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Saturday, January 10, 2009

The QRSS Calibration Problem: A Proposal

Eldon's effort to be seen by the 30 meter online grabbers (see below) reminded me of the big problem I faced when I first built my QRSS beacon: getting my signal into the very narrow (100 Hz wide) QRSS frequency band. If you think crystal control will solve this problem, think again: Almost all of us are using crystal-controlled transmitters, but circuit and component variations can easily put your signal far outside the freq range that the grabbers are watching.

I was able to get into the band because I was able to find a conventional CW beacon fairly close in frequency to the QRSS band. I used IK3NWX on 10.141800 MHz. Knowing the frequency of this beacon (it was avalable on the web), I used the ARGO and Spectran soundcard programs to put my sigs where I wanted them to be. IK3NWX was useful because it was so close (within 2 Khz) to the QRSS band -- I was able to put both the NWX signal, and my target freq on the screen. Later, I built my "DaVinci Code" reference oscillator -- it serves as a freq reference that I can use (again, with Spectran) to get back in the band after working on my transmitter (for those times in which I can't hear IK3NWX).

It seems like a lot of guys in the US and Canada are now getting into QRSS. Many may face the same frequency calibration problem. Are the frequency readouts of the ubiquitous Kenwood/Icom/Yaesu rigs accurate enough to help? Do they go down to the tens of hertz range? I suspect they do not.

What new QRSS ops in the U.S. and Canada might need is the North American equivalent of IK3NWX's beacon. It should probably be fairly high powered (but 5 watts would probably do the trick). Conventional CW would be better than QRSS (it needs to be heard). The frequency should be outside but within 1-2 kHz of the upper or lower QRSS band edge. A station out in the Great Plains would probably be able to serve the large ham populations of both coasts. Perhaps we could arrange for the calibration beacon to be on at certain times (daytime on the weekends?). Of course, the key would be to employ a station with very accurate frequency measurement ability (down to 1 Hz) and a highly stable signal.

What do you guys think?

2 comments:

  1. Hi Bill,

    I've just been here with building a Pixie 2. David Rowe and I have just been tackling this problem.

    We built two Pixie 2's and they oscillate about 2KHz apart. Which is convenient as we don't need RIT, but not so good from the reproducability point of view. Nor is it going to be easy to build simple receivers and get them on the same frequency for QRSS.

    How do you calibrate it?

    cheers,

    Kim
    --
    VK5FNET

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  2. Bill,

    Probably a very good idea to have a reference beacon; but as you are writing it I am thinking to my self "how are they going to know exactly where they are?"; then you dropped that knowledge at the end.

    @Kim I am planning a Pixie 2 just for that purpose.. I'm hoping I can get things close enough with some form of variable capacitor in the oscillator circuit.. I plan to start with a grabber, but I know that with all the steps between now and then it will probably be 6 weeks before it is on the internet.

    Jer N1JER

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