To be honest, I think those who only transmit are much to be despised (hyperbole for effect). We beacon experimenters owe a debt of thanks to those who spot and grab our signals - in my case that's a particular thanks to Guenael and Johan and others - and the best way to repay that debt is to play our own part in the reception and reporting of the signals of others. This is, after all, a street with two-way traffic!
So - I decided today was the day to cook up a receiver for my beacon.
I took as my jumping off point the excellent DC receiver section of Roy Lewallen, w7el's, Optimized QRP Transceiver for 40m . I had already enjoyed success with this circuit, having used it as the basis for the receive side of my Funster Plus rig. Now all I needed to do was modify the AF filter to give a passband in the 1.5kHz region associated with WSPR signals...
This was quickly achieved with an LTSpice model...
which offered the required frequency response...
Now I've got the "free" toner transfer process down to a fine art, it is (almost) simpler to go straight for a PCB, rather than mess around with any other processing method - so EAGLE gave me a layout in no time...
but is still took an AGE to drill all those pesky holes...
Once the board was stuffed I was too excited to make tests or anything as organized as that - I just connected up the minimum set of elements on the bench and took it for a test drive...
You can see the new Rx board at left, with the Si570 USB Synth above it and the Low Pass Filter connecting to the antenna at right.
Here's a closer view of the new Rx board doing its thing...
Sure enough, I started spotting WSPR signals - the first from pa2wo.
The AF gain of the receiver isn't high enough - I can only get an Rx noise level of -25dB on the WSPR screen at the moment, but it still pulled in some signals...
I'll leave it running overnight and see what I can catch - despite knowing that the overall gain isn't high enough yet. Perhaps I'll sort that out tomorrow.
...-.- de m0xpd
Update:
As promised, I left the receiver on overnight with the following results (ten different stations, all spotted in the evening (nothing after 22:15 UTC)...
Not very impressive! I must try and make some improvements today - but first I've got to fix the bottom of the workshop door, which is showing signs of age!
Hello, Paul -
ReplyDeleteHave you considered using a "Norton Amplifier" - in particular the venerable LM3900 (quad amp on a chip)? Ten-Tec used it as a bandpass audio filter in their Century 21 QRP rig and it seemed to work quite nicely. They used 3 of the 4 amps on board for 2.5, 1.0 and .500 khz bandwidth - switching in one, two or three amps. Check out
http://www.scribd.com/doc/31890363/Ten-Tec-Century-21-Owner-s-Manual on page 20. I think you could change the filter r-c components and get it just about anywhere you wanted - additionally, there's plenty of gain. Do a search for "LM3900 data sheet" - gobs of info is out there, just waiting.
Best DX with your WSPR
Bruce - KK0S