[Amps] 160M PI network Toroidal Coil

[Manfred Mornhinweg]

Peter, and all,

> Actually Manfred, your government has signed up to them! I'm
> referring to the International Radio Regulations, published by the
> ITU, and signed up to, by all the participants in a World Radio
> Conference. Is there not a ban on spark transmitters? That's in the
> RR.

I see!  What I don't see, is how that would be actually applied in 
Chile. It's almost impossible for the layman (that is, non-lawyer) to 
wok his way through the laws here. Typically a law will make reference 
to dozens of previous laws, to norms, standards, and when you try to 
look them up, they can't be found! Or those that can be found, in turn 
refer you to yet other laws and rules, that cannot be found. Often the 
formulations in the laws are very general, like "the allowable 
modulation modes will be those defined in the respective standards", but 
nothings tells which standards are meant, and where to find them. Very 
often they haven't been defined at the time a law is made, and the law 
can exist but be inapplicable because for many years the standards 
aren't written down!

The fact is that in Chile anyone can import any radio, and at least on 
the ham bands he can use it without requiring any type approval. There 
is essentially no enforcement of anything on the ham bands. On 
commercial bands I understand that radios must be type-approved, in 
principle, but in practice I know of many people using very low quality 
radios, directly imported via eBay from you-know-where, on commercial 
frequencies. I seriously doubt that these are able to comply with the 
ITU standards.

The current ham regulations here do say that they will be applied 
according to all international treaties and agreements signed by Chile, 
but gives no additional detail. Nor does it hint at any technical 
standards for equipment quality.

So, in principle ITU standards are fully valid here, but in practice 
almost nobody knows them, and so, let's say it this way, their 
application is entirely voluntary in practice.

It would be very bizarre indeed if an inspector sent by the government 
showed up at the home of a ham, to fine him because the local oscillator 
in his radio doesn't meet ITU specs!

> Interesting point about iron cores and VFOs. As I recall, the old
> Command transmitters were very stable, and they had iron cores in
> both the VFO and the PA. But they were magnetically loosely coupled,
> unlike toroids.

At least the thermal coefficient of certain magnetic materials is well 
known and reproducible. So, it's possible to largely compensate for it, 
in a well done design. But this tends to be complex. For example, 
compensating for thermal effects in a slug tuned coil depends on how far 
the slug has been inserted. That requires adjustable compensation, and 
almost endless fiddling in the lab. It's much better to make VFOs using 
large size coils on stable formers, without a magnetic core, polystyrene 
capacitors, air variable capacitors, with a good circuit design (such as 
Clapp oscillators using JFETs) and then compensate for the small thermal 
coefficient that remains. Indeed the output of a good VFO is spectrally 
cleaner than that of even the best DDS, because the latter does have 
spurs. But the phase noise of a DDS is better, its stability is much 
better, and it can produce frequencies from zero to some maximum, at 
constant amplitude. All that without requiring any adjustment, and under 
very simple microprocessor control. And it can instantly jump to any 
other frequency, and, and, and...

Tom,

I had a look at the SI570. Looks interesting! Certainly not for every 
application, but as a local oscillator for simple radios, it does look 
attractive. I will eventually buy a few to play with them. What I like 
least is the relatively complex calculation necessary to control it. I 
usually employ PICs in my projects, and the typical PIC with its 16 bit 
integer math makes such calculations quite cumbersome and slow. It's OK 
for occasional frequency changing. But flipping around a tuning knob at 
a rate of perhaps 1000 steps per second, but certainly overtax the poor 
PIC and make it get out of step!

Manfred


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