[Amps] 160M PI network Toroidal Coil

[Manfred Mornhinweg]

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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