On Thu, 10 Feb 2005 22:19:47 +0000 (GMT), "Dave Plowman (News)"
wrote:

Quite, all stuff I learnt well over 30 years ago. So why do you say I
was only "partially" correct? Which part do you believe I got wrong?
A "ferrite rod aerial" describes the ferrite *and* the coil BTW.

Ferrite rod aerials are irrelevant to UHF. Or even HF, if you look at the
average radio which includes SW.

I have seen many radios with ferrite aerials for shortwave. I was
however only addressing the erroneous point made by a poster that the
size of an aerial is always proportional to the wavelength.

You might also think about other things that are capable of
concentrating the received field.

No - I think you should explain how the device in question might work?

I have no idea whether the device in question works or not, and if it
does work what principle it adopts. It probably *is* a scam. I
recall an "automatic tuner" that lots of hams were conned into buying
years ago, and which was advertised in some reputable ham radio
magazines.

I am not defending the aerial at all. I just get a tad annoyed when
people make statements that something that is claimed is totally
impossible when it would be trivial to prove one way or the other. So
I'm just picking holes in the reasoning of people that are saying so.

I will not make the statement that the aerial in question is
*impossible*. It is not as if it would violate any basic principle of
physics. Maybe it is similar to a ferrite aerial. At UHF you could
not make a conventional ferrite aerial with a coil & capacitor,
because any coil would have far too much inductance to be able to make
it resonate at UHF. But maybe something like a stripline resonant
circuit on a ferrite base? Or some other material that can
concentrate the magnetic or electrical component of the EM field.
Maybe I'll get curious enough to waste the price of the aerial to find
out for sure that it is a scam. I agree that the claims sound very
suspect, especially the one regarding ghosting (though a ferrite
aerial has very pronounced null regions that would be useful to
eliminate ghosting).

*If* there is such a principle behind the aerial, it would not be
something the mobile phone bods would be clamouring over. Because, as
I am sure you are aware, a ferrite aerial can only be used for
reception, not transmission. An aerial for transmission must couple
both E and M fields, and ferrite acts only on the M field.

--
Cynic