I am now the proud father of another option on my menu system, which allows me to change band!
![](http://2.bp.blogspot.com/_71-IkTH3uDw/TTHirPLi8BI/AAAAAAAADjs/ODC3sQba_Yg/s400/40m%2BOperation.jpg)
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...
![](http://3.bp.blogspot.com/_71-IkTH3uDw/TTHlmDXTR_I/AAAAAAAADj0/qNt_zQ-XVmA/s400/Reflections.jpg)
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
Paul,
ReplyDeleteI 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