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Thursday, March 17, 2011

WSPR Direct Conversion Receiver: On the Air and Online

In a testament to the sensitivity of the WSPR system (and I mean that in the technical, not the emotional sense) I got a couple of reports indicating that my very QRPp WSPR signal was, well, a bit obnoxious. I think part of this results from the fact that I'm one of the few people using a double sideband transmitter -- the lack of filters makes my signal look a bit different. But I do have an AC hum problem that shows up on receive screens. And because I haven't worked out the circuitry to allow the WSPR software to move my little transceiver from transmit to receive, I'd been leaving it in 100% transmit mode. I can understand why people didn't really like that.

So, on the theory that it is better to give (reports) than receive, and in keeping with the old idea that all ham radio stations should from time to time RELEASE the push to talk switch and LISTEN, I have magnanimously taken my homebrew DC/DSB WSPR system into receive mode. I'm in 0% transmit. I'm listening all the time, and automatically uploading reports on the stations I hear. Pictured above is the map from WSPR system page showing my spots from last night. Below you can see what my own WSPR system display shows. (I need to adjust my W3PM oscillator a bit. I may be a few hertz off and I am probably missing a bit of the 200 hertz wide WSPR band).

I was pleased to see W3PM's call on my map. An article by Gene provided the inspiration (and much of the circuitry) for my WSPR rig.

My receiver is very simple: The RF from the antenna goes through a low-pass filter directly to an SBL-1 mixer (thanks to Jim -- AL7RV). There it mixes with LO energy from the W3PM Colpitts oscillator. From there it goes to the KA7EXM discrete component AF amp.

You can watch -- almost live -- the stations I am receiving by going to
just type N2CQR in the box that asks for the call.

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