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 site 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) susceptibity 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 frquencies iii) a superhet can be sensitive to adjacent channel interefrence and other forms of interference. Use of a double-tuned superhet (eg radio control receivers) helps to reduce the superhet's noise susceptibity
- 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)
[edit] subheterodyne mixing
A good example can be found at http://www.patentstorm.us/patents/5461426.html
In particular the 11th paragraph of the DETAILED DESCRIPTION section.
The desired output signal is at 10.74 MHz (see 9th paragraph).
The 11th 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)
Bob K 00:31, 17 November 2005 (UTC)
Would everyone please sign your comments with four tildes i.e. ~~~~ DV8 2XL 22:47, 16 November 2005 (UTC)
[edit] 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 465kHz standard, in GDR most receivers has 468kHz, but there were also 440kHz (Beethoven) and 473kHz (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 455kHz 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)
