Valotonin wrote:I really wanted to know what kind of frequency bands that antenna is intended for and whether it is for audio or audiovisual reception. If anyone with an inclination towards that kind of tech knows, I would much appreciate it.
I've seen one or two around the London area and haven't been able to find much on them which is why. I may have even seen the one in Nick's avatar at some point.
Is it just a much more comprehensive receiver for television or would the owner be a shortwave radio enthusiast or the like? I know that someone here knows haha.
It's a "cobweb" dipole antenna. Dipoles are the simplest types of antenna, basically a piece of wire that's half the maximum wavelength. Wavelength is the reciprocal of frequency, multiplied by the wave speed (which for practical purposes is the speed of light for electromagnetic waves through air).
The shape of the dipole doesn't matter as much as its length, which tunes it to the frequency band in question. The cobweb setups usually have 3 or more separate dipoles (so they can support multiple bands) arranged in concentric square or U shapes. The exact frequency bands depend on the length of the dipoles, but are usually in the megahertz to low tens of MHz range, and for amateur radio, the allowed and commonly used bands are 14, 18, 21, 24 and 28 MHz - corresponding to dipole lengths of about 10m down to 5m.
Amateur operators are only allowed to broadcast on certain frequency bands, but for the number stations, obviously government and military operated, other frequencies were used. So those antennas would be probably be precisely tuned to those frequencies for maximum energy efficiency, resulting in a completely bespoke setup like the one you see on the Cornet Project cover.
The frequency bands are split up into sub-bands and sometimes sub-sub-bands and eventually channels, each +/- around a centre frequency. The bandwidth of these channels depends on the modulation and encoding used but generally they'd be less than 10kHz. You wouldn't get video at those bandwidths (remember how slow your 14.4k modem was?) So I'd guess and say the antennas you see around town are amateur radio operators broadcasting and receiving audio, morse code and encoded images.
In summary: 5-10m shortwave antennas, 28-14MHz bands, 5-10kHz channels, audio.