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I object to the use of the perjorative "Naive" in regards to the simple circuit presented. It implies a preference or judgement that has no place in an encyclopedic article.
For example, getting 8-year-olds to build a working radio in less than an hour requires some simplification, and the the circuit presented does that. Perfect for the application.
Thbusch ( talk) 16:53, 27 August 2009 (UTC)
2 of the first 3 links are broken, 1 to the 'enthusiasts', the other to using modern components
for 'hi' performance.
Just after I added some text to the cites too! ADVICE always check a link works before trying to 'improve'it!
Dug out a few links that may be relevant. Some are obviously commercial sites, for those who are interested.
-- 220.101.28.25 ( talk) 09:28, 6 December 2009 (UTC)
This is a new link featuring an improved powered crystal set using a few devices. It also provides a simulation file for those interested in understanding how each part of the circuit works: https://jademann4.wixsite.com/crystalset-perfected — Preceding unsigned comment added by 2600:8800:1701:AFD0:85AB:FD58:977B:C003 ( talk) 11:26, 4 March 2023 (UTC)
Added subsections under 'How it works' describing the different parts of a crystal set, addressing some of the topics discussed on this page, such as impedance matching and selectivity. -- Chetvorno TALK 06:40, 12 July 2010 (UTC)
This edit war on the article needs to stop. Discuss the matter here with regard to Wikipedia's policies and guidelines, then change the article in accordance with compromise and consensus. Discuss the reliability of the sources and the representation of the cited sources in the article text and diagrams, not each other's intelligence, abilities or personal views. Having said that, here is my input: First, the scan of the 1950s article by L.B. Robbins looks authentic to me. Does anyone have any evidence that it is a modern con with technical errors introduced by someone else? If not then it seems to be a WP:RS reliable source and may be used to support the article. Second, I have made that circuit and so I know it works. This is WP:OR and so cannot be used in the article, but should be enough to stop the bickering. (I was trying to re-create a crystal radio made by my grandfather during WW2 and so wound a coil like his on a wooden former, but used a schottky diode as a detector and an audio amplifier instead of Hi-Z headphones. My grandfather's design was capacitor-less with a sliding earth-tap on the coil, connected by sandpapering away some insulation lacquer after winding it. Adding a small trimmer capacitor increased the selectivity and 'peaked' the reception slightly, but still only the most local medium-wave station was really receivable). So, the circuit is authentic, and it works. What's the problem with mentioning it in this article? -- Nigelj ( talk) 08:29, 20 August 2010 (UTC)
P.S. A completely different inductance is needed with the capacitor compared to without it, for the same long wire antenna and same reception band. I can dig out my old experiments and count the turns if anyone's interested, but it's largely irrelevant as it's WP:OR, however it shows the principle is sound. -- Nigelj ( talk) 08:37, 20 August 2010 (UTC)
Several of the diagrams have a second capacitor labeled C2, on the headphone side of the diode. Given that the current on that side of the diode must be DC (albeit pulsating), what does C2 do? Mcswell ( talk) 04:25, 28 February 2021 (UTC)
I notice that, in addition to deleting the image, all mention of capacitance has been removed from the "Tuned circuit" bullet point at the top of the 'How it works' section. This is grossly false, and misleading to nontechnical readers, since it defines a tuned circuit as an inductor alone: "[A tuned circuit] . . . consists of a coil of wire called an inductor or tuning coil used to tune in different stations." Helllowwwww???? As the text made clear before it was eviscerated, a tuned circuit in a crystal radio always consists of an inductor and a capacitance, but some circuits use the capacitance of the antenna. The original description was thoroughly sourced. I don't want to be accused of continuing the above edit war, but unless somebody comes up with a compelling reason this dreck should stay, I'm changing it back. -- Chetvorno TALK 22:24, 20 August 2010 (UTC)
The slider in the illustration is on the right, not the left. —Preceding unsigned comment added by 68.42.44.186 ( talk) 13:22, 18 July 2010 (UTC)
The explanation of how the crystal detector is wrong. I have made several attempts to correct (perhaps not very well) but my edit is simply removed. There does not seem to be any point in correcting errors if the corrections are simply removed and the incorrect explanation retained.
david.tucker2@virgin.net Davidpetertucker ( talk) 17:09, 30 January 2011 (UTC)
Crystal detector
This explanation would only work is the signal measured several volts peak to peak.
Since the signal in only micro volts p-p how can a diode possibly rectify such a signal?
The real explanation relies on the fact that the diode is a nonlinier conductor and this mices the sidebands and carrier frequencies resulting in the recovery of the modulating frequency (among others). The purpose of the bias is to move the opperating point to the part of the diode's curve which maximises the amptitude of the desired signal.
— Preceding unsigned comment added by Davidpetertucker ( talk • contribs) 09:55, 2 February 2011 (UTC)
The latest revision is better because it avoids the false myth of "a knee in the diode curve," and is more small signal oriented. A technical explanation of this can take the frequency domain approach of collapsing sidebands, but that is very abstract for many. There is also a very clear time domain explanation that requires a very clear understanding of detection. 128.49.9.18 ( talk) 17:25, 9 November 2011 (UTC)
"energy of only 10−16 W/cm2"
W/cm2 is a power density NOT energy (which should be Joules). Someone put this right, please. 194.72.120.131 ( talk) 10:23, 11 May 2011 (UTC)
Do we need a section about how to make a radio that is ineffective at tuning? John ( talk) 04:43, 28 June 2011 (UTC)
Was this actually used in the day, or some contributor's original research? I've never seen a book or Web page describing this technique of setting a cat's whisker, and One thing that troubles me is how one is expected to hear anything in the headphones with a buzzer running within arm's reach. --
Wtshymanski (
talk)
22:32, 10 November 2011 (UTC)
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The article describes the impedance of the crystal (piezo) earpiece as being ~ 1 Mohm. This is the DC value. IIRC, the AC impedance is still quite low (~5kOhm), so a coupling transformer is desirable. Have I got this right? I haven't changed the article; someone better informed may wish to. — Preceding unsigned comment added by 87.194.171.29 ( talk) 02:29, 10 August 2012 (UTC)
In order for a radio to work it is necessary to have a ground connection or the radio needs a very large capacitance to act in lieu of the earth.
This requirement is similar to that for a power delivery system. The current from a power plant arrives at your home, it passes through various devices in your home and then travels to the ground wire in the circuit box and from there to a ground wire buried in the earth under your home. In a sense the earth itself is the conductor that returns the current to the power plant where there is a massive grid of conductors buried in the ground. The earth is not a great conductor but there is a lot of it and so it works. There is no wire that returns the current to the power plant. The earth could be replaced with a gigantic capacitor but that would be prohibitively expensive. Similarly, a radio needs either a ground connection or to be connected to a large capacitance that acts like the earth. The use of early crystal radio sets in aircraft and such was problematic due to the vibrations to which the radio was subject not due to grounding problems. I am not certain about the grounding of aircraft but will speculate that the tremendous amount of air through which a moving craft is passing will act like a sufficient ground/capacitance. Zedshort ( talk) 16:16, 12 September 2014 (UTC)
Well, this has been a truly fascinating exchange and collection of factoids. Now, would someone please explain the presence of a ground connection in diagrams of radios without using the circular reference of a counterpoise, and do so in twenty words or less. Thank you. Zedshort ( talk) 14:03, 13 September 2014 (UTC)
I have made a quite serious edit to this section. Given the interest in crystal sets evident in this talk page, it is likely that what I have done will prove to be controversial, so I shall try to explain. Firstly I have corrected the statement of the max power transfer theorem, so that it reads correctly. Impedances should not be equal for max power transfer, but one should be the conjugate of the other. I do not expect any disagreement over this. However, it seems to me that the only respect in which this theorem can be applied to a crystal set is that the impedance of the power source (i.e. the aerial) should be matched to that of the the load (the earphones). Ideally, the equivalent resistance of the tuned circuit at resonance should be severely mismatched to the source impedance of the aerial in order to minimise resistive losses in the tuned circuit, which can only be wasteful. If the tuned circuit were power matched to the aerial, maximum power would be transferred to the resistance of the tuned circuit, which is not what is required. It is for this reason that I have deleted all references to the idea of matching the aerial to the tuned circuit. Transforming the equivalent resistance of the aerial has significance in relation to selectivity, and this concept is best treated separately. Both topics (impedance matching for max power transfer to the headphones, and aerial resistance transformation for improved selectivity) are complicated by the fact that so many different crystal set circuits are used. In the circuit which accompanies the "Impedance Matching" section, it is clear that the left-hand slider can be used for tuning, and the right-hand one for impedance matching, and that the right-hand slider will also affect the Q of the inductor, and therefore the selectivity. In more complicated circuits where a variable capacitor is used for tuning, and the aerial is connected to a variable tap on the inductor, the useful effect of the different tap positions will be to improve selectivity when the tap is low, since then the Q of the parallel tuned circuit will be at its greatest. In this type of circuit, the resistance of the headphones will lower the Q of the parallel tuned circuit, so for greater selectivity, the resistance of the phones should be high. In this circuit, power transfer to the phones will also be affected by the tap position, so that the tap control can be used either to improve selectivity, or to achieve best sensitivity, depending on requirements. g4oep — Preceding unsigned comment added by 77.96.60.31 ( talk) 11:43, 4 January 2015 (UTC) G4oep ( talk)
Hi - I have looked at the paragraph you refer to, and although there is not much there to object to, I feel that the ideas involved in this section could be presented more rigorously. The paragraph starts by stating that the aim is to transfer power to the headphones, then states "Therefore, in better receiver circuits, to match the antenna impedance to the receiver's impedance...". The point that I tried to express in the material you deleted is that the first objective is not necessarily achieved when the second is fulfilled. True, it is necessary to match the receiver's aerial and earth terminals to the actual aerial/earth system in order to maximise power absorbed from the aerial, but then this absorbed power must be transferred to the phones with as little as possible lost in the tuned circuit. The resistive component of the input admittance of the receiver (considered as a parallel equivalent circuit) can be represented by 2 parallel components - 1) the transformed equivalent parallel resistance of the coil (or of the tuned circuit as a whole- Rc)) and 2) the transformed resistance of the phones/detector combination (Rp). For maximum power in the phones, Rc should be large compared with Rp since in a parallel equivalent circuit, the same voltage is applied to both resistors, and P is inversely proportional to R (P = V^2/R). This condition (Rc >> Rp) can be represented by saying that the antenna should be matched to the phones, and mismatched to the resistance of the inductor. That was what I wrote, and I feel that it should not have been deleted without proper justification. The resistances of the coil, and of the phones are indeed separable, and the design and adjustment of the circuit can be altered to control the fraction of the available power which is dissipated in each simply by adjusting their relative magnitudes. These magnitudes are under the control of the various transformation ratios. This idea is completely false: "maximizing power to the earphone also maximizes power lost in the coil". I have altered the text again. I expect that someone will quibble that the points I have made are not referenced, but it should be obvious to anyone who understands ac circuit theory that what I have written is correct; trust me - I am an engineer. If you don't understand circuit theory, don't change it. g4oep.
In the section about "use as a power supply" it states that AM stations modulate only 30 percent. This is only partially true. Aircraft navaid stations modulate their IDs 30% to leave room for voice modulation over the ID. But broadcasting stations routinely modulate 100% and even 125% in the positive direction. Can someone fix this please? 108.244.204.22 ( talk) 01:12, 10 January 2015 (UTC) Chip Veres 1-08-15 ]
Intro page says "By the nature of their operation, crystal radios can only demodulate amplitude modulation (AM) signals, not frequency modulation (FM) or digital signals."
Not true...
Crystal Radios CAN demodulate FM signals very easily. There's a number of HOWTO DIY pages on this.
See: http://scitoys.com/scitoys/scitoys/radio/radio.html#crystal for one example. or http://frank.pocnet.net/other/Sylvania/40_Uses_for_Germanium_Diodes.pdf or http://www.radio-electronics.com/info/rf-technology-design/fm-reception/fm-slope-detector-discriminator.php — Preceding unsigned comment added by 50.185.136.67 ( talk) 03:53, 31 March 2015 (UTC)
I've researched this question and concluded that reception of normal wideband FM is also possible with some crystal sets up to 30km from a transmitter. I've mentioned this fact and a link, but have found many more references during my research. We could probably use some wording to mention some of these as well, like their designs, efficiency, techniques etc. Main discussion of an optimized crystal discriminator design:
Slope detector vs. FM discriminator response curve:
Previous design:
Some others (also referenced above and from other places):
- bkil ( talk) 22:46, 3 July 2020 (UTC)
Recently the description of the crystal detector in the Design section bullet points was changed from:
to:
I think the previous version was better and should be restored. The detector is the most important part of the radio. I think it is important for readers to understand what it does; it demodulates the radio signal, separating the audio modulation from the carrier wave and producing the audio signal which is converted to sound waves by the earphone. The new text, in addition to being repetitive, doesn't make this clear. -- Chetvorno TALK 22:16, 7 May 2016 (UTC)
I might be being dumb and missing something fundamental, but wouldn't substituting the simple diode for four of them in a bridge rectifier provide a signal of twice the strength? After all, the idea for the envelope detection setup is to remove the inverse side of the original wave; if we instead invert it, we get twice as much positive signal. Yes?
Obviously this would be a massive pain to try and implement on an original oxide-coated-conductor and cat's-whisker type radio, but a semiconductor based model could use it... 209.93.196.109 ( talk) 20:14, 9 July 2016 (UTC)
The photo shows a boy wearing what appears to be a modern device of some sort. It is not really informative. Perhaps we can find a photo of an actual crystal radio and its associated circuit diagram. Zedshort ( talk) 13:51, 19 December 2016 (UTC)
From our German colleagues, a homemade set:
Capacitor tuned; up-close-and-personal diode.
Also, a nice crystal:
Glrx ( talk) 20:17, 28 December 2016 (UTC)
I agree that the current lede photo is unsuitable. It shows nothing about the topic and is much later that the important use of such radios, which was before WW II and certainly before transistors. I would suggest File:Kristallradio.JPG. It clearly show the cats whisker detector and the crystal and the headphones. There are several other views of this item as well. Images of modern crystal radios belong in a separate section on later usage.-- agr ( talk) 19:38, 27 July 2018 (UTC)
Assuming the wire of the coil is insulated, how is a sliding contact able to work? ZFT ( talk) 22:35, 20 January 2017 (UTC)
Editor LSMFT has removed all use of the term "cat whisker detector" from this article. I think this should be reverted.
The primitive semiconductor detector used in early crystal sets, which consisted of a fine wire touching a piece of crystal, was called either a "crystal detector" or "cat whisker detector" in literature of the time. The problem is, the semiconductor diode used in modern crystal sets is also sometimes called a "crystal detector", so a different term is needed to unambiguously distinguish the antique detectors. This article, following usage in most modern sources, called it a "cat whisker detector". LSMFT changed these terms to "crystal detector", claiming that 'cat whisker detector' was "not historically accurate"
LSMFT is wrong. In the first place, inventor Greenleaf Whittier Pickard named the device "cat whisker detector" when he invented it. Second, numerous wireless books of the time called it a "cat whisker detector". Third, even if they didn't, numerous modern reliable sources, technical and historical books and websites, call it a "cat whisker detector" (in modern sources the alternate form "cat's whisker detector" is usually used). This is probably the most common term for it today, used to distinguish it from various devices used later in the history of electronics, such as the germanium "crystal detectors" used in radar sets in WW2. Here are sources supporting these points:
-- Chetvorno TALK 21:44, 1 May 2018 (UTC)
Hello, Editor
Chetvorno.
The 14:26 1 May revision of the article did NOT remove all use of the term "cat-whisker detector". It was included, WITH CITATIONS, in the "Crystal detector" section of the article. The term WAS NOT deleted from the article completely.
Please carefully read the 14:26 1 May revision.
Thank you, LSMFT ( talk) 17:39, 2 May 2018 (UTC)
The article has a red link to square law detector. The article on decibel, and especially the case, especially in optics, where detectors give an output voltage proportional to input power, caused me to look for a square-law detector article. Gah4 ( talk) 03:01, 12 January 2019 (UTC)
@ Gah4: The reference is Lee, p.5-6. Bose's detector experiments are described in Sarkar, p.296-297, 482, see also Crystal detector#Bose's experiments. Bose's galena detector consisted of a tiny galena crystal with a point contact, mounted either in a horn antenna or at the focus of a lens, with a DC current from a battery through it. Microwave radiation caused an increase in current through the crystal, which he detected with a galvanometer. The DC forward bias would have moved the operating point up on the diode IV curve, making it unlikely that the junction was functioning as a rectifier. Lee says the current change was due to change in resistance of the crystal due to heating, as in a bolometer. One indication that it was not functioning as a rectifier is that Bose noted the detector also responded to light and ultraviolet. However other sources either aren't aware of or don't make this distinction, and just say Bose invented the first 'semiconductor detector'. -- Chetvorno TALK 00:36, 12 March 2019 (UTC)
Bose did not seek out a patent for this. Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves proving that communication signals can be sent without using wires. He sent and received radio waves over distance but did not believe it to be useful. EyesoftheOperation ( talk) 09:53, 18 October 2019 (UTC)
This article is mostly bogus. It is more or less someone's opinion and not factual. Nikolas tesla 1892 with a type of commercial patent later. Marconi came after Late 1890s- Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves proving that communication signals can be sent without using wires. He never sought to patent anything radio related because he felt they were technically useless. Tesla contributed more in the field of frequency communication with derivatives based on the simple radio oscillator he had put together, than any other inventor at that time. EyesoftheOperation ( talk) 09:52, 18 October 2019 (UTC)
There is no question that the radio signal can be used to power the radio itself, and the answer is yes. Billy Cheung (SP?) from Hong Kong has many youtube videos doing just that. Many are also FM, so yes there are FM crystal radios. Ex: https://www.youtube.com/watch?v=1q1qwCPC5kM There are other youtube videos online of LEDs and even a digital watch being powered. Ex: https://www.youtube.com/watch?v=0WvZC3-mR6Q It's not IF power from the signal can be used, but HOW MUCH. The answer is the amount is small, but usable. — Preceding unsigned comment added by 2001:FB1:C4:7F0:18A5:1040:337F:513A ( talk) 00:21, 31 January 2022 (UTC)
This is the
talk page for discussing improvements to the
Crystal radio article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
Archives: 1 |
![]() | This ![]() It is of interest to the following WikiProjects: | |||||||||||||||||||||||||||
|
![]() | A fact from Crystal radio appeared on Wikipedia's
Main Page in the
Did you know column on 2 April 2004. The text of the entry was as follows:
| ![]() |
I object to the use of the perjorative "Naive" in regards to the simple circuit presented. It implies a preference or judgement that has no place in an encyclopedic article.
For example, getting 8-year-olds to build a working radio in less than an hour requires some simplification, and the the circuit presented does that. Perfect for the application.
Thbusch ( talk) 16:53, 27 August 2009 (UTC)
2 of the first 3 links are broken, 1 to the 'enthusiasts', the other to using modern components
for 'hi' performance.
Just after I added some text to the cites too! ADVICE always check a link works before trying to 'improve'it!
Dug out a few links that may be relevant. Some are obviously commercial sites, for those who are interested.
-- 220.101.28.25 ( talk) 09:28, 6 December 2009 (UTC)
This is a new link featuring an improved powered crystal set using a few devices. It also provides a simulation file for those interested in understanding how each part of the circuit works: https://jademann4.wixsite.com/crystalset-perfected — Preceding unsigned comment added by 2600:8800:1701:AFD0:85AB:FD58:977B:C003 ( talk) 11:26, 4 March 2023 (UTC)
Added subsections under 'How it works' describing the different parts of a crystal set, addressing some of the topics discussed on this page, such as impedance matching and selectivity. -- Chetvorno TALK 06:40, 12 July 2010 (UTC)
This edit war on the article needs to stop. Discuss the matter here with regard to Wikipedia's policies and guidelines, then change the article in accordance with compromise and consensus. Discuss the reliability of the sources and the representation of the cited sources in the article text and diagrams, not each other's intelligence, abilities or personal views. Having said that, here is my input: First, the scan of the 1950s article by L.B. Robbins looks authentic to me. Does anyone have any evidence that it is a modern con with technical errors introduced by someone else? If not then it seems to be a WP:RS reliable source and may be used to support the article. Second, I have made that circuit and so I know it works. This is WP:OR and so cannot be used in the article, but should be enough to stop the bickering. (I was trying to re-create a crystal radio made by my grandfather during WW2 and so wound a coil like his on a wooden former, but used a schottky diode as a detector and an audio amplifier instead of Hi-Z headphones. My grandfather's design was capacitor-less with a sliding earth-tap on the coil, connected by sandpapering away some insulation lacquer after winding it. Adding a small trimmer capacitor increased the selectivity and 'peaked' the reception slightly, but still only the most local medium-wave station was really receivable). So, the circuit is authentic, and it works. What's the problem with mentioning it in this article? -- Nigelj ( talk) 08:29, 20 August 2010 (UTC)
P.S. A completely different inductance is needed with the capacitor compared to without it, for the same long wire antenna and same reception band. I can dig out my old experiments and count the turns if anyone's interested, but it's largely irrelevant as it's WP:OR, however it shows the principle is sound. -- Nigelj ( talk) 08:37, 20 August 2010 (UTC)
Several of the diagrams have a second capacitor labeled C2, on the headphone side of the diode. Given that the current on that side of the diode must be DC (albeit pulsating), what does C2 do? Mcswell ( talk) 04:25, 28 February 2021 (UTC)
I notice that, in addition to deleting the image, all mention of capacitance has been removed from the "Tuned circuit" bullet point at the top of the 'How it works' section. This is grossly false, and misleading to nontechnical readers, since it defines a tuned circuit as an inductor alone: "[A tuned circuit] . . . consists of a coil of wire called an inductor or tuning coil used to tune in different stations." Helllowwwww???? As the text made clear before it was eviscerated, a tuned circuit in a crystal radio always consists of an inductor and a capacitance, but some circuits use the capacitance of the antenna. The original description was thoroughly sourced. I don't want to be accused of continuing the above edit war, but unless somebody comes up with a compelling reason this dreck should stay, I'm changing it back. -- Chetvorno TALK 22:24, 20 August 2010 (UTC)
The slider in the illustration is on the right, not the left. —Preceding unsigned comment added by 68.42.44.186 ( talk) 13:22, 18 July 2010 (UTC)
The explanation of how the crystal detector is wrong. I have made several attempts to correct (perhaps not very well) but my edit is simply removed. There does not seem to be any point in correcting errors if the corrections are simply removed and the incorrect explanation retained.
david.tucker2@virgin.net Davidpetertucker ( talk) 17:09, 30 January 2011 (UTC)
Crystal detector
This explanation would only work is the signal measured several volts peak to peak.
Since the signal in only micro volts p-p how can a diode possibly rectify such a signal?
The real explanation relies on the fact that the diode is a nonlinier conductor and this mices the sidebands and carrier frequencies resulting in the recovery of the modulating frequency (among others). The purpose of the bias is to move the opperating point to the part of the diode's curve which maximises the amptitude of the desired signal.
— Preceding unsigned comment added by Davidpetertucker ( talk • contribs) 09:55, 2 February 2011 (UTC)
The latest revision is better because it avoids the false myth of "a knee in the diode curve," and is more small signal oriented. A technical explanation of this can take the frequency domain approach of collapsing sidebands, but that is very abstract for many. There is also a very clear time domain explanation that requires a very clear understanding of detection. 128.49.9.18 ( talk) 17:25, 9 November 2011 (UTC)
"energy of only 10−16 W/cm2"
W/cm2 is a power density NOT energy (which should be Joules). Someone put this right, please. 194.72.120.131 ( talk) 10:23, 11 May 2011 (UTC)
Do we need a section about how to make a radio that is ineffective at tuning? John ( talk) 04:43, 28 June 2011 (UTC)
Was this actually used in the day, or some contributor's original research? I've never seen a book or Web page describing this technique of setting a cat's whisker, and One thing that troubles me is how one is expected to hear anything in the headphones with a buzzer running within arm's reach. --
Wtshymanski (
talk)
22:32, 10 November 2011 (UTC)
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The article describes the impedance of the crystal (piezo) earpiece as being ~ 1 Mohm. This is the DC value. IIRC, the AC impedance is still quite low (~5kOhm), so a coupling transformer is desirable. Have I got this right? I haven't changed the article; someone better informed may wish to. — Preceding unsigned comment added by 87.194.171.29 ( talk) 02:29, 10 August 2012 (UTC)
In order for a radio to work it is necessary to have a ground connection or the radio needs a very large capacitance to act in lieu of the earth.
This requirement is similar to that for a power delivery system. The current from a power plant arrives at your home, it passes through various devices in your home and then travels to the ground wire in the circuit box and from there to a ground wire buried in the earth under your home. In a sense the earth itself is the conductor that returns the current to the power plant where there is a massive grid of conductors buried in the ground. The earth is not a great conductor but there is a lot of it and so it works. There is no wire that returns the current to the power plant. The earth could be replaced with a gigantic capacitor but that would be prohibitively expensive. Similarly, a radio needs either a ground connection or to be connected to a large capacitance that acts like the earth. The use of early crystal radio sets in aircraft and such was problematic due to the vibrations to which the radio was subject not due to grounding problems. I am not certain about the grounding of aircraft but will speculate that the tremendous amount of air through which a moving craft is passing will act like a sufficient ground/capacitance. Zedshort ( talk) 16:16, 12 September 2014 (UTC)
Well, this has been a truly fascinating exchange and collection of factoids. Now, would someone please explain the presence of a ground connection in diagrams of radios without using the circular reference of a counterpoise, and do so in twenty words or less. Thank you. Zedshort ( talk) 14:03, 13 September 2014 (UTC)
I have made a quite serious edit to this section. Given the interest in crystal sets evident in this talk page, it is likely that what I have done will prove to be controversial, so I shall try to explain. Firstly I have corrected the statement of the max power transfer theorem, so that it reads correctly. Impedances should not be equal for max power transfer, but one should be the conjugate of the other. I do not expect any disagreement over this. However, it seems to me that the only respect in which this theorem can be applied to a crystal set is that the impedance of the power source (i.e. the aerial) should be matched to that of the the load (the earphones). Ideally, the equivalent resistance of the tuned circuit at resonance should be severely mismatched to the source impedance of the aerial in order to minimise resistive losses in the tuned circuit, which can only be wasteful. If the tuned circuit were power matched to the aerial, maximum power would be transferred to the resistance of the tuned circuit, which is not what is required. It is for this reason that I have deleted all references to the idea of matching the aerial to the tuned circuit. Transforming the equivalent resistance of the aerial has significance in relation to selectivity, and this concept is best treated separately. Both topics (impedance matching for max power transfer to the headphones, and aerial resistance transformation for improved selectivity) are complicated by the fact that so many different crystal set circuits are used. In the circuit which accompanies the "Impedance Matching" section, it is clear that the left-hand slider can be used for tuning, and the right-hand one for impedance matching, and that the right-hand slider will also affect the Q of the inductor, and therefore the selectivity. In more complicated circuits where a variable capacitor is used for tuning, and the aerial is connected to a variable tap on the inductor, the useful effect of the different tap positions will be to improve selectivity when the tap is low, since then the Q of the parallel tuned circuit will be at its greatest. In this type of circuit, the resistance of the headphones will lower the Q of the parallel tuned circuit, so for greater selectivity, the resistance of the phones should be high. In this circuit, power transfer to the phones will also be affected by the tap position, so that the tap control can be used either to improve selectivity, or to achieve best sensitivity, depending on requirements. g4oep — Preceding unsigned comment added by 77.96.60.31 ( talk) 11:43, 4 January 2015 (UTC) G4oep ( talk)
Hi - I have looked at the paragraph you refer to, and although there is not much there to object to, I feel that the ideas involved in this section could be presented more rigorously. The paragraph starts by stating that the aim is to transfer power to the headphones, then states "Therefore, in better receiver circuits, to match the antenna impedance to the receiver's impedance...". The point that I tried to express in the material you deleted is that the first objective is not necessarily achieved when the second is fulfilled. True, it is necessary to match the receiver's aerial and earth terminals to the actual aerial/earth system in order to maximise power absorbed from the aerial, but then this absorbed power must be transferred to the phones with as little as possible lost in the tuned circuit. The resistive component of the input admittance of the receiver (considered as a parallel equivalent circuit) can be represented by 2 parallel components - 1) the transformed equivalent parallel resistance of the coil (or of the tuned circuit as a whole- Rc)) and 2) the transformed resistance of the phones/detector combination (Rp). For maximum power in the phones, Rc should be large compared with Rp since in a parallel equivalent circuit, the same voltage is applied to both resistors, and P is inversely proportional to R (P = V^2/R). This condition (Rc >> Rp) can be represented by saying that the antenna should be matched to the phones, and mismatched to the resistance of the inductor. That was what I wrote, and I feel that it should not have been deleted without proper justification. The resistances of the coil, and of the phones are indeed separable, and the design and adjustment of the circuit can be altered to control the fraction of the available power which is dissipated in each simply by adjusting their relative magnitudes. These magnitudes are under the control of the various transformation ratios. This idea is completely false: "maximizing power to the earphone also maximizes power lost in the coil". I have altered the text again. I expect that someone will quibble that the points I have made are not referenced, but it should be obvious to anyone who understands ac circuit theory that what I have written is correct; trust me - I am an engineer. If you don't understand circuit theory, don't change it. g4oep.
In the section about "use as a power supply" it states that AM stations modulate only 30 percent. This is only partially true. Aircraft navaid stations modulate their IDs 30% to leave room for voice modulation over the ID. But broadcasting stations routinely modulate 100% and even 125% in the positive direction. Can someone fix this please? 108.244.204.22 ( talk) 01:12, 10 January 2015 (UTC) Chip Veres 1-08-15 ]
Intro page says "By the nature of their operation, crystal radios can only demodulate amplitude modulation (AM) signals, not frequency modulation (FM) or digital signals."
Not true...
Crystal Radios CAN demodulate FM signals very easily. There's a number of HOWTO DIY pages on this.
See: http://scitoys.com/scitoys/scitoys/radio/radio.html#crystal for one example. or http://frank.pocnet.net/other/Sylvania/40_Uses_for_Germanium_Diodes.pdf or http://www.radio-electronics.com/info/rf-technology-design/fm-reception/fm-slope-detector-discriminator.php — Preceding unsigned comment added by 50.185.136.67 ( talk) 03:53, 31 March 2015 (UTC)
I've researched this question and concluded that reception of normal wideband FM is also possible with some crystal sets up to 30km from a transmitter. I've mentioned this fact and a link, but have found many more references during my research. We could probably use some wording to mention some of these as well, like their designs, efficiency, techniques etc. Main discussion of an optimized crystal discriminator design:
Slope detector vs. FM discriminator response curve:
Previous design:
Some others (also referenced above and from other places):
- bkil ( talk) 22:46, 3 July 2020 (UTC)
Recently the description of the crystal detector in the Design section bullet points was changed from:
to:
I think the previous version was better and should be restored. The detector is the most important part of the radio. I think it is important for readers to understand what it does; it demodulates the radio signal, separating the audio modulation from the carrier wave and producing the audio signal which is converted to sound waves by the earphone. The new text, in addition to being repetitive, doesn't make this clear. -- Chetvorno TALK 22:16, 7 May 2016 (UTC)
I might be being dumb and missing something fundamental, but wouldn't substituting the simple diode for four of them in a bridge rectifier provide a signal of twice the strength? After all, the idea for the envelope detection setup is to remove the inverse side of the original wave; if we instead invert it, we get twice as much positive signal. Yes?
Obviously this would be a massive pain to try and implement on an original oxide-coated-conductor and cat's-whisker type radio, but a semiconductor based model could use it... 209.93.196.109 ( talk) 20:14, 9 July 2016 (UTC)
The photo shows a boy wearing what appears to be a modern device of some sort. It is not really informative. Perhaps we can find a photo of an actual crystal radio and its associated circuit diagram. Zedshort ( talk) 13:51, 19 December 2016 (UTC)
From our German colleagues, a homemade set:
Capacitor tuned; up-close-and-personal diode.
Also, a nice crystal:
Glrx ( talk) 20:17, 28 December 2016 (UTC)
I agree that the current lede photo is unsuitable. It shows nothing about the topic and is much later that the important use of such radios, which was before WW II and certainly before transistors. I would suggest File:Kristallradio.JPG. It clearly show the cats whisker detector and the crystal and the headphones. There are several other views of this item as well. Images of modern crystal radios belong in a separate section on later usage.-- agr ( talk) 19:38, 27 July 2018 (UTC)
Assuming the wire of the coil is insulated, how is a sliding contact able to work? ZFT ( talk) 22:35, 20 January 2017 (UTC)
Editor LSMFT has removed all use of the term "cat whisker detector" from this article. I think this should be reverted.
The primitive semiconductor detector used in early crystal sets, which consisted of a fine wire touching a piece of crystal, was called either a "crystal detector" or "cat whisker detector" in literature of the time. The problem is, the semiconductor diode used in modern crystal sets is also sometimes called a "crystal detector", so a different term is needed to unambiguously distinguish the antique detectors. This article, following usage in most modern sources, called it a "cat whisker detector". LSMFT changed these terms to "crystal detector", claiming that 'cat whisker detector' was "not historically accurate"
LSMFT is wrong. In the first place, inventor Greenleaf Whittier Pickard named the device "cat whisker detector" when he invented it. Second, numerous wireless books of the time called it a "cat whisker detector". Third, even if they didn't, numerous modern reliable sources, technical and historical books and websites, call it a "cat whisker detector" (in modern sources the alternate form "cat's whisker detector" is usually used). This is probably the most common term for it today, used to distinguish it from various devices used later in the history of electronics, such as the germanium "crystal detectors" used in radar sets in WW2. Here are sources supporting these points:
-- Chetvorno TALK 21:44, 1 May 2018 (UTC)
Hello, Editor
Chetvorno.
The 14:26 1 May revision of the article did NOT remove all use of the term "cat-whisker detector". It was included, WITH CITATIONS, in the "Crystal detector" section of the article. The term WAS NOT deleted from the article completely.
Please carefully read the 14:26 1 May revision.
Thank you, LSMFT ( talk) 17:39, 2 May 2018 (UTC)
The article has a red link to square law detector. The article on decibel, and especially the case, especially in optics, where detectors give an output voltage proportional to input power, caused me to look for a square-law detector article. Gah4 ( talk) 03:01, 12 January 2019 (UTC)
@ Gah4: The reference is Lee, p.5-6. Bose's detector experiments are described in Sarkar, p.296-297, 482, see also Crystal detector#Bose's experiments. Bose's galena detector consisted of a tiny galena crystal with a point contact, mounted either in a horn antenna or at the focus of a lens, with a DC current from a battery through it. Microwave radiation caused an increase in current through the crystal, which he detected with a galvanometer. The DC forward bias would have moved the operating point up on the diode IV curve, making it unlikely that the junction was functioning as a rectifier. Lee says the current change was due to change in resistance of the crystal due to heating, as in a bolometer. One indication that it was not functioning as a rectifier is that Bose noted the detector also responded to light and ultraviolet. However other sources either aren't aware of or don't make this distinction, and just say Bose invented the first 'semiconductor detector'. -- Chetvorno TALK 00:36, 12 March 2019 (UTC)
Bose did not seek out a patent for this. Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves proving that communication signals can be sent without using wires. He sent and received radio waves over distance but did not believe it to be useful. EyesoftheOperation ( talk) 09:53, 18 October 2019 (UTC)
This article is mostly bogus. It is more or less someone's opinion and not factual. Nikolas tesla 1892 with a type of commercial patent later. Marconi came after Late 1890s- Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves proving that communication signals can be sent without using wires. He never sought to patent anything radio related because he felt they were technically useless. Tesla contributed more in the field of frequency communication with derivatives based on the simple radio oscillator he had put together, than any other inventor at that time. EyesoftheOperation ( talk) 09:52, 18 October 2019 (UTC)
There is no question that the radio signal can be used to power the radio itself, and the answer is yes. Billy Cheung (SP?) from Hong Kong has many youtube videos doing just that. Many are also FM, so yes there are FM crystal radios. Ex: https://www.youtube.com/watch?v=1q1qwCPC5kM There are other youtube videos online of LEDs and even a digital watch being powered. Ex: https://www.youtube.com/watch?v=0WvZC3-mR6Q It's not IF power from the signal can be used, but HOW MUCH. The answer is the amount is small, but usable. — Preceding unsigned comment added by 2001:FB1:C4:7F0:18A5:1040:337F:513A ( talk) 00:21, 31 January 2022 (UTC)