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childhood inventions
In article , Max
Demian scribeth thus On 24/02/2018 08:57, Brian Gaff wrote: Yes when I was young I did a similar thing. It actually worked point to point using alantern torch, but the bias was through a class a run big power transistor. Very wasteful of course. if you modulated it too much though you ended up with some weird kind of contrast expansion distortion. There was a project in Radio constructor back many years ago using mains filament lamps mounted on a high post. that did use transformers but also had to derive 200 volts of DC as well which was quite a mean feat and the amp required for the audio had inverse distortion to compensate for the non linearity of the bulbs. The audio was receive in a similar way to described, however Ithink you mean convex lenses. I used some plastic ells cheapo kids telescopes. I did once try to send audio wirelessly with electrodes buried in the ground, similar to the (telegraphic?) communication used in WW1. It only reached a few feet and there was lots of mains hum: +------ ------+ | | | | Transmitter Receiver | | | | +------ ------+ Did just that when i was a nipper worked quite well over around a hundred yards or so and no maims 'um;!... Need to set the earth electrodes a decent distance apart.. -- Tony Sayer |
childhood inventions
On Tue, 27 Feb 2018 23:10:19 +0000, tony sayer wrote:
In article , Max Demian scribeth thus On 24/02/2018 08:57, Brian Gaff wrote: Yes when I was young I did a similar thing. It actually worked point to point using alantern torch, but the bias was through a class a run big power transistor. Very wasteful of course. if you modulated it too much though you ended up with some weird kind of contrast expansion distortion. There was a project in Radio constructor back many years ago using mains filament lamps mounted on a high post. that did use transformers but also had to derive 200 volts of DC as well which was quite a mean feat and the amp required for the audio had inverse distortion to compensate for the non linearity of the bulbs. The audio was receive in a similar way to described, however Ithink you mean convex lenses. I used some plastic ells cheapo kids telescopes. I did once try to send audio wirelessly with electrodes buried in the ground, similar to the (telegraphic?) communication used in WW1. It only reached a few feet and there was lots of mains hum: +------ ------+ | | | | Transmitter Receiver | | | | +------ ------+ Did just that when i was a nipper worked quite well over around a hundred yards or so and no maims 'um;!... Need to set the earth electrodes a decent distance apart.. Unlike wireless communication, the attenuation rate (like wired and fibred links) is a constant dB per unit distance similar to an analogue fader in a sound studio mixing desk. Assuming, for the chosen electrode separation, your "Earth-link" had a loss of 100dB over that 100 yds range, each additional yard of range would add another dB of attenuation. Doubling the range would add another 100dB (possibly even more) unlike the case of a wireless link where doubling the range increases the attenuation by a mere 6dB for each successive doubling. Like the case of the "Light Phone", it's just another 'interesting experiment' to prove the limitations of such novel means of communication. That's not to say either technique is completely useless, more a case of being rather limited in their application. -- Johnny B Good |
childhood inventions
On 01/03/2018 13:09, Terry Casey wrote:
In article , says... I did once try to send audio wirelessly with electrodes buried in the ground, similar to the (telegraphic?) communication used in WW1. It only reached a few feet and there was lots of mains hum: My brother and I tried this over 50 years ago and it worked quite well, considering the rather crude set up. The transmitter end was quite good - a Mullard 5-10 connected to the water main which din't encounter the earth proper until it got to the other end of the house and an old chassis buried at the far end of the back garden, so a fair distance between them. The receiver was crude beyond belief - a pair of longish wires connected across the volume control of a transistor radio with crocodile clips on the ends! The problem was finding suitable areas of earth to use as reception sites - back alleys, mainly, but did work our way down to a road that had grass verges each side - which made it much easier to insert our probes - meat skewers! - than the compacted earth of the alleyways. However, whereas before our probes were in a parallel plane to those of the transmitter, we were now going sideways and reception started to drop off rather rapidly (and the hum increased!). I can't honestly remember how far we got all that time ago but it was several hundred yards. Of course, had the water main gone straight down, it would have reduced the distance between transmission probes to half, or possibly less. Were these (and Tony Sayer's) experiments prompted by a Practical/Wireless/World type article? My idea came from a (first world) wartime magazine called Amateur Mechanic (of which we had two (properly bound) volumes), covering everything from how locks work to how to stuff (taxidermically) a cow). DIY before the term was invented/popularised. It was in an article about "wireless" communications, which made the distinction between "wireless" and "radio", the latter illustrated by instructions how to make a crystal set to receive ultra long wave Morse communications from ships. This was before wireless telephony, whether radio or ground. -- Max Demian |
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