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
========================
Visit my hobby homepage!
http://ludens.cl
========================
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|