Re: NEC-LIST: CFA in short

Paul Moody <paulmoody_at_onaustralia.com.au> wrote:
> Resonance is a means to an end.

I agree. Resonance, per se, is unrelated to radiation. Oscillating
charge, in other words alternating current, is what radiates. Of
course oscillation is easier to excite at resonance. Resonance in an
antenna may be regarded as a way of impedance-matching the
transmission line (source) to the load (radiation resistance). So is
a lumped-element matching network. However, lumped elements tend to
be much lossier than distributed elements.

> ...As far as radiation of EM goes you only have to look to the sky
> above ... there are plenty of EM sources in the galaxy that radiate
> across the full EM spectrum ... as far as I know there is no
> 'antenna' involved at all ... so how does this radiation / power
> conversion occur[?]

Again, it's oscillating charge: moving, charged particles (mainly
electrons) following trajectories that curl around ambient B-field
lines. The trajectory curls due to the normal magnetic force, -e v
cross B. You're right, there's no antenna in the usual sense, of an
artificial structure. Just a _lot_ of charge in a _lot_ of space
(many, many, many wavelengths).

This is a nonthermal mechanism. Any warm lossy medium also radiates
just because of the random Brownian motion of the electrons (etc.) in
it. If the radiator is so lossy that it's opaque, you call it a
"blackbody". The spectrum of its radiation is determined entirely by
its temperature.

All of the brighter astronomical radio sources are nonthermal. Among
them are recombination emission, cosmic masers, pulsars, quasars,....
To be as bright as a typical pulsar, for example, a blackbody would
need to have a temperature of the order of 10**18 K, IIRC.

Beyond the scope of the NEC-LIST, I'm afraid.

  -Chuck W1HIS
Received on Sun Feb 28 1999 - 04:33:05 EST