16 Dec 2009

Idea for a simple 10m WSPR transceiver

GQRP club sells  inexpensive 14.060MHz crystals and these doubled would come out on 28.120MHz. I am wondering if they will pull UP to 28.1246? If so, they would make a perfect source for a DSB WSPR transceiver. Half the TX power would be wasted on a signal 3kHz lower but it would be a very simple design with just an oscillator, doubler, balanced mixer, PA and low pass filter, plus the basic audio input and DC receiver parts, which would re-use much of the TX design. Some experiments are needed!

Alternatively, can anyone suggest a more modern approach such as using a programmable reference oscillator as used in SDRs? What is the best one? Where do I get them from?


g4ilo said...

I get the impression that most people who are not using programmable oscillators are using a PIC chip preprogrammed with the table of frequency shifts to VXO a crystal. Either approach would avoid wasting half the power by radiating a redundant signal, and you wouldn't need a computer to generate audio either.

Paolo said...

I would double a 14.060 MHz XTAL and either pull it +2.3 kHz (in case use a Super-VXO) or play with WSPR 2.0 "BFO" setting.

The latter will move down/upwards the RX frequency window, while the TX frequency can be manually set outside the usual 200 Hz window in the proper main window field.

There's already a WSPR DSB signal on 30m, but I'm sure you already know who he is, HI.

g4ilo said...

I should have added that the 14.060MHz crystal in my QRP Kits DC20B and the one I bought as a replacement in a pack of QRP crystals on eBay both oscillate at about 14.062MHz in the DC20B circuit, which has been a source of frustration. I have just checked and it is currently on about 14.062.630KHz. I can definitely pull it until I hear a 1.5KHz tone with the RX in USB and tuned to 28.124.60. I could send you the other one but it has very short leads having been mounted on a PCB - drop me an email with your address if you want it.

Roger G3XBM said...
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Roger G3XBM said...

Thanks for the suggestions. I shall try to see if my 14.060 xtals will pull up a couple of kHz. This is the easiest approach I think. The idea of using a couple of xtals in a super-VXO to give me more pulling range is a good one.