and probably due to the antenna being low and local noise. I need to get Sam to help me rig a proper long wire high up, to feed his receivers and the FRG-100, and also the VLF systems.

It turns out, that in my weakened, fatigued haste, I had misread the pin-out of the J310 FETs, and fitted them both backwards. Although the J310 has interchangeable source and drain, sadly the gate isnt!. Anyway, once these were refitted (not an easy job) the unit now only drew 5mA, and provided a signal. Phew, I hadnt killed the FETs. The signal was quite a bit weaker than on the longwire, GBZ from Anthorn was visible but nowhere near the strength as on the wire, but then, the wire was 45m long, and the E-Field probe antenna just a 1m whip!

All that remains, is to find a tripod or spike to fit the probe to for proper use. I do however, think its rather a nicely built unit

Heres an internal view, the circuit is build dead-bug, which is great for a simple circuit, until you need to fix it! I need to stick a bit of foam in to keep the battery from moving.

Slightly blurred photo, but this is the completed unit. Signal out from the 3.5mm Jack, BNC for the antenna whip, Ground terminal, and of course an on/off switch.

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