What's the lowest radio frequency one could usefully transmit phone quality speech/music upon? I am ashamed to admit I have entirely forgotten what little wireless theory I knew.
Note his point about longwave, then glance at the whopping antennas as you drive past Droitwich on the M5.
Anything lower than mediumwave and you'll need an antenna the size of... well, bigger than any land area you or any of your friends can afford (regardless of whether you mount horizontal or vertical - it still has to have guy ropes, and probably air traffic clearance at that height).
Mediumwave antennas will comfortably fit inside a field or on a ship. Hence why there are pirate mediumwave stations but not longwave stations. Sunshine Radio out of Ludlow operated an AM-MW TX from a field (and briefly from a raft in a lake, if anecdotes are to be believed), before they went legal and rented a proper TX off of Merlin like all the other ILR sell-outs.
Radio 4's wavelength is about one and a half kilometres, for example. It only gets longer as the frequency gets lower. The rough equation is "divide 300,000 by KHz to get metres", although I'm sure a physics student will be along in a moment to talk about the speed of light etc.
Well, I don't have any qualifications in physics but I do have a HNC in electronics, specialising in communications.
I can't actually remember anything as I've been doing software since I graduated, but I one thing I specifcally don't remember is any fudge factor for variance in the speed of light in wavelength calculations; the speed of propogation though air was assumed to be constant (at ground level).
(insert hazy memory may be talking bollocks disclaimer here)
The only problem I remember re variance in the speed of light was the fact that different frequencies propogate at different speeds[1]. Fourier shows us that a complex waveform is in fact made up of many sine waves of different frequencies. If all these frequencies are travelling at different speeds when it gets to the other end your waveform is going to be right mullered
( ... )
Mediumwave antennas will comfortably fit inside a field or on a ship
That's pushing it for "comfortably". Looking at pictures of the MV Mi Amigo with that vast top-heavy tower mast on top of it, I was always happy to be sitting in a tower block. It was easier for the Buzbies to show up outside, but at least Cantril Farm never threatened to capsize.
Ah, yes, but the Mi Amigo (and MV Communicator etc) had the antenna mounted vertically, instead of slung horizontally between two masts. Capital Radio (Holland) and Radio 270 had a horizonally slung antenna and fared much better in storms (although Capital Holland slipped her anchor for an entirely different reason - debts and lack of maintennance).
There's a very reasonable chance that I have this wrong, but I was vaguely aware that phone quality audio was typically considered 8khz sampling rate - which would tie to the 4khz you mention, because Nyquist theory says you need to have twice the transmission frequency of the highest audible frequency you want to represent, so that you can get a peak and a trough in.
I think.
No idea if that applies to transmission via radio waves, but if so, it would mean that there's a x2 on top of that 40khz.
I suspect you're right. Still well within the cricket ground (I am English and we'll have no 'ballpark' malarkey here) and aiming to wallop the pill into the beer-tent.
IIRC: Long-wave went down to about 150kHz.
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Anything lower than mediumwave and you'll need an antenna the size of... well, bigger than any land area you or any of your friends can afford (regardless of whether you mount horizontal or vertical - it still has to have guy ropes, and probably air traffic clearance at that height).
Mediumwave antennas will comfortably fit inside a field or on a ship. Hence why there are pirate mediumwave stations but not longwave stations. Sunshine Radio out of Ludlow operated an AM-MW TX from a field (and briefly from a raft in a lake, if anecdotes are to be believed), before they went legal and rented a proper TX off of Merlin like all the other ILR sell-outs.
Radio 4's wavelength is about one and a half kilometres, for example. It only gets longer as the frequency gets lower. The rough equation is "divide 300,000 by KHz to get metres", although I'm sure a physics student will be along in a moment to talk about the speed of light etc.
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I can't actually remember anything as I've been doing software since I graduated, but I one thing I specifcally don't remember is any fudge factor for variance in the speed of light in wavelength calculations; the speed of propogation though air was assumed to be constant (at ground level).
(insert hazy memory may be talking bollocks disclaimer here)
The only problem I remember re variance in the speed of light was the fact that different frequencies propogate at different speeds[1]. Fourier shows us that a complex waveform is in fact made up of many sine waves of different frequencies. If all these frequencies are travelling at different speeds when it gets to the other end your waveform is going to be right mullered ( ... )
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That's pushing it for "comfortably". Looking at pictures of the MV Mi Amigo with that vast top-heavy tower mast on top of it, I was always happy to be sitting in a tower block. It was easier for the Buzbies to show up outside, but at least Cantril Farm never threatened to capsize.
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Actually, many odd corners of the wireless spectrum are oddly interesting. Has anyone tried using the output of numbers stations for the lottery?
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Folk song, bicycles and number stations, expressed as hand-crafted steel.
I've got the previous incarnation, Il Pompino (italian for hand-job) and it's resonant at 11Mhz.
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I think.
No idea if that applies to transmission via radio waves, but if so, it would mean that there's a x2 on top of that 40khz.
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Whoa. When did this happen?
I'm always the last to know.
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No you're not, you pasty-eating piskie. You can take your leather-on-willow ways back to Kernow with you.
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