Saturday 15 January 2011

MultiBand Beacon Progress

After leaving undone those things which I ought to have done (beacon-wise) for too long, I finally sat down and did some PIC programming today...

I am now the proud father of another option on my menu system, which allows me to change band!

Not only does the new code allow me to display things like the image above - it actually changes the DDS oscillator too - but that's where things started to go bad...

My beacon signal generator uses a VXO system in which a 3.579MHz color burst crystal is pulled to generate the required frequency shifts. To run on 30m, my local oscillator signal from the DDS system is six-and-a-bit MegaHertz - no problem. However, to run down on 40m I would need a signal at 3.4...MHz - WHICH IS OUTSIDE THE RANGE which can be generated by the Si570.

I needed to take an alternative approach...

Fortunately the 7MHz signals can be generated by mixing my 3.5MHz signal with either another three-and-a-bit Meg signal OR a ten-and-a-bit Meg signal - so that's what I did!

Obviously, this results in an unfortunate "inversion" of the signal, such that my DFCW and Hellschreiber signals are seen "upside down" in ordinary QRSS grabbers. Here's a local Argo capture with a reflection to make matters (hopefully) clearer...

In essence, I'm now generating a lower sideband signal, rather than the original USB - I guess the answer is to flip my frequency modulations in the VXO upside down to right the wrong - that will have to wait for a while longer!

Also, I've not had a chance to get the WSPR emissions sorted on 40m as yet (they also are "upside down" and out of band). For the moment, signal reports for DFCW and S/MT Hell on 40m gratefully received!

...-.- de m0xpd

1 comment:

  1. Paul,
    I have seen your 40m signals the better part of the day over here in JO22da.
    Concerning your 3.4MHz DDS problem, what about generating your DDS frequency at 8 times the required mixing frequency and divide it by means of a ripple counter? OK, care should be taken to mix with a proper sinusoidal signal...
    73, Joachim pa1gsj