Peter,
it is interesting to look at the WW2 German radio equipment -
obviously designed pre-1939. The use of ceramics, especially in
capacitors, and iron cores is interesting, to say the least.
I haven't had the chance to look into any such equipment. The only WW2
vintage equipment I have ever gotten my hands on is American.
Nowadays of course I use DDS chips instead of VFOs, so that problem
has been solved<
Has it?
I mean, the problem of frequency stability! Spectral purity is another
matter. But DDS chips have been improving a lot in this area, and are
already good enough for many uses.
> unless all the spur and noise powers summed in a 1 MHz
bandwidth are at least - IN THAT 1MHZ- average -110dBc/Hz - from
100Hz away from the frequency. You don't meet the requirements ot the
Radio Regulations.
I'm not even aware of those Radio Regulations. I suppose you mean the
British ones? In my country they aren't valid anyway - and I wish there
were any at all! What I do is looking at the spectral display, watching
both the noise level and the individual strong spurs. As long as I get
better than 70dB between the carrier and any specific spur, I consider
that good enough for general use. Only for specific applications it
makes sense to strive for much cleaner signals.
I have been using the AD9951 in some projects. In receivers that aren't
critical, I'm actually using it in the worst possible way: Internal
oscillator, with a 20MHz computer crystal, and internal x20 clock
multiplier! Even that is still good enough for many uses, such as my 15
band World Receiver for the AM shortwave broadcast bands. It works great
and is a pleasure to use. For more critical use, that same chip delivers
far better performance when using an external 400MHz clock.
Lots of modern ham transceivers made by the famous brands are using even
much more modest DDS chips than this one, to directly generate several
internal oscillators. So it can't be that difficult to meet applicable
regulations with them!
And I know of no factory made transceiver, for hams or others, made in
the last quarter century, that uses a real VFO! Even if the front panel
buttons are still labeled "VFO A/B", and the like!
Manfred
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