Talk:Crystal radio/Archive 1

Archive 1

sections

Will add a How-to section in the next few days. — Preceding unsigned comment added by Robertkeller (talk • contribs) 06:00, 23 May 2003‎

Should you combine it with the Construction section? — Preceding unsigned comment added by JA.Davidson (talk • contribs) 20:08, 18 November 2006‎

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)

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)

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)

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)

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 "Oat Box Radio" looked odd to me too, until I figured that: 1) Station tuning is by the resonant circuit formed by the 100pF capacitor and the part of the coil in parallel with it. The only way to retune is by changing a tap on the coil. The manual says that making more taps will make tuning "sharper". That is not the right word since the resonance Q-factor can not be increased that way. 2) I believe the earpiece is a crystal type not an inductive type. A crystal earpiece resembles a capacitor, hence it does not pass current and discharges via the 47 kilohm resistor connected in parallel. (A personal reminiscence is that the first crystal set I tried to make was similar to this design. It made no sound at all. Later I found my error had been to wind my coil around a tin can.) Cuddlyable3 (talk) 08:48, 17 December 2008 (UTC)

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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.

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CONSTRUCTION Section Needs Work

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)

Not sure what the Construction section is doing but it has a number of problems: It introduces the concept of the simplest radio yet fails to use the simplest circuit, (which should be a coil without the tuning capacitor across it.) If someone actually builds this for the Broadcast Band, it will not tune the whole band because of the fixed antenna capacitance across the variable capacitor. Some mineral detectors are not crystals, like Lead Peroxide. Cadmium sulphide is not a reasonably good detector. The detector does not need to be (and not even typically) mounted in a brass cup (it is typically potted in Woods metal.) The cost of the antenna wire is off topic. The “…provides audio output in proportion to signal strength of signal …” is misleading in 2 ways. The “passive” and “no amplification” is redundant. The statement about “no way to control volume” is not necessarily factual. The paragraph about detection efficiency is rambling.

Anyone think we should keep this section?

John 05:08, 19 April 2007 (UTC)

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Diagram

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.

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This diagram?

What is confusing about it?

69.76.192.205 20:06, 24 December 2006 (UTC)

Answer to 69.76.192.205 question: what is confusing about the above diagram: Except for antenna and ground, all of the schematic symbols are non-standard, they are made up in such a way that they are not symbolic enough of the parts to wikify. These are not even antique versions of the symbols. Why not use standard symbols so all can understand? John 05:23, 19 April 2007 (UTC)

really they are all easy to understand. Capacitor ... antenna ... crystal rectifier ... headphones ... and the ground ... J. D. Redding 02:57, 11 May 2007 (UTC)

Oh yea .. forgot to say ... thereis a rheostat coil there too ... J. D. Redding

Reply to J. D. Redding. Why use non-standard symbols? We don't need to make up symbols; it demonstrates lack of knowledge and cannot be researched (except for the antenna symbol.) We should not be introducing readers to incorrect symbols. This should be changed to a wiring pictorial or a valid schematic. Besides being out of place and unreferenced, there are technical problems with this diagram. The antenna and detector should be connected to the same point on the coil, or in a more complex circuit the detector connection separately adjustable. The capacitor is for VLF use only, and invites confusion with use as a tuning capacitor. Does it have enough value to retain? Can we fix and reference it or delete it? John 20:38, 15 May 2007 (UTC)

Technical problems with this diagram? What? This is one of the many different types of crystal radio circuits (not recognizing this is something that demonstrates a lack of knowledge about crystal radios). The circuit works too ... because this is the one I built and received sound on. No need to "fix" something that is not broken ...

This is symbols that are used in various crystal radio diagrams. Have you looked at alot of crystal radio diagrams from the 1920s up to now? These symbols have been used ... and can be used. Does not have to be a certain "wiring pictorial" or a certain type of schematic. Do you wanna change the G. W. Pickard picture because he isn't using "valid schematic". J. D. Redding 21:59, 17 May 2007 (UTC)

Historic schematics made before standards do not necessarily use standard symbols for obvious reasons. People who draw schematics today are expected to do so. I don't think you can reference a historic schematic that uses that capacitor symbol? Or coil? Could you please explain the problem with correcting it? I can do it. John 05:19, 29 May 2007 (UTC)

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)

It would be a strange TRF receiver that re-radiated enough signal to be distinguished from the background by another receiver at a distance, yet not oscillate due to feedback to itself. Cuddlyable3 (talk) 08:59, 17 December 2008 (UTC)

Apparently it is possible to remotely detect the presence of semiconductor p/n junctions, such as the diode in a crystal radio. Apparently you transmit an RF signal, and the semiconductors 'receive' it and give off a characteristic signal (harmonics?). This was reportedly used in the days when electronic devices were far less common. IF it works it may now be impractical as there are so many electronic devices around. Too many 'false' positives. --220.101.28.25 (talk) 20:31, 26 October 2009 (UTC)

Found it! See this article, Nonlinear junction detector short but interesting! --220.101.28.25 (talk) 00:33, 6 December 2009 (UTC)

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 . 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)

No. You describe an Avalanche diode, which is an active device. The radio is then no longer a Crystal set. Gutta Percha 10:04, 13 June 2007 (UTC)

Proposed Elevation of Cristadyne Sect to new article

The Crystadyne section is facinating, but not squarely on topic for this article. It is an early discovery of solid state amplification instead of passive crystal radio. I plan to remove it and create a new stand alone article with it if there are no objections. John 22:02, 10 May 2007 (UTC)

Good Idea. In the early days there were many references to amplification using crystal detectors with multiple "catswhiskers" and bias. It is clear that Schottky was familiar with this work when he first set out to develop the Transistor. Gutta Percha 10:12, 13 June 2007 (UTC)

This crystal radio article is attracting a lot of amplifier schemes that use power from the signal. There are many more out there that have not been cited yet. Some of these cannot work because they violate laws of physics. Others are misunderstandings of how the circuit really works. So far, none have worked better for receiving weak signals than plain half wave rectification with attention to impedance matching. I think they should all be moved out of crystal radio. Maybe they belong as historic background under amplifiers. Or maybe there is a better idea? John 15:42, 13 June 2007 (UTC)

Frequency coverage

Can somebody familiar with classic sets and recent experimentation comment on the range of frequencies/wavelengths which this type of receiver is effective with? I note elsewhere reference to around 300m and there's an old story (possibly apocryphal) of picking up 2LO [350m] with a coil of wire wrapped around your hand and a bit of coal :-)

Noting that Russia has just booted out the BBC there could be a revival of interest in simple receivers as an alternative to Internet-distributed news which is too easy to monitor or block. MarkMLl 10:39, 18 August 2007 (UTC)

We here build regenerative radios ;)) There are two circuits for FET and BJT respectively, we call it "three-pointie" ("трёхточка", "trehtochka" in Russian) - almost nothing is needed beyond a throttling pot, transistor, LC and 1,5V cell. —Preceding unsigned comment added by 85.140.16.75 (talk) 19:53, 9 September 2007 (UTC)

Frequency coverage on the low end is not limited, lower than 20KHz is practical. On the high end it may sometimes be limited by detector self-capacitance or wiring style, 100 MHz (FM slope detection) is not uncommon. Note however, this is not a general discussion page. John 01:19, 10 September 2007 (UTC)

Thanks, John, very interesting. I wonder whether it would be worth adding some comment to the main article to make clear it's applicable to more than antique LW AM? Hopefully somebody will write up the трёхточка somewhere, it sounds fascinating MarkMLl 21:21, 10 September 2007 (UTC)

Valid point, Mark. Maybe I will do that, thanks. John 01:21, 11 September 2007 (UTC)

future of crystal radio?

One item I'd like to see addressed is the future (or end?) or crystal radio. As you may or may not know, in the USA, TV broadcasts are being FORCED! to broadcast digitally. Soon they will shut down the analog broadcast transmitters. 2009 is current target date.

Well, radio in the US and I am sure various parts of the world is showing a voluntary trend in the same direction. I hear FM stations, and yes, AM stations bragging they they now, or will be broadcasting digitally. FM claims CD quality sound, AM claims current FM quality sound from an AM digital format. New digital receivers are slowly making their way onto the market.

I don't think anyone is going to come up with a crystal digital receiver as the radio industry evolves. —Preceding unsigned comment added by Bth8446 (talk • contribs) 16:02, 9 October 2007 (UTC)

AM radio is still the main broadcast medium in much of the third world and likely to remain so as long as they require only the cheapest kind of receiver (Matthew 26:11, Mark 14:7, and John 12:8). Crystal radios can as now be kept alive by enthusiasts for a long time yet. I don't expect the USA to outpace the rest of world in going to digital broadcasting to such an extent that millions of AM receivers owned by Americans become useless. See WP:BALL. Cuddlyable3 (talk) 09:18, 17 December 2008 (UTC)

Problems with 3 slider "Improved Circuit" article

Loading the antenna to the tuned circuit will make the RF resistance of the tuned circuit become the load, leaving too little power for the detector.

The antenna is not up to 72 ohms in resistance but far beyond.

Antenna reactance is not due to antenna capacity.

Earphone impedance should properly load detector, not highest possible.John (talk) 23:51, 18 November 2007 (UTC)

Drifting Away From Crystal Radio

This article has drifted far from crystal radio. The 20' & 30's section contains almost nothing about crystal radio. Other sections contain amplifier discussions and other unrelated information. These are interesting but are misplaced here. This material should be removed or moved to other articles. John (talk) 02:31, 9 January 2008 (UTC)

This is an encyclopedia, not a how it works booklet for pre-grades

"Then it uses a crystal detector to convert this radio wave electricity back to sound electricity." C'mon! 131.203.76.50 (talk) 08:01, 16 April 2008 (UTC)

C'mon yourself. I strongly disagree, this is an encyclopedia for everybody. As a teacher of young readers, I commend efforts to include easily understandable material. We need more considerate articles. —Preceding unsigned comment added by 64.203.52.78 (talk) 01:55, 24 May 2008 (UTC)

I recently removed this section, but it was re-instated with the comment "Don't think there is a consensus on removing it". Well, let's discuss. IMO, this section was badly written, and as I said in my edit summary, simplistic to the point of gibberish. "This electricity is connected to the crystal radio by the antenna and ground wire."? "convert this radio wave electricity back to sound electricity"? "It uses earphones to convert the sound electricity to sound you can hear in the earphones"? This is unencyclopaedic meandering, and there's no reason for its retention. Wikipedia isn't specifically written for "younger readers", and whilst of course I'm not suggesting we alienate such readers, we shouldn't be gearing the article prose at the reading comprehension of a six year old. Oli Filth^(talk) 21:39, 26 May 2008 (UTC)

I agree it does not use big words or customary technical jargon for EE, but it is grammatically correct and I do not see a technical flaw in it; actually it is precisely correct, technically. Guess I don't know what 'unencyclopaedic' means. It seems to me to stay on topic, I must have overlooked the meandering part. I see no problem with keeping this as at least one section that is understandable by laymen, or even 'young readers.' However, if you have a better suggestion... John (talk) 23:34, 6 September 2008 (UTC)

I agree with Oli Filth that the quoted text is ridiculously dumbed down. The sentence The crystal radio uses a tuner to tune the electricity to receive just one station. is laughable. It does no service to any reader of any age to describe different "kinds" of electricity. JA.Davidson, that is far from precisely correct, technically.

The heading "How it works (simple version)" is silly when it is the only version on the page. Cuddlyable3 (talk) 20:38, 15 December 2008 (UTC)

I also agree that this section needs work and is a little confusing to read due to the attempted oversimplification. Perhaps it should be rewritten to refer to energy rather than electricity, ie "radio stations convert sound wave energy into radio wave energy and broadcast it...antenna recieves radio energy & converts to electrical current...coil/cap tunes specific frequency of ac current...crystal detector converts radio frequency ac current to sound frequency current...earphones convert electrical current to sound wave energy" - thoughts? StealthFox 12:47, 16 December 2008 (UTC)

The radio wave has the same energy whether silence or sound is transmitted. Cuddlyable3 (talk) 14:24, 16 December 2008 (UTC)

I was under the impression that it was the amplitude of the carrier wave that was modulated, which would change the energy of the wave surely? Or have I got the wrong end of the stick? regardless, perhaps "recovers sound frequency current from the recieved radio frequency current" or similar would be a better wording StealthFox 14:43, 16 December 2008 (UTC)

We understand that AM does not add to or subtract from the averaged energy (power) of the carrier wave, while you are right that the instantaneous energy (power) changes both up and down when there is a sound. The text should not say that the radio wave energy is a converted form of the sound wave energy, for the reason I stated.

RECEIVED is the proper spelling. Cuddlyable3 (talk) 19:59, 16 December 2008 (UTC)

Non-electric amplification

This is unsourced, and while interesting (if true), at present it's tangential to the topic. Perhaps it could be folded into Loudspeaker. 69.22.250.169 (talk) 22:00, 29 January 2009 (UTC)

Moving the content to Loudspeaker would not solve the lack of souces and it would be misleading to imply that these are viable loudspeaker designs today. Eventually the information could be moved to Sound recording and reproduction#History. Cuddlyable3 (talk) 13:06, 12 June 2009 (UTC)

Power source

I'll bet that non of the people writing this article can explain why the radio can drive a headphone with only radiowaves... There simply is not enough power obtainable and the density is not enough, but researching this fact would be regarded pseudoscience. Ignorance makes the world a sad place, hopefully things will one day change... --Nabo0o (talk) 22:15, 11 June 2009 (UTC)

The power density really is enough, not only to drive a headphone but in the case of Hertz' experiments to produce a visible spark in a receiver spark gap. The "How it works" section is poorly written with unclear phrasing such as "recovers the original sound frequency current from the radio frequency carrier". Cuddlyable3 (talk) 13:06, 12 June 2009 (UTC)

I agree. There isn't much power from the aerial but there is enough the power the radio. Crystal radios operate perfectly satisfactorily at microwatt power levels. Take a look at the typical modern crystal earpiece and how it differs to other modern headphones - the whole design is optimised to send tiny amounts of sound into the ear in a way that makes even very quiet sounds audible, but even then the signal is not particularly loud. Basically, the whole design is optimised to work at miniscule power levels. In any case, I notice that you are quick to dismiss the gerneally accepted view of how a crystal set is powered but do not offer any alternative interpretation. CrispMuncher (talk) 14:35, 12 June 2009 (UTC)

I am sorry for for that, but I had my reasons, as the aforementioned "pseudoscience-stamp" would immediately have been evoked. The energy density of radio-waves in an area normally distanced from emitters is not a whole lot, and I was thinking specifically of the crystal radios which was strong enough to power a small speaker audible through several rooms, as they actually exists though are less known to the general public. One such circuit has been named "the crystal mystery set" and the circuit is discussed at these links:

[1]

[2]

The explanation to why I think that it can power a larger load than what the radio waves themselves could possibly manage is not perpetual motion or over unity, as these explanations are mostly used by the very "debunker's" that wants to prove the phenomenon wrong. The answer lies in several established facts, combined with observations which many private experimenters have observed related to resonance as a way to amplify power. If you study particle physics you will learn how all observable energy is ultimately a result of the constantly appearing and disappearing particle flux, which because of its strange behavior have been called the 'virtual particle flux'. Energy is constantly being created and destroyed (at least as far as todays scientists can reach in terms of observation), and so explaining an extra influx of energy would be no more of a problem than saying that the symmetry for a given reaction was not completely perfect, and so more energy was gained by the constantly energetic particle flux than what was used to excite it. This is also where the term COP (coefficient of performance) is better to use than efficiency, since it describes the reaction better than an efficiency calculation. --Nabo0o (talk) 14:12, 13 June 2009 (UTC)

The two links above describe crystal sets such as "The Mystery Crystal Set" that feature multi-section coils where the coil connected to the tuning capacitor has no direct earth connection. This is not very mysterious because the coil sections are coupled together inductively, since they are wound on the same former, creating a transformer. Stray capacitance provides a route for the antenna signal to earth. Partly isolating the resonant circuit this way helps achieve a high Q factor which explains the "mystery" of these radios' good performances. The established understanding of the resonance here is that it does not "amplify" power, instead it provides an optimum power transfer from the antenna to the detector at the resonant frequency. Postulating that there is an unproven "extra influx of energy" that needs to be explained by ideas from particle physics is WP:OR. I do not regard any research as pseudoscience but invoking special explanations for common phenomena and disparaging anyone who is unconvinced as "ignorant" and/or a "debunker that wants to prove [a] phenomenon wrong" is characteristic language of pseudoscience. Cuddlyable3 (talk) 20:43, 13 June 2009 (UTC)

I agree - there is nothing mystical about this circuit. Here the coil is doing double-duty as tuning component and audio transformer. On the aerial side that increases the impedance of the load. Since the aerial has has incredibly high output impedance this increases the voltage generated in the circuit. On the earpiece side there is a current boost at the expense of voltage. Ultimately this modified design simply provides a better match up between the characteristics of the aerial and the earpiece - you don't get something for nothing.

As regards the whole vacuum energy stuff, this is nonsense. You can't tap vacuum energy as a power source - doing so fundamentally breaks the conservation of energy. I'd suggest reading up on the reasoning behind Hawking radiation. Even under extreme conditions (in this case near a black hole) everything has to balance. This is so well understood that it changed our understanding of black holes. CrispMuncher (talk) 18:55, 14 June 2009 (UTC)

The multisection coil works as a radio frequency not audio frequency transformer. A long outdoor aerial has a significant capacitance to earth and hence presents a low impedance though practically infinite resistance. For this reason it is advantageous to couple the aerial loosely to the resonant circuit. That gives a stepped up voltage and does not restrict the upper tuning frequency. Cuddlyable3 (talk) 13:27, 15 June 2009 (UTC)

Resistance is one of the factors that makes up impedance, so it is an oxymoron to state that it has high resistance but low impedance. As for the transformer, yes, it is passing an audio modulated RF carrier. Crystal radios never strip out the carrier, it goes straight to the earpeice. CrispMuncher (talk) 21:59, 15 June 2009 (UTC)

A capacitance C has the impedance

${\tilde {Z}}_{\text{capacitor}}=-j{\frac {1}{\omega C}}.$

Thus impedance is a complex (vector) quantity and one may equate it with resistance only in a DC circuit. This is basic AC circuit theory and the suggestion that I have expressed an oxymoron is wrong. Most crystal radios have a reservoir capacitor following the detector. It's purpose is to strip carrier frequency and pass audio. Thus it is wrong to claim that crystal radios always send carrier to the earpiece, although that mode is possible with reduced efficiency. Cuddlyable3 (talk) 10:33, 16 June 2009 (UTC)

No, that is the reactance of the capacitor. Impedance is the sum total of the DC resistance and any inductive and capacitive reactances. As electrical impedance states "It is important to realize that resistance and reactance are not individually significant; together they determine the magnitude and phase of the impedance..." CrispMuncher (talk) 17:59, 16 June 2009 (UTC)

If you have found Electrical impedance then please read the section called Deriving the device specific impedances. There you will find the equation I quoted. Capacitive reactance is given by

$\mathrm {X} _{C}=-{\frac {1}{\omega C}}$'

If there were resistance in parallel with the aerial then Electrical impedance also shows how to calculate its overall impedance. However in the case of the simple aerial we can say it has no (0 ohm) resistance in series or infinite resistance in parallel; these statements are equivalent and mean that resistance plays no rôle in the aerial's impedance. BTW this is for an aerial that is small relative to the received wavelength. Cuddlyable3 (talk) 06:52, 17 June 2009 (UTC)

If you wish to discuss these points further I suggest placing these posts under a different heading than "Powrr source". Cuddlyable3 (talk) 06:52, 17 June 2009 (UTC)

Sorry to respond to such an old comment but I couldn't let that drop: CrispMuncher has this correct on both counts. Impedance IS generally defined in the broader sense used by CrispMuncher. The two equations for reactance are equivalent and not understanding why suggests that it is you that needs to do a little more reading up on this. Better to do that than suggesting ignorance on the part of someone who clearly has a deeper understanding of he material. 87.112.122.73 (talk) 20:26, 20 August 2011 (UTC).

Interesting discussion; I might add a couple of comments. The power is enough to drive phones; it takes only a few nanowatts to produce audible sound in efficient phones. In theory and in practice, this is easily produced in an antenna by MW and HF radio waves from stations thousands of miles away, no need for quantum mechanics here. It does not need to power a larger load than the radio waves can manage. (I have personally made the calculations and I have made the measurements to prove it. It is a problem above VHF, but then, xtal sets do not work well there.) Inverted L antennas with length around an eighth to quarter wavelength do not have incredibly high impedances, they are quite easy to match, thats why it works so well.

A good discussion is involved for this page, but briefly: In weak signal mode, the phones are not actually the load on the tank, the diode is. Furthermore, the diode impedance is the source impedance for the phones, not the tank. We match the tank to the diode, and the phones to the diode. The antenna coupling circuitry, including the RF transformer actually matches the real part of the antenna radiation resistance, ground resistance and loss resistance to the diode. John (talk) 04:28, 20 June 2009 (UTC)