Talk:Crystal radio

message: 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.
*http://www.crystalradio.net/
**http://www.crystalradio.net/crystalplans/index.shtml
*http://www.crystalradio.org/
*http://www.crystalradio.us/index.htm
*http://scitoys.com/scitoys/scitoys/radio/homemade_radio.html
*http://www.ccmr.cornell.edu/education/modules/documents/CrystalRadio.pdf
*http://www.hobbytech.com/crystalradio/crystalradio2.htm
--220.101.28.25 (talk) 09:28, 6 December 2009 (UTC)
thread_title:  Broken Links 

message: 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)
replies: text: Read the last 3 sentences of the first paragraph of the "Crystal detector" section. --ChetvornoTALK 05:40, 28 February 2021 (UTC)
thread_title:  C2 

message: 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. --ChetvornoTALK 22:24, 20 August 2010 (UTC)
replies: text: I agree, it was clearer before (e.g. ) and I don't see any reason why the capacitor version should be expunged from the article. Maybe it can be better still with the compromise of introducing the capacitance inherent in a 'short' (detuned) antenna, and the possible use of this as part of the tuning 'tank', with disadvantages, when a capacitor is unavailable or impractical. I'm not sure where this new material should go, but somewhere in the 'How it works' section. --Nigelj (talk) 22:53, 20 August 2010 (UTC)
replies: text: Changed it back --ChetvornoTALK 23:05, 20 August 2010 (UTC)
replies: text: What I read now is better in my opinion.  I did not intend to remove 'all mention' of C, if I did (?) I got confused.  However, there are still substantial issues with this discussion of resonance, and how the antenna's L and C get tuned with reactances in crystal sets.  There is still wrong stuff being stated as fact; this topic is not trivial and kinda beyond the scope of most readers of this article.  I wish y'all would fix it or leave it to the antenna folks in the antenna article.  I would suggest consider omitting stuff rather than misleading people.  I hate to criticize without offering the solution, but I simply don't have time now.  John (talk) 05:46, 21 August 2010 (UTC)
replies: text: Sorry, I should have realized the capacitance thing was just an oversight.  I hope you'll explain about the errors you mention when you have time.  BTW, I appreciate you raising the issue of the tuning range of the "naive circuit", even if I disagree with your solution.   This article is kind of a specialized subject and I'm glad there are knowlegeable editors working on it.  --ChetvornoTALK 07:22, 21 August 2010 (UTC)
replies: text: No problem, I will try but it may take me a few weeks at least.  If someone else wants to take it on, that'd be nice; my hope was to leave it alone in this article but it keeps coming up.  This is involved because an antenna acts like both coils and capacitors and they depend on the frequency.  An electrically short antenna has too much C and needs L in the radio to tune the whole system of radio & antenna.  It also affects Z matching since X is part of Z = X + R.  The previous version of Fig 1 would have had to add too much L to tune with C, and the C would have needed way more range than any physically realizable variable cap could muster.  There are references for this issue in some of the old 1920s textbooks but thats another research project.John (talk) 16:39, 23 August 2010 (UTC)
replies: text: Yes, they used loading coils and capacitors to tune out the reactance of the antenna.  I didn't go into that in the "How it works" section, in the interest of keeping it short and accessible for general readers, but maybe something should be said about it.  Do you think the existing text states things that are false or misleading?  Where? --ChetvornoTALK 23:25, 23 August 2010 (UTC)
replies: text: To mention a couple, I think I see problems with the treatment of Capacitor in the Tuned Circuit section and the the Crystal Detector section is completely wrong in stating that detection efficiency is related to low forward threshold. John (talk) 14:16, 26 August 2010 (UTC)
replies: text: Yes; technically there is no sharp diode "threshold" but only the exponential IV curve.  But I didn't want to go into the Shockley equation and the resulting reciprocal relation between a diode's forward current and its small-signal AC resistance.  The idea of a "threshold" for conduction is an approximation commonly used for diode's IV curves.  It's an easy way for novices to visualize the detector's sensitivity problem, and especially why a bias voltage can improve sensitivity, by getting rid of the threshold.   Crystal radio detectors' lack of sensitivity is often explained that way, as shown in the references.  If you can come up with a better way, I'm all ears. --ChetvornoTALK 17:48, 25 August 2010 (UTC)

text: I think the best way to illustrate the problem, found in early books,  is to give a graph of a diode's IV curve with the applied sinusoidal voltage against the horizontal axis, and show graphically how it creates a very poorly rectified output current waveform.  Maybe such an image could be gotten from an early book and put in the article. --ChetvornoTALK 17:35, 25 August 2010 (UTC)
replies: text: You could make a real curve for a 1N34 with pSpice along with the real detected signal curves.  But more importantly, there is no sharp diode threshold, but further, there is no diode threshold at all, this notion is not even approximately right.  This comes as a shock to most engineers, but the diode curve has no knee (NONE) at all, it is a complete optical illusion.  Mathematically the diode equation (and real diodes conduction) is an e-to-the-x form curve (with slight variation, corrupted slighted by "n" the so-called efficiency parameter), and that has no point of max curvature (knee), it just does not exist.  Don't take my word for it, check the second derivative of a real 1N34 plot, or plot this and look at it on different scales, the "knee" changes.  I realize the notion of a knee is very popular (to the point it is emotional to many), but utterly fictitious.  It misleads people to think germanium diodes will always detect better than silicon.  Not true, it completely depends on the impedance of the radio tuner and transformed antenna.  A lot of crystal set design is substantially suboptimal because of this misunderstanding; being popular doesn't make it technically right.  It doesn't even make sense, though college professors actually teach this nonsense in top universities.  Reality is that, for signals weak enough for the curve to be approximated by a linear segment, the inverse slope of the IV curve at the operating point (AKA detection Z) needs to match the Z of the radio, again not a trivial issue.  It is a tough point to communicate, and few will believe it, I would suggest just deleting the wrong stuff in the article and reference some Agilent papers or something.  John (talk) 14:16, 26 August 2010 (UTC)
thread_title:  Removal of mention of capacitance in 'How it works' section 

message: 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)
replies: text: Fixed it.  Thank you very much for catching my screwup.  I must have had a touch of dislexia :) --ChetvornoTALK 16:20, 18 July 2010 (UTC)
thread_title:  The illustration incorrectly describes the slider 

message: 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)
replies: text: I wrote the original explanation, that used the "knee of the IV curve" language.  I was aware that this was an inaccurate explanation, but I thought that  "the signal voltage has to overcome the diode's forward voltage drop"   was a more concrete, visual way of explaining to a general reader why biasing the junction improves sensitivity (the same wording is used on many crystal radio websites, see refs).  I couldn't think of a way to explain the actual nonlinear curve understandably.  Davidpetertucker and others rightly pointed out that this was a bogus explanation. I reverted your edits; I felt at the time it was more important to keep it simple. 24.152.166.100 recently did a good job of correcting the explanation.  I understand the desire to correct the "myth of the knee" and present an accurate picture of small-signal rectification in a xtal set, but its inclusion makes the description of the how the diode works awfully "fuzzy".  --ChetvornoTALK 05:47, 10 November 2011 (UTC)
thread_title:  The detector 

message: "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)
replies: text: Fixed. But you can fix things, too. Wikipedia:Be Bold used to be a guiding principle around here. --Wtshymanski (talk) 13:52, 11 May 2011 (UTC)
thread_title: Wrong Units

message: Do we need a section about how to make a radio that is ineffective at tuning? John (talk) 04:43, 28 June 2011 (UTC)
replies: text: It wasn't really about construction and operation, was it? I"ve moved it to the discussion of tuned circuits; it's an interesting point and this was exactly the explanation I needed as a kid to explain why I could only get CFRW (1470) and never CBW (990) on any of the crystal sets I made or had given to me. --Wtshymanski (talk) 13:46, 28 June 2011 (UTC)
thread_title: Need to delete Construction section

message: 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)
replies: text: nevermind. ] says the WWI BC14A artillery spotter receiver (no tubes!) had a tuning buzzer. --Wtshymanski (talk) 22:44, 10 November 2011 (UTC)
replies: text: Yes, they were actually used. Check the reference at the end of the sentence, that's what its for. --ChetvornoTALK 23:49, 10 November 2011 (UTC)
replies: text:  Just because most Wikipedia references are junk doesn't mean I should always ignore them. A bad habit of mine. --Wtshymanski (talk) 15:32, 11 November 2011 (UTC)
thread_title: Buzzer?

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thread_title: File:Modern crystal radio set.jpg Nominated for speedy Deletion

message: 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)
thread_title: Crystal earpiece impedance

message: 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)
replies: text: I suspect Wtshymanski understood that; he may have been thinking of counterpoises.  As you alluded to, a lot of early crystal sets used capacitive grounding via a counterpoise instead of an earth ground;  that is what early aircraft and zeppelin wireless sets used.  1, p.312  From the early 1900s there have been portable crystal sets carried on the body which could not have earth grounds.  For example, in the photo at the top of the page, the crystal radio the boy is listening to does not have a ground wire, but is grounded sufficiently by the capacitance of his body through his hand holding the set.  --ChetvornoTALK 16:56, 12 September 2014 (UTC)
replies: text:  Cell phones.  Airplanes. Spacecraft.  How much capacitance is there between a satellite in synchronous orbit and the Earth?  A Mars rover and the Earth?  (For that matter, light is just really really high frequency radio waves and propagates just fine over intergalactic distances.) The Tesla model is inappropriate - radio receivers work with the free space field and any use of earth is for convenience.  At the frequencies used for AM broadcast, it's inconvenient to build an antenna that collects enough power to operate an earpiece, so you use the earth as part of the system  - but it's not really correct to think of Tesla-style currents running through the Earth from transmitter to receiver. --Wtshymanski (talk) 23:59, 12 September 2014 (UTC)
replies: text: What are you basing the above upon? Is it just opinion? A ground is shown in most all diagrams of radios. Why are they shown? What purpose does a ground have? In the case of a rover or spacecraft, they too have enough capacitance to function as a ground. Your injection of a counterpoise into the definition makes no sense. A counterpoise is used in the case that a proper ground cannot be made at the transmitter site.  Zedshort (talk) 04:42, 13 September 2014 (UTC)
replies: text: Zedshort, were you addressing Wtshymanski or me?  A crystal radio does not have to have a ground, it could use a dipole antenna; it's just that with the long wire antennas needed, a dipole would require a second long wire, doubling the length of the antenna, to give the same reception.   A monopole, due to the ground reflection, has 3 dB more gain than an equivalent dipole.    Another issue is that AM stations broadcast in vertical polarization, so a horizontal dipole isn't as efficient as a vertical monopole.  A crystal radio with a monopole antenna without a ground can also work,  because the radio's case and the hand holding it can function as the other half of a dipole antenna.  It will be much less sensitive but is probably adequate for the strong signals in an urban area. --ChetvornoTALK 10:14, 13 September 2014 (UTC)

text: A dipole antenna does not use a ground, but a monopole antenna, which is what was used with crystal radios, requires the other side of the transmitter or receiver to be connected to some type of conductive ground plane, which functions as a reflector, not a radiator.   1, p.142   It doesn't have to be connected to the Earth.   The size of ground plane required depends on the frequency, it should ideally extend at least a quarter-wavelength from the antenna.   The MF and LF broadcast freqs received by crystal sets require a large ground plane, at least 1000 ft in dia., so the Earth is the most convenient conducting plane available.   If an Earth ground connection cannot be made, a counterpoise, a wire screen capacitance to Earth, can be used.  1, p.142,   2, p.523    "Counterpoises" were widely used during the wireless era for receivers as well as transmitters.   3, p.157,  4, p.217,  5, p.278,   6, p.311-312,   7, p.45  However early radio researchers didn't really understand how they worked.  If a counterpoise is too small or too far away from the Earth, its voltage will not remain constant and it will radiate (or in a receiver pick up radio waves), simply functioning as the other half of a dipole antenna.  That is actually how the whip antennas in modern walkie-talkies, CB, and portable FM radios work.   8,    9, p.53,     10, p.48-49  The whip is nominally a "monopole" antenna, but the other side of the transmitter or receiver is merely "grounded" to the radio's chassis or circuit board.  So the chassis and whip function as the two halves of an asymmetrical dipole antenna.  This is also how small portable crystal radios without grounds work. --ChetvornoTALK 09:04, 13 September 2014 (UTC)

text:   This photo shows a woman in 1922 with a crystal radio in a parasol.  It has a wire antenna in the parasol, but is not grounded.   The radio itself and the woman's body function either as the "ground" or the other half of the antenna.  If they have enough capacitance to ground they function as a counterpoise.  If not, they function with the parasol as the two halves of a dipole antenna; the incoming radio wave induces opposite phase oscillating voltages in the antenna and the radio's case including the attached earphone wires, etc. which constitutes the input signal applied to the tuned circuit.  --ChetvornoTALK 09:04, 13 September 2014 (UTC)

text: Sorry, I may have had too much coffee last night.  What it boils down to is: The oscillating current from the wire antenna, after passing through the radio, needs some conductor with a high capacity to flow into.  The Earth is ideal, but it doesn't have to be the Earth. --ChetvornoTALK 18:47, 13 September 2014 (UTC)
replies: text: So, in order for a current to slosh back and forth within a circuit, the charges needs something to slosh into and out from that has lots of space to allow the sloshing, that thing being a capacitor. Whether the antenna is connected to the ground directly via a conductor into the ground or coupled to the ground by a counterpoise makes no difference, provided the capacitance is sufficiently large relative to the need. But of course, in writing the article, that idea needs to be expressed. Should the article describe the "ground" as a very large capacitance? If it is described as I did, as a large reservoir, that might work. The ground wire analogy with a physical connection back to the transmitter obviously fails in the case of spacecraft communications. Zedshort (talk) 20:05, 13 September 2014 (UTC)

text: The simple statement is that crystal radios need good antennas because the power that drives the headphones comes from the antenna. The more power the antenna delivers, the better. A half-wave dipole is a good antenna, and it does not need a ground (but for practical reasons might need a balun). Over-the-air powered RFIDs can use dipole antennas. AM transistor radios also used ferrite loopsticks; they capture the magnetic field and do not need a ground. Consequently, a good ground is not a requirement. Back when crystal radios were popular, the operating frequency was low, the transmitted power levels were high (that pesky atmospheric noise required it), and people often used a crappy, untuned, single-ended, long-wire antenna. Grounding those antennas improved them. If the ground were perfect (which it isn't), it would make an image antenna and cause current to flow in the antenna wire. Simplistically, if there were no connection to ground (and no capacitance to ground), then no current (and no power) would flow from the single-ended antenna. Glrx (talk) 01:17, 15 September 2014 (UTC)
thread_title:  Ground connection 

message: 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)
replies: text: I don't agree with your idea that maximum power is produced by mismatching the impedance of antenna and tuned circuit; neither do any of the sources cited in the article.    The aerial is connected to the crystal/earphone circuit through the tuned circuit.  Although there are many different circuits, the load resistance the aerial sees is some parallel combination of the resistance of the crystal/earphone circuit and the parasitic resistance of the tuned circuit (scaled by the impedance transformation of the antenna tap on the coil).   You can't separate those two resistances. To transfer max power to the earphone, the antenna must be matched to the impedance it sees, which is the parallel combination; that's what the maximum power transfer theorem says.   The max power theorem doesn't discriminate between resistances in the circuit; maximizing power to the earphone also maximizes power lost in the coil. --ChetvornoTALK 21:02, 31 March 2015 (UTC)
replies: text:  The issues are much more complex than transformer matching. I reverted to the sourced version. Glrx (talk) 01:29, 7 April 2015 (UTC)
thread_title:  Impedance Matching 

message: 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)
replies: text: They might have peak modulation that high, but as a power source it is average that counts. With no modulation, an AM transmitter runs at 1/2 of power that it does at full modulation. (That is, half the power in the carrier, half in side bands.)  Also, carrier power (no modulation power) is 1/4 of Peak_envelope_power. Gah4 (talk) 04:40, 12 March 2019 (UTC)
thread_title:  Modulation fix wanted 

message: 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)
replies: text: I agree.  Slope detection is a time-honored way of demodulating an FM signal with an AM radio, although I don't know how much this technique was used with crystal radios. --ChetvornoTALK 06:21, 31 March 2015 (UTC)

text: Well, I would be careful... I don't see anything in the three references above that actually says it has been successful in practice (although I haven't read every word in each of them - perhaps someone will quote the relevant bit(s)). First, the reception bandwidth of many practical crystal sets is very wide, due to lack of good filtering or tuning. This means there isn't much 'slope' anywhere to perform the FM to AM conversion. Secondly, the power capture of a traditional crystal set depends on a very long (e.g. hundreds of feet) random wire antenna. These are not much use at VHF, where most FM is transmitted, and would not capture more received power than a one or two meter tuned dipole. I don't know that such short reception antennae, even if tuned, would ever pick up enough power to hear directly unless one was very close to a transmitter. (VHF transmitters don't put out megawatts, as they know the range will be limited by line-of-sight anyway). I'd like to see a quote from an actual WP:RS before stating that crystal radios are practical on FM bands. --Nigelj (talk) 19:41, 31 March 2015 (UTC)
replies: text: Good points.  Even if it has been done just to prove it was possible, that's a long way from saying it is a practical technique.  Without more specific sources I don't think FM reception should me mentioned in the article. --ChetvornoTALK 20:26, 31 March 2015 (UTC)
replies: text: There is discussion, I believe in the FM article, on a narrow-band FM broadcast system preceding the current system, and that could be demodulated by AM receivers. But we don't have transmitters like that, so it doesn't apply now. Gah4 (talk) 02:59, 12 January 2019 (UTC)
thread_title:  Crystal Radios CAN demodulate FM signals! 

message: 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)
replies: text: The major issue with the diode detector used to rectify the weak signals in a crystal radio is the forward voltage drop of about 0.3 V (in germanium) required to turn it on and begin rectifying.     A bridge rectifier has two diodes in series in the signal path, and thus has twice the voltage drop.  I remember seeing a discussion of the bridge rectifier in crystal radios somewhere on the web, and the conclusion was that it was not better. --ChetvornoTALK 23:50, 9 July 2016 (UTC)
replies: text: Yes. Even for low voltage power supplies, the loss is too much. Consider the 3.3V supply common for computers now, and lose 1.4V (two Si diode drops) instead of one.  But two diodes and a center-tapped transformer give only one diode drop. Can you use a center tapped coil for a crystal radio? Power supplies now use a synchronous rectifier switching FETs on and off. Gah4 (talk) 04:45, 12 March 2019 (UTC)
thread_title:  Why not a bridge rectifier? 

message: 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:
*"Hence we have the familiar cat whisker detector",   Bucher, 1920, Wireless Experimenter's Manual, p.167 
*"Cat Whisker Detector",    Popular Electricity and the World's Advance, Vol.6, No.1, May 1913, p.585
*"Galena detectors are often spoken of as "cat whisker" detectors because of the long fine wire used...",    Morgan, 1914,  Wireless Telegraph Construction for Amateurs, p.199
*"Fig. 7 shows the drawings of a novel type of cat whisker detector",   James White, 1920, Practical Amateur Wireless Stations, p.27
*"...and you will have what is called a cat whisker detector",    Collins, 1915, The Book of Wireless, p.205
*"Such structures were later to become the basis of the famous cat's whisker detector, which revolutionized the practice of receiver design...",        John Orton, 2004, The Story of Semiconductors, p.20
*"The transistor...in its early form was similar in construction to the cat's whisker semiconductor diodes in use in radio.",     Morton, Gabriel, 2007, Electronics: The life story of a technology, p.26
*"This is also known as a cat's whisker detector",      Kumar, Shukla, 2014, Concepts and Applications of Microwave Engineering,  p.211
*"Pickard branded it as the 'cat’s-whisker detector'",      Riley Shaw, The cat's-whisker detector, personal blog
*"With two associates, Pickard founded the Wireless Specialty Apparatus Company to market 'cat's-whisker' crystal radio detectors",   1901: Semiconductor Rectifiers Patented as "Cat's Whisker" Detectors, Computer history timeline, The Silicon Engine 
*"...early receivers used primitive devices such as the cat's whisker detector..."    "Electronics", Encyclopaedia Britannica online
*  Carr, 1991, Old Time Radios! Restoration and repair, p.8
*"This device became known as the cat's whisker detector",    Jensen, 2013, Wireless at War
*"These crystal detectors were originally made from a piece of crystalline mineral and... often referred to as cat's whisker detectors.",   Manes, Pelosi, 2015,  Enrico Fermi's IEEE milestone in Florence, p.25
*"The first true detector rectifier was also the first true solid state device, affectionately known as the cat's whisker detector of crystal radio fame",    Braun, McDonald, 1983, Revolution in Miniature: The History and Impact of Semiconductor Electronics, p.11 
--ChetvornoTALK 21:44, 1 May 2018 (UTC)
replies: text: No, not completely deleted, but only one use was left, buried in the "Crystal detector" section.  The word "whisker" is used in two captions; readers are not going to know what that means if they don't happen to notice the term "cat whisker detector" in that section.  I think the term "cat whisker detector" needs to be more widely used to distinguish the early detectors.  The problem is the term "crystal detector" is overinclusive.  --ChetvornoTALK 03:29, 3 May 2018 (UTC)
replies: text: I have always heard them described as cat's whisker, I suppose maybe cat whisker, though usually soon indicating that it is actually metal and not a part of a cat. Gah4 (talk) 01:42, 12 March 2019 (UTC)
thread_title:  Removal of term 'cat whisker detector' 

message: 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)
replies: text: I personally don't think it merits a separate article, because there is not really a separate type of detector called a "square law detector".  Square law detection is just the mathematical regime that a rectifying detector like a diode operates in when a small-amplitude signal is applied to it; the DC output is dominated by the 2nd order term in its Taylor series so the output is proportional to the square of the signal amplitude (as opposed to at large amplitudes, at which the output is proportional to amplitude) .  But I think a section on "Square-law detection" explaining it should be added to Diode, Crystal detector or this article, and the article should link to it.  --ChetvornoTALK 11:51, 12 January 2019 (UTC)
replies: text:  If the concept is mentioned in a few articles, then it is a separate idea and a separate article could be appropriate. In general, a nonlinear device can have its transcribing function expressed as a Taylor series. The even power terms generate a DC component. Semiconductor diodes have an exponential transcribing function. FETs are often characterized as drain current is the square of the gate-to-source voltage. So the article could cover the math and give examples. More specifically, the square law detector can function at frequencies where it is difficult to get gain, such as optical frequencies. The early crystal detectors were before vacuum tubes / radio frequency gain devices. Glrx (talk) 16:45, 12 January 2019 (UTC)
replies: text: In optics, and much of quantum mechanics, there is much discussion of amplitude and intensity, where intensity is the absolute square (it might be complex) of the amplitude. In simpler system, power is proportional to the square of voltage or current, without dependence on Taylor polynomials, but just ohm's law. Absorbed optical power, which might generate a photocurrent, is proportional to the square of the amplitude of the EM (light) wave. But, yes, also in the case where of the second order Taylor series approximation. Gah4 (talk) 01:50, 12 March 2019 (UTC)
thread_title:  [[square law detector]] 

message: 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)
replies: text: I agree the History section is not very good.  However, the claim that Tesla invented the crystal radio is totally wrong, not found in any reliable histories but only WP:FRINGE WP:PSEUDOSCIENCE websites.  Tesla had nothing to do with the development of crystal detectors (see the thoroughly sourced Crystal detector#History section).  Tesla invented the inductively coupled resonant transformer in 1891, which was used in both transmitters and receivers in the famous "four-circuit" radio design, later employed in crystal receivers throughout the early 20th century.  But it was Oliver Lodge, John Stone Stone and Karl Ferdinand Braun that first applied the circuit to radio receivers and transmitters.  Braun and Marconi received the 1909 Nobel physics prize for this.  Tesla only used it in his wireless power experiments, and did not develop a radio system until after these others;   and see the "Tuning" sections in the thoroughly sourced Radio receiver#History and Spark-gap transmitter#History.  The electronic oscillator was invented by Elihu Thomson, William Duddell, Valdemar Poulsen, Edwin Armstrong, and Alexander Meissner; see the thoroughly-sourced Electronic oscillator#History section.  --ChetvornoTALK 09:12, 20 October 2019 (UTC)
thread_title:  Nikolas Tesla invented the crystal radio! 

message: 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)
replies: text: YouTube is not a reliable source.  This section has only one source -  which is in Russian.  It needs more. Also to my knowledge the few examples of circuits using radio wave power to run a amplifying receiver have been experimental hobbyist projects in amateur electronics magazines. The section should probably make that clear, and be scaled back to avoid WP:undue weight --ChetvornoTALK 03:22, 31 January 2022 (UTC)
thread_title:  Use as a power source - Topic/Heading