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Crystal radios.
12-07-2016, 05:54 AM (This post was last modified: 12-07-2016 06:14 AM by Janus.)
Post: #1
Crystal radios.
I will put this here as it is relevant to electronics & so called voices or noise.
The old Cats Whisker radios, also known as Crystal radios or Trench radios. Do not need a battery or complicated electronics to work.
And many items, even toys could in the right circumstances work as crystal radios.
The simplest radio & one that needs the strongest signal is just a diode & something to act as a speaker. But a noise could be made from anything that will vibrate.
To improve this add an antenna. Say some wiring, a circuit board or similar.
Add a capacitor & it will tune from station to station & most circuit boards have capacitors of differencing values.
It is far from uncommon for a speaker to make noises or even carry voices, muffled or clear depending upon the mode of transmission, of the source.
A speaker is almost identical to a microphone & if you doubt that, plug a speaker into a microphone socket & record something. So a microphone adding sounds to a recording you did not hear is hardly surprising.
Take a look at the following.

http://bizarrelabs.com/crystal.htm

Or this on so called Trench or Foxhole radios.
https://en.wikipedia.org/wiki/Foxhole_radio

http://bizarrelabs.com/foxhole.htm

As you can see no electronic components needed at all just a Razor blade which vibrates.

The following is a transcript of a interview with Lieutenant Colonel R G Wells about the radio used by British POW's in a Japanese camp.

http://www.far-eastern-heroes.org.uk/Con...g_a_Radio/

A receiver was made using a piece of Coke as the Crystal by the POW's in Colditz.

Modern electronic equipment is built down to a price & is often badly designed, so breakthrough from transmitters is not only common, but expected. Add to that the above & you will see how easy it is, switched on or off. With or without power. To hear what you did not expect to hear.





The following is taken from a leaflet produced by the Radio Society of Great Britain. It is designed to help & advise Radio Amateurs (Hams if you prefer.)

Source..http://rsgb.org/main/files/2012/11/EMC10-final.pdf


Quote:A fairly common problem in amateur radio is interference caused by the fundamental transmission getting into nearby electronic equipment. The term 'breakthrough' is normally used to describe this phenomenon; emphasising the fact that it is really a shortcoming on the part of the equipment being interfered with, and not a transmitter fault.

Quote:The main object of good radio housekeeping is to minimise breakthrough, by making sure that as little as possible of the precious RF energy find
s its way into neighbouring TVs, videos, telephones, and the multitude of electronic gadgets which are part and parcel of the modern home.
In some cases it might be argued that the immunity of the domestic equipment is inadequate, but this does not absolve the amateur from the responsibility of keeping his/her RF under reasonable control. Many of the features which contribute to minimising breakthrough also help in reducing
received interference, so that the virtue of good neighbourliness has the bonus of better all-round station performance.

Quote:Not all modes are equally “EMC friendly” and it is worth looking at some of the more frequently used modes from this point of view.
SSB is one of the least EMC-friendly, particularly where audio breakthrough is concerned.

FM is an EMC-friendly mode, mainly because in most cases the susceptible equipment sees only a constant carrier turned on and off every minute of so.

CW is the old faithful for those with EMC problems, because it has two big advantages. First, providing the keying waveform is well shaped, with rise and fall times of about 10ms or so, the rectified carrier is not such a problem to audio equipment as SSB. The second is that it is possible to
use lower power for a given contact. Of course, low-power CW is not everybody's favourite mode but it does provide a way of staying on the air, even in the most difficult circumstances.

Data modes are more EMC-friendly than SSB. Amateurs who live in locations where running high power is impractical might consider PSK31. This is a mode in which the transceiver is driven from a PC and sound card. It easy to use, and rivals CW in its ability to get through with minimum power.



EMC. All electronic equipment should be built to a design which makes it less likely to either interfere or be interfered with.
This is called ElectroMagnetic Compatability. EMC & standards vary from country to country. But there are standards & equipment should meet it, but often the equipment that is sent for testing is not the same as sold to customers. Thus problems occur.

https://en.wikipedia.org/wiki/Electromag...patibility

EMI is ElectroMagnetic Interference.

https://en.wikipedia.org/wiki/Electromag...terference

The Following Radio Society of Great Britain leaflet aimed at radio amateurs. But also very applicable to anyone getting interference on something like a tape recorder or getting responses on a EMF meter.

http://rsgb.org/main/files/2012/11/EMC04-Final.pdf

If it can interfere with a amateur radio receiver than it can interfere with a cheaply made audio recorder & cause a EMF meter to react.

We all believe in something greater than ourselves. Even if it's just the blind forces of chance. Ambassador G'Kar.
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12-07-2016, 09:32 AM
Post: #2
RE: Crystal radios.
I'd like to add to this commentary. In the past interference was kept to a minimum by housing electronic equipment in a metal case. In more recent years the trend toward miniature, lightweight equipment has pushed the electronics industry to use molded plastic cases. These sometimes had a sprayed on conductive coating to minimize interference, but the coating is often so thin that it can be scratched or flake off in manufacture or ordinary use. Items like cell phones, electronic pads, and computers flood a room with RF interference.

-DFB

Subject: I have a black cat.
Believer: Black cats are bad luck.
Non-believer: It's just a cat.
Crackpot: Black cats are part of the New World Order government conspiracy.
Skeptic: I can test if black cats are more or less lucky than another cat.
Cynic: You only have a black cat to gain power and prestige.

https://www.youtube.com/watch?v=t9iIf4tFoyE
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