Wednesday, 5 February 2014

Plug 'n' Play-up

My previous post stated that I was getting no 'heard' spots on WSPRnet, but early this morning, that became a false statement. I heard a couple of US stations, but only just. Having been up all night, and then having a hospital appointment ah half ten, by the time I got home there was no point going to bed, so I took a look at the beacon.

After a fair bit of playing and head scratching, I realised it was a noise level problem. But fiddling with the soundcard settings didnt help. After a bit of fiddling, including being told by WSPR that my 'output device was invalid' (eh? I wasnt even touching that!) I found that the soundcard was set for microphone input (ok) but WSPR was set for Line In (ah!). I tried swapping to use the line in socket but that didnt help, so rejigged everything to actually be on the microphone input! Suddenly, with the mic gain at 0, I had an almost decent noise level, just hovering on the limits of the yellow section around 19-21dB. Suddenly my ears were syringed! Spots started to bang in and fill up the waterfall.

I tried my mocked up level controller, but it seems to have no effect! Im not sure what can possibly be wrong with  what is essentially a potentiometer with a plug and a socket attached, although maybe the choice of 100k is a bit too high? I'll test it later if im not too tired after Karate.

Some of the various parts ive ordered recently came today. Amongst them are the stereo jack sockets and the modem cards for dimantling

These are simple PCI cards and have a surprising number of salvagable bits on them. As well as the transformers they were bought for, theres a 47W class relay, a buzzer, a little crystal, probably 32kHz, some 1N4000 class diodes, and a smattering of capacitors. Plus the antistatic bags they came in will be handy!

The extra 32GB of microSD memory for Sams Android tablet came as well. £16 that cost, thats 50p a GB! I still think of myself as reasonably young, but I remember when memory was a £ a MB! And it came in a black rectangle with sharp pointy legs the size of half a breakaway biscuit! This memory for Sam is the size of my little fingernail, and most of thats the package!

Of greater consequence to my WSPR efforts, one of the items that came was the first of my USB sound cards. At £1.50 including postage, it was worth the gamble (the other one, coming from Hong Kong, cost 99p inc shipping, and is most likely identical!). Plugging it into a spare USB port on the back of the PC, the green LED lit up, well, thats a good start!

Instantly, Windows 7 saw it and started looking for drivers. Within a minute, it said it was ready. Ok then, so far so good, lets see how it actually performs.

A bit of changing in the WSPR software to make it look at the USB mic input (still on the on-board PC sound for Tx) and a few minutes playing with the Windows volume control panel, renaming the device so I can tell the difference between it and the on-board sound, and I put WSPR back to active and waited...

... MASSIVE noise level! +40dB! Luckily, I had anticipated this. The mic gain was set to zero, but I had noticed an AGC control was ticked. I unticked it, and the noise level dropped back to 20dB, just in the yellow. Ive had the WSPR software running on this now for 25mins, and theres plenty of received stations. So, its performing at least equally as well as the PCs on-board sound as far as receive goes. The 20dB I think is due to the radios output being just a tad too high.

Next step then, is to try the transmit side and see how this little beasties headphone output performs.

I have found a simple little 28MHz linear amplifier circuit to build, which should give me a bit of a kick on 10m WSPR when I get Wispy working. Its about 10dB gain, so with the Wispy giving its designed 200mW it should give a nice cool running 2W DSB signal, for an SSB equivalent 1W of USB WSPR. If I can find how to ramp the Wispy output up a bit to 500-1000mW DSB, then I can happily run a bit more power. I just need to get hold of a VN66AF MOSFET before I can start building, as its built around this device.

Something I noticed last night whilst updating this blog, was that my posts seem to be attracting at least one reader! It seems there possibly is someone out there who has so little else to do they are prepared to read my mindless ramblings! Whoever you are, feel free to comment, even if just to say hi!

UPDATE! - Found a suitable moment to put WSPR to idle, then set-up ready to test the USB sound cards headphone channel (Tx). Everything ready, clicked Test - No output. OK, stop being thick, and this time remember to change the plug to the new soundcard! That done, fired up for test into dummy load, and carefully set for 2W output. Bit tricky, as I think the level control pots track is damaged, either that or its a log pot! (quite plausible). With the level set to 2W, I set WSPR back to receive, and went off to put the kettle on. A few minutes later I returned and was curious why the receive noise level was 0dB!? Oh, try switching back from test load to antenna! This I did, but not before i'd heard EI6KH on the test load!!!

Now running the beacon entirely via the new USB £1.50 (inc postage) sound card. I wont decide if its good until ive seen a dozen or so transmit cycles out, but already ive five hearing and two heard by spots, and thats just one transmit cycle and a bit of fiddling so far!

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