Talk:Superheterodyne receiver

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What are the disadvantages of this type of receiver?

It does not have any significant disadvantages and that is why it is so popular but one could cite i) its relative complexity and larger component count (typically one needs three transistors for a superhet up to the aduio amplifier stages, and only one for a super-regenerative receiver ii) susceptibility to image frequencies (the receiver will pick up another signal separated from the intended input signal by twice the IF frequency and lying on the other side of the local oscillator frequency. This problem can largely be eliminated by using a tuned front end to suit the desired band of frequencies iii) a superhet can be sensitive to adjacent channel interference and other forms of interference. Use of a double-tuned superhet (eg radio control receivers) helps to reduce the superhet's noise susceptibility

Also mention that the local oscillator signal is a source of spurious emissions and can sometimes be detected a long way from the receiver. The practical consequence of this can be seen by anyone who's ever experienced a radar detector detector at work. The mixer stage can sometimes be overloaded by strong out-of-band signals which can produce interference. These disadvantages should be written up for the article. --Wtshymanski 14:39, 17 November 2005 (UTC)

Not to mention radar detector detectors that detect IF leakage from detectors. Gah4 (talk) 11:56, 20 February 2021 (UTC)

Subheterodyne mixing

A good example can be found at http://www.patentstorm.us/patents/5461426.html
In particular the 11^th paragraph of the DETAILED DESCRIPTION section.

The desired output signal is at 10.74 MHz (see 9^th paragraph). Bob K 00:31, 17 November 2005 (UTC)

The 11^th paragraph describes two techniques: "... using a lowpass FIR digital filter and a 10.84 MHz oscillator to carry out a superheterodyne ... rather than the bandpass FIR digital filter and the 10.64 MHz oscillator to carry out the subheterodyne...".

I'd never seen this "subhetrodyne" term before yesterday on the Wikipedia and I've read a *lot* about receivers in the last 30+ years. Since the term is *not* standard in the industry (for example, its not in IEEE 100), I think it's a neologism and should not be propagated here. It's also wrong, since the "super" means "supersonic", i.e., above audible, intermediate frequency, and does not describe the relationship of the local oscillator to the incoming signal. The cited patent pages do not use what I believe to be is standard vocabulary. --Wtshymanski 14:35, 17 November 2005 (UTC)

---

Would everyone please sign your comments with four tildes i.e. ~~~~ DV8 2XL 22:47, 16 November 2005 (UTC)

I believe the terms are upper LO and lower LO.^[1]

References

1. "Why it is preferred to have local oscillator frequency larger than carrier frequency in superheterodyne receiver?". electronics.stackexchange.com. Retrieved 4 February 2019.

Double tuned

• Superheterodyne receivers usually contain double tuned circuits (sets of two loosely coupled circuits) as filters in IF receiver - this is because such a filter has almost flat band instead a peak - filtering a signal through many "peak" filters would severely distort it. Seems these tuned circuits are not even mentioned on English Wikipedia, and I am not sure what is their preferred name - is it the "double tuned circuits", or another one?

• There were many different AM IF frequencies used after II World War: in Poland there is 465 kHz standard, in GDR most receivers has 468 kHz, but there were also 440 kHz (Beethoven) and 473 kHz (Undine EAW 7695E) - from engineer's handbook (Poradnik radio- i teleelektryka, PWT Warszawa 1959, Poland) where 42 receivers are briefly described ... which countries used the 455 kHz said here?

• Except image frequency receiving, I recall two other problems these receivers have: larger noise (because mixer both produced own noise due to "sampling", and it catched noise at image frequency produced in RF amplifier), and tuning both input RF filter and oscillator circuit in a way that their frequencies keep constant difference (there was e.g. three-point tuning - for three RF-s of a band the RF filter and oscillator were tuned correctly, for any other RF there was some mismatch). And design of such a receiver requires a lot of work - it is not a receiver an amateur can build in a day or two, unless he has detailed information how to tune it correctly; it is suitable to design such a receiver for mass-production, when high cost of design has little effect on price.

• In "Overview" (near end): "The oscillator also shifts..." - I think the mixer shifts, not the oscilator.

JerzyTarasiuk 19:14, 10 November 2007 (UTC)

---

As far as I know, the real inventor of the superhet was Lucien Levy, french ingenieur diplomed from the Ecole Supérieure de Physique et Chimie de Paris. The very first patent concerning the superhet has been issued in August 1917, one year before E.H. Armstrong's work (patent number 493660). This patent was completed one year after (describing not only the principle, but the schematic of a superhet receiver) the first of october 1918, patent n°506297. —Preceding unsigned comment added by 62.147.135.142 (talk) 09:13, 18 December 2007 (UTC)

For television receivers, the IF amplifiers have to be flat for the whole bandwidth, maybe 4.5MHz, of the video signal. That is much wider than for AM or FM radio. Gah4 (talk) 19:41, 30 April 2018 (UTC)

Actually, I just remembered that this is wrong. (Well, some days ago ...) For analog TV, the IF has to undo the effects of vestigial sideband modulation, such that the result is flat from the video input to the modulator. The response, then, is two flat parts with a transition in between. Gah4 (talk) 23:15, 4 February 2019 (UTC)

With regards requestphoto

Are these images of any use to the article?

A 5-tubes superhet receiver made in Japan about 1955.

Two section variable capacitor, used in superhet receiver

If so please cut and paste to article page. Traveler100 (talk) 06:05, 24 August 2008 (UTC)

• Done, thanks! Tim Pierce (talk) 12:01, 16 April 2009 (UTC)

Edited History Section

Would whoever recently pasted large lumps of technical explanation into the text please stop doing that. The History section does not need to go into such extreme detail; you're simply making it harder to follow. There are places for that further down. Ultramince (talk) 02:20, 26 February 2009 (UTC)

455 kHz for medium-wave AM broadcast receivers

This was a standard frequency long before ceramic resonators were common - for example, the RCA "Radiotron Designer's Handbook 3rd Edition" says frequencies in the range 450-460 kHz were common, and that edition is from 1942. --Wtshymanski (talk) 17:40, 1 September 2009 (UTC)

Why super ??

Why superheterodyne receiver called super........... —Preceding unsigned comment added by 58.68.8.190 (talk) 12:40, 7 November 2009 (UTC)

'Cause it's super. More seriously, because the heterodyne (beat) frequency is above (super) the audible range. Unlike an earlier version of the detection technique, where the heterodyning oscillator is on the same frequency as the input and beats it down directly to audio. This works, but has drawbacks too numerous to describe here. Hmm, does this need to be more explicitly described ? --Wtshymanski (talk) 22:17, 20 November 2009 (UTC)

That explanation is commonly given, and is completely wrong! Superheterodyne is a contraction of "Supersonic Heterodyne". Before WWII "Supersonic" meant "having a frequency beyond the range of Human hearing", so a Supersonic Heterodyne simply meant one where the characteristic whistle was too high in frequency for a person to hear. However since WWII the term "supersonic" has come to mean: "something that travels faster than sound" (such as a Supersonic Aircraft). The original meaning of "supersonic" has now been generally replaced by the term "Ultrasonic". — Preceding unsigned comment added by Elekas (talk • contribs) 02:16, 1 March 2012 (UTC)

Until now, I always thought it was because Armstrong previously build heterodyne receivers with oscillating amplifiers. I don't know the exact details, though. So the new invention was super (better) than the old one. Now I am not sure. Gah4 (talk) 19:44, 30 April 2018 (UTC)

When is intermediate frequency higher than carrier?

Ultramince recently added language to the introduction indicating that intermediate frequency can be lower or higher than the carrier. I've simplified the language but I'd like to see a reference showing where this technique is used. I've added a citation request tag to the one sentence in the article that mentions this. --Kvng (talk) 15:03, 20 November 2009 (UTC)

Check out the ARRL handbook or, gosh, just about anything that talks about superhets. It's a stone-standard technique. A scanner (radio) will often up-convert, because if you have a wide-band RF front end it contributes little to image rejection - by converting to a higher IF than the input, images are placed so far out that the IF filters can handle it. Often done in general-coverage shortwave radios, for example the DX 440 I have uses a first IF around 55 MHz, then converts down again before demodulation. AM broadcast recievers get away with down converting to 455 kHz because that's still fairly high compared to the input signal, and there's always a tuned circuit ahead of the converter stage. --Wtshymanski (talk) 22:12, 20 November 2009 (UTC)

My problem is that higher IFs are mentioned very briefly in the article with no elaboration as to why this technique would be useful. I now appreciate that a receiver covering a wide frequency range (e.g. a scanner) must have a wide-band front end and therefore has a problem rejecting input that would land on top of a lower IF. I'd be happy to edit the article to include this information. Are there any other cases where a higher IF is useful? Also I don't have a copy of the AARL handbook so can't pull up citation. --Kvng (talk) 16:45, 22 November 2009 (UTC)

I don't have specialist literature on design of receivers at hand, either, and the principle is so general it only gets mentioned in passing in the more general references I've got. The 1991 ARRL handbook discusses IF choice around page 12-26, and says that a 455 kHz If isn't very useful above about 7 MHZ because of the image problem. "Solid state design for the radio amateur", another ARRL book, also describes IF choice and the different approaches used in hf ham gear from the 40's to the '70s. The CRC Press "Electrical Engineering Handbook" edited by R. C. Dorf just blithely says a superheterodyne converts up or down to an IF and then skips off into the bushes, not describing why you'd go either way. I think it's sufficent for encyclopedia purposes to mention that the if may be below...or above...the signal frequency, and refer to the textbooks for the gory details of why you would pick different ifs. A quick spelunk through my confused files has not turned up my DX 440 manual yet, which is a digital tuning general coverage SW radio. It's not unique in up-converting. --Wtshymanski (talk) 17:26, 22 November 2009 (UTC)

Finding my scanned manuals, for interest, the Radio Shack DX 440 (also Sangean 803) has a first IF of 55.845 MHz and tunes 150 kHz to 30 MHZ, the Radio Shack PRO 2006 scanner has a first IF around 610 MHZ, (tuning from 25 MHZ to about 1300 MHZ in several bands) and the Radio Shack PRO-2050 has a first IF of around 380 MHZ ( again, tuning several VHF and UHF bands). --Wtshymanski (talk) 04:31, 23 November 2009 (UTC)

"Are there any other cases where a higher IF is useful?"

Higher frequencies require smaller usually lower cost components. Look up switching power supplies for an example. MMICs allow for an LNA, balanced mixer, and filters in a single chip, but only at microwave frequencies (needs updating as to lower frequency bounds).

Most SDR chips have a lower frequency limit, of 30, 50, or 70 MHz, direct conversion is either not possible, or degraded for reception below these frequencies; By using a higher IF these signals can be decoded. (Ham-it-up for RTL-SDR).

Bandwidth when combined with interference can be an issue, when powerful external signals, high power AM, FM, TV, Time(WWV) or shortwave transmitters, fall within the IF range. Additional shielding would be required adding cost to the design. Loss through free-space increases with frequency making interference less likely in wider bandwidth applications.

The main drawback to higher IF frequencies is the lower-loss sharp-cutoff crystal-lattice filters are not available at the higher frequencies, requiring high loss saw filters (lower sensitivity, increased SNR due to amplifiers required) or large helical or can filter designs for good image rejection and selectivity.

Many modern triple-hetrodyne designs include a stage above the carrier frequency. The first stage, of 3, of the Yaesu 991A (https://www.yaesu.com/downloadFile.cfm?FileID=8711&FileCatID=156&FileName=LEAFLET%5FFT%2D991%5FENG.pdf&FileContentType=application%2Fpdf) for SSB/CW/AM modes is 69.450 MHz/ 9MHz/ 450kHZ . This is an up-conversion for all HF/50 MHz bands.

I would venture to say the most modern ham radios with a pan-adapter(SDR) integrated has an IF stage above the carrier frequency. 65.191.245.218 (talk) 19:31, 12 June 2022 (UTC)

There used to be, maybe still are, various frequency converters. Before cable TV got so fancy, there were devices that would take the whole cable TV band and upshift it to the UHF TV band. In that case, the output of to box is the first IF, and input to a UHF TV tuner, which then converts to the usual TV IF. Well, not the usual IF, as it is different for different channels, but it is, in the sense that it gets converted again. Gah4 (talk) 07:26, 11 May 2023 (UTC)

Proposed merge of Intermediate Frequency

There is a template on Intermediate frequency proposing a merge here. I am not so sure this is a good idea, I suggest that the proposer states the case for merger here before anything is done. Also it is normal in proposed mergers to put a template on the proposed target article as well with a link to the same discussion. SpinningSpark 18:18, 29 November 2009 (UTC)

I oppose this merger. Frequency upconversion and downconversion using intermediate frequencies is a common technique in communications engineering, widely used in many devices besides superheterodyne receivers, such as radio transmitters, modems, cable television systems, radio repeaters, microwave radio relays, satellite transponders, fiber optic communication systems, cell phones and cellular base stations, telemetry systems, and microwave test equipment. --Chetvorno^TALK 19:39, 29 November 2009 (UTC)

This does not look like a good idea to me either. The Hetrodyne article would be a better merge destination candidate but I don't support that. I do support some other heterodyne merge proposals --Kvng (talk) 17:51, 30 November 2009 (UTC)

Oppose = the article is about a receiver, not just a circuit module component.Francis E Williams (talk) 16:55, 17 January 2011 (UTC)

OPPOSE. I am sure that there are many articles that overlap enough that they should merge, but I don't believe that this is one. This article should contain enough details about IF to follow the rest of the discussion. The Intermediate frequency article should include details not needed here. The IF section of this article should not be excessively detailed, or excessively simple, compared to other sections. Gah4 (talk) 05:40, 4 February 2019 (UTC)

Duplication of content

The article contains the same informaion in many of its sections, it needs to be restructured slightly and some sections rewritten to clarify what is being said.Francis E Williams (talk) 15:19, 17 January 2011 (UTC)

You'll find the Wikipedia chief editor's Telex and FAX numbers on the home page; using either of these media, you can request the forms to make an editorial change to the article. Please allow 4 to 8 weeks for the submittal to be considered at the next editorial committee meeting. Rememmber, all manuscript submissions must be typed double-spaced, pica font, with a new fresh ribbon on 20 lb paper, on only one side. Please enclose a self-addressed stamped envelope with your submission in case it is rejected by the editorial committee and you want your manuscript back. --Wtshymanski (talk) 15:35, 17 January 2011 (UTC)

Thank you for the information. I have since received a suitable responce via UPS and have uploaded the approved content accordingly. My submission was approved on the basis that it did not remove any content, but was simply re-ordered it into a logical more readable sequence.Francis E Williams (talk) 16:52, 17 January 2011 (UTC)

The joke "They must be in a hurry; they Fedex'd you a FAX machine" is meaningless to today's Twitterati. And 07 57506 was the compnay Telex number, a generation ago when dinosaurs ruled the Earth. --Wtshymanski (talk) 17:26, 17 January 2011 (UTC)

The invention of the 3D printer has been a Godsend here in my village.Francis E Williams (talk) 17:33, 17 January 2011 (UTC)

Which characteristic is amplified in "IF Amplifier" stage?

Which characteristic is amplified in "IF Amplifier" stage? — Preceding unsigned comment added by 122.175.130.247 (talk) 06:05, 2 July 2011 (UTC)

Selectivity.

Wikisc84 (talk) 14:59, 28 November 2012 (UTC)

The IF amplifier has two primary goals.

First, it amplifies the weak signal coming out of the mixer. It is often difficult to obtain gain at RF frequencies; translating the RF frequency to a lower frequency IF eases the problem of obtaining gain. In addition, some stability issues are easier to meet.

Second, the IF amplifier provides selectivity. At a lower IF frequency, a bandpass filter has a lower Q for the same signal bandwidth.

Glrx (talk) 04:56, 11 December 2012 (UTC)

Local oscillator radiation to detect receivers

I don't know if the BBC uses LO radiation, but Britain knew coded instructions were being sent to spies, so it tried to find those listening by searching for oscillator radiation (in the 1950s?). The reported search was unsuccessful, but that does not mean it wasn't later refined. I think it was in a book about Britain's anti-spy efforts. The book included a bizarre scheme where plaintext was recovered from the teletype transients that leaked across the coding equipment. I don't recall the author or the title.

In California many years ago, a common carrier hired amateur photographers to take pictures of dish antennas that were capturing forbidden content. A van confirmed that the receiver was active.

Glrx (talk) 22:48, 2 August 2012 (UTC)

I worked on systems that successfully detected radio receivers via their LO radiation. As part of the research we investigated "TV Detector Vans" and found the idea that they caught non-licence-holders by detecting LO leakage to be a complete myth.

Wikisc84 (talk) 14:55, 28 November 2012 (UTC)

I could easily believe detector vans would have trouble with today's TV sets, and I could believe detector vans would have problems with old VHF tuners. I expect those receivers would use RF amplifiers. However, old UHF tuners were just diode mixers and could have significant LO leakage. Glrx (talk) 05:04, 11 December 2012 (UTC)

As well as I know it, UHF station frequencies are assigned to avoid image problems, and also leaking LO problems. Gah4 (talk) 19:49, 30 April 2018 (UTC)

This section has nothing to do with image frequencies or leaking LO interfering with nearby sets. It's about LO leakage being used to detect receivers. Glrx (talk) 00:18, 1 May 2018 (UTC)

If there is enough LO leakage to cause problems in other receivers, then there is probably also enough to detect otherwise. Gah4 (talk) 00:41, 1 May 2018 (UTC)

TRF/Neutrodyne was easier to use than superhet?

In the History section, paragraphs about why superhet didn't catch on immediately in the consumer market claim that one reason was that the superhet required greater technical skill than tuned receivers. How can it be easier to use, when you have to separately tune multiple stages to the station frequency? That text needs to expand about what it is that made early superhet receivers hard to use. Because, clearly, later superhet receivers are such that anyone can use them without technical skill: just turn a knob until you hear a station. Did the early superhet units require the user to tune two or more circuits? Like the local oscillator and a filter for the incoming signal? 24.85.131.247 (talk) 05:26, 3 February 2013 (UTC)

OK, I understand everything.

• Tuned radio frequency receivers put the incoming signal through numerous stages which tried to amplify the band around the station frequency and suppress other frequencies. The purified result is then subject to detection to extract the signal. The problem with this is that three or more stages need to be tuned to change a station.
• Superhet essentially replaced a whole section of the TRF with fixed-frequency circuits. However, it did not entirely eliminate the tuning of multiple stages. Superhet still requires the RF and LO stages to be tuned in step. Yet this appears simpler than the operation of a TRF: tuning at most two things in step is easier than three or more. See here: http://www.sentex.ca/~mec1995/gadgets/pll/pll.html "However, because of the number of tuned stages in a superheterodyne, a simpler method was desired. In 1932, a team of British scientists experimented with a method to surpass the superheterodyne. This new type receiver, called the homodyne and later renamed to synchrodyne, first consisted of a local oscillator, a mixer, and an audio amplifier. "
• The new method was to use heterodyning to go directly from the carrier frequency to baseband, skipping the intermediate frequency: Synchrodine (direct-conversion receiver).
• Superheterodyne reigned for a few decades because Synchrodyne required a complex phase-locked-loop circuit which didn't become economic until integrated circuits came along. The reason it needs a PLL is because direct conversion does not use a rectifier based envelope detector to extract the amplitude-modulated signal. Therefore a very accurate tuning is required in the local oscillator which dynamically tracks the frequency of the station.

It might be something worth incorporating into the History section. 24.85.131.247 (talk) 19:43, 3 February 2013 (UTC)

Separate/combined mixer/oscillator.

Yes, conceptually the local oscillator and mixer are two separate things, but every practical Am broadcast band receiver that I have ever worked on, or even just seen a circuit diagram for, had the one transistor being a combination mixer oscillator. 121.217.52.34 (talk) 07:40, 10 June 2013 (UTC)

Wax potting

While I don't doubt that a little security might have been a consideration, a larger one is illustrated by the...um, illustration. Wax potting prevents corrosion in wet and salt environments. The wax melts out quite easily, and is useless to prevent commercial espionage. Anmccaff (talk) 17:22, 22 February 2016 (UTC)

Frequency spectrum diagram

How a superheterodyne works. The incoming radio signal (RF) from the antenna consists of a carrier frequency (dark blue) with sidebands (light blue) on either side containing the modulation. Mixing this with the local oscillator signal (LO), creates a heterodyne intermediate frequency (IF) at the difference between these frequencies. This is bandpass filtered in the IF amplifier, and the demodulator extracts the modulation (M). Because the Image frequency when mixed with the LO also creates a signal at the IF, the RF image rejection filter on the input of the receiver filters out any radio signal at the image frequency.

@Glrx: what is your objection to the diagram? --Chetvorno^TALK 20:29, 31 October 2016 (UTC)

It's too busy and confusing. I've inserted the diagram and caption as they were in the article. It's a figure where one must already understand what is going on in order to appreciate it; I don't think it is clear to one who is learning. The diagram plots multiple signals (baseband, IF, LO, RF) on the same axis; that's confusing. You know how the signals are used, so you can separate them out in your mind. That's not the case with someone who does not know what is going on. Is the LO received along with the image and RF? LO and RF convolve to produce a result, but they are not present in the same signal. Why is the image a dashed CW frequency more reminiscent of the LO and not looking like another, undesired, station? Is the image another oscillator? The figure has multiple operations described without separating them. Consider plotting separate signals that are tied to the signals in the block diagram. In addition, the figure implies a specialized source (DSB) in a general situation; what about CW, SSB, and FM? The figure focuses on the artifact issue (image rejection) while ignoring primary asset of high selectivity. The heterodyne didn't leave any work for the IF filter (only one station needs to be filtered). Glrx (talk) 21:55, 31 October 2016 (UTC)

Inventor - What About Schottky?

Reading ^[1] it seems that Walter Schottky should be mentioned as well, any thoughts on this? Or has this been discussed earlier? Cyberroach (talk) 24 June 2017 (UTC) — Preceding unsigned comment added by 50.47.43.69 (talk)

References

1. http://ethw.org/Superheterodyne_Receiver

Article text in the EL section

Not sure why a large amount of martial was added to the EL section, seems way beyond MOS. If its sub-material from the same site, link only the site (WP:ELPOINTS #4). If its a mass of martial on an alternative view to correct a "poorly sourced and skewed" history section, well, the EL section is not the place where you do that (WP:ELPOV). If this is material from reliable sources then it should be added to the "History", not the EL section. Fountains of Bryn Mawr (talk) 22:56, 4 July 2017 (UTC)

so employing a higher IF frequency fIF increases the receiver's image rejection without requiring additional selectivity in the RF stage.

so employing a higher IF frequency fIF increases the receiver's image rejection without requiring additional selectivity in the RF stage. has a dubious/discuss. It seems somewhat obvious that it is easier to filter out signals that are farther apart. In some cases, though, you can be unlucky with image frequencies. Frequency assignments are often made considering the problems with image frequency reception. Gah4 (talk) 19:52, 30 April 2018 (UTC)

I now removed: ^{[dubious – discuss]} As above, with a given RF stage filter, a higher LO frequency reduces image problems. That is, the image frequency will be more attenuated by a given filter. Gah4 (talk) 07:29, 1 August 2018 (UTC)

Do you have a source for what you think "seems somewhat obvious"? The claim in the article is unsourced, too. It's not the hertz difference but the octave difference that counts. And don't think about just bandpass filters. Glrx (talk) 14:29, 1 August 2018 (UTC)

Sharper/narrower filters are harder to make, that is filter theory 101. So more octaves away means easier filtering. Gah4 (talk) 05:23, 6 August 2018 (UTC)

Filter magnitude goes down by x*20dB/decade though, with x being filter order. This means that by just increasing all frequencies in the circuit by tenfold, you gain nothing in 'easy filtering'. That's because (f1=cutoff freq, f2=undesired freq) filter attenuation will still be A=-20*log10(f2/f1), hence 10*f2 and 10*f1 just cancels out. It's not absolute spacing (which becomes larger when increasing overall frequencies) but relative spacing (which stays the same) that counts.2A02:1810:527:3300:C8F4:F781:5A09:6C01 (talk) 10:01, 24 December 2020 (UTC)Helsen

But you're not increasing all frequencies. An AM broadcast band receiver with a 455 kHz IF will have better image rejection than a receiver with a 200 kHz IF, with the same number of active stages and same IF filter design, for receiving the same (over-the-air) frequency. --Wtshymanski (talk) 07:16, 26 December 2020 (UTC)

"so employing a higher IF frequency IF increases the receiver's image rejection without requiring additional selectivity in the RF stage", This is the cost of sensitivity. Every choice is a balance between selectivity and sensitivity. My Boefang radio has great sensitivity, but with that sensitivity, comes random noises that un-squelch the radio. My Icom and Yeasu radios fail to decode the same signals, but when they do, the audio is much better.

There is no panacea. 65.191.245.218 (talk) 21:53, 12 June 2022 (UTC)

Suggest merge January 2019

Intermediate-Frequency (IF) amplifier should be merged with this article with any unique content added.; As a stage of a superhet receiver, the amplifier has little or no independent notability and would always be discussed in context of a receiver. This article has more description of the IF amp than the proposed merge source anyway, so there may be very little that needs to be added here. Discussing all the stages in one place gives a more comprhensive overview of the topic and doesn't waste the reader's time clicking on links that give no additional useful information. --Wtshymanski (talk) 20:26, 30 January 2019 (UTC)

As with Intermediate frequency, I thought that the more theoretical descriptions would go here, and more practical ones in Intermediate-Frequency (IF) amplifier. As this one is already pretty long (are there suggested guidelines for article size?) some details might move out of this one. It seems to me that readers often would be more interested in the theory, or more interested in practical descriptions, (even historical ones), so the separation would be useful. Details like the tuning of an IF strip for a vestigial sideband receiver aren't here, and might be too specific to go here. (The response has to correct for the different amplitude of the two and one sideband frequencies, after demodulation.) Details on the pentagrid converter are also more practical than theoretical, for example. Gah4 (talk) 02:22, 31 January 2019 (UTC)

The nutshell description at Wikipedia:Article_size says "Neither too long nor too short" which is such a Wikipedia thing to say. The numeric guideline is 4000 to 7000 words of readable prose. This article is just under 5000, so it's creeping up on the limit ( but probably needs editing which would bring it back down again). Agree, if Intermediate-Frequency (IF) amplifier persists it would be the place to put the finer details, with a good overview left here - but how much more detail can you put into an encyclopedia article before it becomes a how-to guide or a textbook? --Wtshymanski (talk) 16:05, 31 January 2019 (UTC)

Support, for now - @Gah4: you made some good points, but I think the amount of information does not justify a separate article yet. When this article becomes larger it can be split off. We also have Radio receiver design for this content. Vacuum tubes, pentagrid converters, double-tuned transformers, and "aligning" an IF strip are mainly historical subjects which could go in History of radio receivers. Modern receivers use ICs and crystal or ceramic filters, and increasingly digital IF signal processing. These are the subjects that really need more coverage. --Chetvorno^TALK 20:35, 31 January 2019 (UTC)

The section names in the "Principle of operation" section should follow standard superhet terminology; the "Amplifier" section should be renamed "IF amplifier". There are several amplifiers in a superheterodyne. --Chetvorno^TALK 20:35, 31 January 2019 (UTC)

• Oppose for now. IF amplification is more general than superhets, more general than televisions and audio radios. I worked with IF amps in satellite data systems and such back when I was into that. I expect some appropriate expansion could make this a much better article (here, for example, shows use of IF amps in a digital beamsteering radar system). I fixed the name and lead a bit. Dicklyon (talk) 02:29, 4 February 2019 (UTC)

• Oppose since I didn't say it above. Combining them, and then separating again, is a lot of unneeded work. If that work went into improving the articles, the result would be better for both. Gah4 (talk) 05:48, 4 February 2019 (UTC)

• Oppose. I'm sympathetic to the merge because the term IF amplifier is closely associated with a superhet; you do not have an intermediate frequency without a frequency conversion. That said, I think electronics texts would devote entire chapters to IF amplifiers. Technically, they are narrowband, high-gain, amplifiers. High gain means stability problems. A synonym is IF strip, and that came from the component layout wanting the input and output to have large separation to reduce coupling. Neutralization would be used to increase stability. Sometimes unilateralization would be used to increase stability and make the tuning sections independent. I remember reading about the design of IF transformers: the tank L and C values would be chosen, and then there would be an impedance transformation from the device output to the entire tank, and then a second impedance transformation to match the input of the next stage. Then there was either AGC (AM) or limiting (FM) applied to each stage. When ICs came along, AGC and limiting became easy; IC IF amps would have signal level outputs. IF filters shifted from transformers to ceramic resonators and SAW devices. There should be plenty of material for an article on IF amplifiers that should not be covered here. For the purposes of describing the superhet, one need only have a fixed-tuned, narrowband, high-gain amplifier. Glrx (talk) 19:11, 4 February 2019 (UTC)

  Radio Engineers' Handbook, Terman, 1943, has a large section on tuned amplifiers. Page 434, "Such amplifiers are used to amplify signal frequency voltages in radio receivers, in which case they are referred to as tuned radio-frequency amplifiers, and also to amplify intermediate-frequency voltages in superheterodyne receivers." Glrx (talk) 22:13, 4 February 2019 (UTC)

  Basic Theory and Application of Transistors (Army Technical Manual), 1959, devotes a chapter to tuned amplifiers. Glrx (talk) 22:05, 4 February 2019 (UTC)

  GE Transistor Manual, 1964, page 286. "The input and output are coupled by means of tuned IF transformers. … The collector of the transistor is connected to a tap on the output transformer to provide proper matching for the transistor and also to make the performance of the stage relatively independent of variations between transistors of the same type. With a rate-grown NPN transistor such as the 2N293, it is unnecessary to use neutralization to obtain a stable IF amplifier. With PNP alloy transistors, it is necessary to use neutralization to obtain a stable amplifier and the neutralization capacitor depends on the collector capacitance of the transistor." The section goes on to address implementing AVG (AGC) with emitter current reduction and an auxiliary diode AVC system. Glrx (talk) 21:33, 4 February 2019 (UTC)

  Electronic Engineers' Handbook, Fink, 1975, page 21-56, "The [FM] if amplifier must provide sufficient gain for the noise generated by the rf amplifier to saturate the limiting stages fully if the benefits of wide-band FM are to be obtained at low signal levels. … One of the most important characteristics of the if amplifier is phase linearity, since envelope-delay distortion in the passband is a principal cause of distortion in FM receivers." Glrx (talk) 21:52, 4 February 2019 (UTC)

I believe alloy transistors means Germanium, so some years ago. But yes, I believe that there is enough for the article. I don't know how fast it will be written, though. Gah4 (talk) 23:21, 4 February 2019 (UTC)

although this stage is often omitted

Regarding an RF amplifier before the mixer, the article says: although this stage is often omitted. How often? Since there are many uses for radios now, many of which are digital, the best way to build them is often different than from analog days. I suspect that there are many more WiFi devices than AM/FM radios, which might also affect the often. Maybe this just needs a little more explanation. Gah4 (talk) 15:13, 15 July 2019 (UTC)

According to Electronics for Electricians and Engineers, "The RF stage is omitted for AM radios, and some FM radios use an untuned RF stage...". I can find quite a few other sources saying similar things (although not so specific as an AM/FM split). It certainly seems to be true for pre-digital radios. Valve Radio and Audio Repair Handbook also has something interesting to say on "midget" valve receivers RF stage: "These were sometimes employed, possibly more as a sales feature rather than for their actual performance. There was seldom room or the inclination to fit a three-gang tuning condenser..." SpinningSpark 17:01, 18 July 2019 (UTC)

It seems unlikely we'll find a source about how often it's omitted. Some sources like this 1950 article show diagrams without it. I think that esp. in AM radios it was usually omitted because there would often be signals at the antenna much bigger than the signal you want, and a passive path to the first IF filter was needed to keep from contaminating your signal with IM distortion from other channels; same for FM radio, I would think, though it's more tolerant of interference from IM distortion. After some filtering, some amplification is order, with less stringent linearity requirement. I suspect that's still the case in modern WiFi and such, but I don't really know. Dicklyon (talk) 17:21, 18 July 2019 (UTC)

I thought the usual reason was to reduce LO leakage out the antenna. As I have the service manual for the TU-417 nearby. (I still have the tuner, but don't use it.) It seems to have a JFET RF amplifier on the FM side, and as noted, three-gang tuning capacitor. The AM section is inside an HA1197 IC, where the data sheet doesn't make it so obvious what it does inside. Is there a WP rule on how often something should be to call it often? Gah4 (talk) 23:25, 18 July 2019 (UTC)

It is a noise figure issue. If the application requires a low noise figure, then an RF amplifier can be a good thing. A diode mixer will have about 6 dB of conversion loss. Without an RF amplifier before the mixer, that 6 dB will add to the noise figure. For LF, MF, and HF, there can be enough atmospheric and man-made noise that a 6 dB conversion loss does not hurt: the loss does not hurt the system's SNR. Rohde & Schwarz ELF-070 VLF/HF receiver does not have an RF amplifier. At HF, the noise starts quieting down and at VHF there is little noise. So AM broadcast radios do not need good noise figures; FM radios can make use of good noise figures. VHF and UHF data receivers will want good noise figures because it minimizes data errors and maximizes transmission distance. Garage door receivers may be UHF, but they only want to listen to nearby transmitters, so a high noise figure can be a feature.

LO leakage could be an issue for AM receivers with low IFs, but I'm not sure that is a big issue now. In the early days of radio, the first stage of a cheap radio was a converter, so you were connecting an oscillator to an antenna. Modern designs can have a separate oscillator with a mixer that has reasonable isolation. Glrx (talk) 23:37, 18 July 2019 (UTC)

I think I remember years ago, knowing about the JFET amplifier, having both low noise, and also enough linearity over the region needed in the case of large, nearby signals. I still don't know about the WP meaning of often, though. Weighted over all receivers, or all receiver models? Gah4 (talk) 11:31, 19 July 2019 (UTC)

tuned amplifier

Regarding a recent edit from IF amplifier to IF filter, some might mention tuned amplifier. Also, somewhere there might be indication of the design of IF amplifiers flat over the IF bandwidth, and dropping somewhat fast outside. This is especially important for TV, with the larger bandwidth. Gah4 (talk) 14:52, 20 November 2019 (UTC)

potentially below radio frequency

Since radio frequency goes down to at least 60kHz (WWVB), and for submarine communication down to 7Hz, how do we know what is potentially below radio frequency? Gah4 (talk) 00:45, 22 May 2020 (UTC)

Not always below the radio frequency. I, and probably the vast majority of owners of AM radio sets in my part of the world, own a radio set where the IF is higher in frequency than the received radio signal. This will be true for any set capable of receiving the long wave band. For instance: BBC Radio four broadcasts on 198 kHz, but the standard IF of receivers that receive this signal is 455 kHz. RFenergy (talk) 12:26, 23 May 2020 (UTC)

DC is below all RF. RF is any propagated AC waveform, the reason audio(100Hz to 3KHz) across a wire doesn't transmit *much* is due to wire length, given that antenna efficiency directly correlates with aperture size and wavelength.

At 60Hz, the wavelength is over 3 thousand miles, this is why the US power grid contributes minor noise to the RF spectrum.(Real power loss due to EM radiation is taken into consideration in designs where capacitors are used to ensure phase vs current consistency, thus nullifying emissions.)

The real question is what is above RF. Light is of the wave type Electromagnetic; Where power increases for each electron ring traversed. Then the question becomes is there a limit to the energy in X-rays and higher frequencies... Hint, we would all be dead without limits. 65.191.245.218 (talk) 21:08, 12 June 2022 (UTC)

It seems that amateur radio goes up to 250GHz: Amateur radio frequency_allocations. The redefinition of the meter in (about) 1986 came after optical frequency counting, counting the difference (beat) between two laser beams. Gah4 (talk) 00:27, 13 June 2022 (UTC)

modern receiver on a chip

The article mentions modern receivers using software. I am not so convinced, though I suspect it is more the mistake in SDR itself. If you are building a receiver for one band, which isn't likely to change, there is no need to do it in software. Just build the digital logic for the needed operation. Software is convenient when it needs to change. In any case, I just learned about the GS1299 which is, pretty much, a single chip FM stereo receiver. There is a simple LC filter on the input, probably to filter out things like AM radio. There is a 32768Hz crystal, and everything else is inside. I tried to find the patent for it, to get more details, but couldn't find it. I built a kit FM radio that uses it. (Almost finished.) Presumably it uses PLL frequency multipliers to generate the needed frequencies. You don't need software to build digital filters, just blocks of digital logic, multipliers and adders and such. If anyone knows of other such chips, it would be interesting to know about them. Gah4 (talk) 12:09, 20 February 2021 (UTC)

"there is no need to do it in software" Why not?

The same argument was made about using sound card chips for modems over 20 years ago. 28.8 Kbs per second was the fastest at the time, 33.6 Kbs modems were the first to embrace the technology, thus allowing a software change enable 56 Kbs when available.

When technology moves to DAB+ or HD-Radio(once the patents expire) only, your single chip solution becomes obsolete.

"In any case, I just learned about": Many chip suppliers have been providing single chip FM receivers for many years, this is nothing new, and this discussion has nothing to do with the topic at hand. 65.191.245.218 (talk) 20:07, 12 June 2022 (UTC)

I haven't followed them quite close enough, but I believe that traditional analog radio receivers have been in ICs for years, though with some external LC filters and such. That is, usual local oscillator, mixer, IF amplifier(s), and demodulators. Maybe fully digital is more recent. (I believe it still has an analog mixer, but with digital filtering where needed.) Gah4 (talk) 01:22, 5 January 2023 (UTC)

I built "digital radios" in the 1970s, with TTL chips doing digital filtering, and with analog mixers and such. Here is a report on the first bit I delivered; the analog "baseband mixer" or "integrate-and-dump" circuit, was problematic, as discussed in the report. Not my design, I just had to build and deliver it. I had also made an AM receiver with digital PLL frequency multiplier as an undergrad project, 1973. Dicklyon (talk) 02:40, 5 January 2023 (UTC)

Also, before any GPS satellites were up, I worked on a digital GPS receiver that was so small and so light that it could be carried on the back of one soldier! Dicklyon (talk) 02:42, 5 January 2023 (UTC)

But not for $0.10, which seems to be the price for the GS1299. Gah4 (talk) 14:02, 5 January 2023 (UTC)

SDR with analog mixers

There is a recent edit, and edit summary, regarding SDR and direct conversion. As well as I know, there are a few different ways to build SDR. One is to digitally, (software controlled) generate a LO, then input that into the usual analog mixer, and digitize the output. That is pretty much how the GS1299 described above works. The data sheet only says "low IF", and I don't find it on a patent, either. I believe it then digitizes the low IF, and digitally demodulates the FM signal. After that, it has to digitally demodulate the FM stereo signal. The only frequency reference is a 32768Hz crystal, from which it generates all the needed frequencies. Some SDR articles suggest directly digitizing the RF. Except at lower frequencies, maybe medium wave AM radio, direct digitizing at RF isn't easy. And digital mixers at VHF or higher is not easy, either. Gah4 (talk) 08:25, 11 May 2023 (UTC)