Talk:Crystal radio
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Contents |
[edit] sections
Will add a How-to section in the next few days.
- Should you combine it with the Construction section?
[edit] Move to Crystal Radio
It appears awkward to call this article Crystal Radio Receiver instead of the normal term of reference of Crystal Radio. I propose we move it to Crystal Radio and redirect Crystal Radio Receiver to it just in case anyone ever searches for the "Receiver" version.
John 15:22, 17 November 2006 (UTC)
- I've removed this request from the WP:RM backlog, as it appears to have been done with no opposition. Andrewa 18:09, 14 December 2006 (UTC)
[edit] Lead Section
The lead section is confusing, especially to laymen, I would like to omit jargon like "LC". Many simple crystal radios do not even use variable capacitors for tuning. Crystal radios use a variety of circuits and to present one circuit as defining could be misleading; the lead section should be more generic and inclusive of all that is crystal radio. It is also somewhat wrong in presenting "LC" tuning as the simpliest because inductor-only tuning is simplier than the "LC" tuning. If no one objects I plan to offer an improved, simplier, jargon-free more technically accurate, and more aware lead section wording. -DONE
John 06:14, 12 November 2006 (UTC)
That is a beautifully built artistic radio by VE6AB but in my opinion it is not as representative of crystal radio as an old one. Also, I am concerned that it is a bit commercial because it is offered for sale too. I propose to substitute a photo of a simple-minded, strictly functional old one-slider radio with an open cat whisker detector if I can find one.
John 15:19, 17 November 2006 (UTC)
Why is this awkwardly called Crystal Radio Receiver instead of the normal term of reference of Crystal Radio? I propose we move it to Crystal Radio and redirect Crystal Radio Receiver to it just in case anyone ever searches for the "Receiver" version.
John 15:22, 17 November 2006 (UTC)
[edit] How it works
Added a simple-minded explanation of how it works. Although I have posted a similar explanation elsewhere, I am the original author and I have the right to post it here and hereby declare that I release all copywright to it.
John 15:58, 17 November 2006 (UTC)
[edit] Crystal Connections is closed
The page referenced by "Crystal Connections" is closed. We could remove it, or leave it in until web rot gives us a 404 not found.
- Removed--Light current 09:35, 18 July 2006 (UTC)
[edit] CONSTRUCTION circuit diagram looks wrong
The capacitor should be BEFORE the detector so that it forms a resonant (tank) circuit with the coil. The circuit diagram shows the capacitor after the detector: I'm sure this is wrong.
- I think its wrong too! If its not fixed shortly, I will remove this misleading diagram--Light current 09:50, 18 July 2006 (UTC)
-
- (original commenter) I've been looking at other crystal set designs on the midnightscience.com site and the classic 'Oat Box Radio' apparently uses this circuit with the phones across the capacitor (see http://www.midnightscience.com/project.html). Maybe I'm missing the point, perhaps the coil tunes through parasitic capacitance or something. But I still think it looks wrong, or at least misleading.
The design shown is correct! It is the classic "Fox hole" radio. The coil tunes using a slider connection and resonates against the capacitance of the antenna. This design was used because Variable Caps were not available to the builders (eg soldiers in trenches).
To put it another way, the capacitance of a long wire antena is quite large. This capacitance will swamp a normal tuned circuit and will prevent the tuning cap covering the band. At the very least the antenna needs to be tapped well down the coil or coupled in via a small value cap in series. The solution to all this was to delete the tuning cap, and instead adjust the number of turns in the coil (as shown correctly in the diagram).
BTW, the small cap shown is to bypass the RF after the detector. It is not really necessary.
The capacitor symbol is wrong (should have only two bars), but again, it attempts to show a "homemade" cap (perhaps made from layers of tinfoil from a bubblegum wrapper).
The mention of "ultra-thin litz wire inductors" is clumsy. It should be something like "many thin strands". Also Litz is NOT a new idea. It is very old.
The reference to the Pixie-2 is wrong. It's receiver is NOT a crystal set, it is a "Direct Conversion" set using an "Active Mixer".
The reference also seems to confuse Crystal Oscillators with Crystal detectors. These are two very different things.
[edit] Focus of CONSTRUCTION Section
This section seems to lack focus. Is the title of this section appropriate? It does not seem to address how to construct a 'crystal radio'. Is it intended to address the components that make it up? How they are connected? How it works or what? I think it would be helpful to figure out what this section is doing, do it and name it appropriately.
John 15:33, 17 November 2006 (UTC)
[edit] Diagram removed for clarity
Never mind that the circuit was correct, especially for a very early set. It was also the circuit of the famous Boy Scouts "slider coil" radio.
Have a look at the photo at the top right of the page. Can you see a tuning capacitor? For "clarity" you should remove that photo as well.
And by the way, it isn't a photo of a "modern set", its a re-creation of a very old set, from before the days when tuning capacitors were readily available.
This diagram?
What is confusing about it?
69.76.192.205 20:06, 24 December 2006 (UTC)
[edit] Espionage
It has been suggested that crystal radios may still be in use by spies. This may be because crystal sets have no local oscillator so a counter-espionage organisation cannot determine that any receiver is being used by picking up the local oscillator frequency. This is a bit silly since various categories of receivers have no oscillators (e.g. TRF, Regen) and their much higher performance would be greatly prefered over a crystal set. by --Light current 00:34, 8 September 2006 (UTC)
- a TRF doesn't have a local oscilator but it does have quite a bit of RF amplification which may be able to be spotted, i'm not too familiar with regen so i can't say if that would be simliar. Plugwash 20:02, 20 November 2006 (UTC)
[edit] Transistors in diode detection
The following section has been twice removed from the article, however the reasons of removing seem not convincible for the contributor: The diode detector is not effective, as for weak signals (that must be rectified) the forward and reverse conductivity of the diode differs much less than it would differ for the stronger current. For the signal lever is between 20 - 100 mV, the transmission coefficient of the diode detector varies from 0.12 till as low as 0.01 [1]. The alternative methods of detection using transistors are also known. In the simpliest case, the base and emitter of the pnp bipolar transistor are connected together, and to the radio signal source. The detected radio signal is taken from collector. The transistor, connected this way can be up till 6 times more effective than diode.
Radio was the leading amateur journal in the Soviet Union and should count as a reliable source. Also, from the characteristic of the semiconductor diode in Wikipedia it is also self evident that forward and reverse conductivity does not differ much for the weak signals. Audriusa 15:36, 27 January 2007 (UTC)
It is true that a diode is an inefficient detector for weak signals (it operates in the Square Law mode). However the connection as described simply does not work. Shorting the base and emitter of a transistor produces a normal diode at the collector junction. Gutta Percha
- I removed the above referenced part one of those times mostly because it was hard to understand because of grammatical and technical problems, which were subsequently improved. It is still a little flaky, however, wouldn't you agree a B-E junction of some transistors have a very sharp (non-square law) avalanche in reverse bias (ie. needs a battery!) mode, which can sometimes be more efficient than unbiased detection. John 06:47, 27 February 2007 (UTC)
