Talk:Frequency mixer
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JC wept! As an engineer who uses mixers daily, I wouldn't recognize the article as being related to either a simple, or a pedantic, treatment of mixers. While most of the words written are true, they are irrelevant and uninformative, one would need to be an expert to understand in what sense they are true, a begineer would be hopelessly lost.
What is the purpose of the wiki? Is it to record some words vaguely related to the subject in hand, or is it to inform or educate? It might be easier to dig up any one of a dozen better written tutorials in the back pages of mixer manufacturers' catalogues, many available on the web and just point to them, than to write a new text which doesn't overtly plagerise any of them.
for instance this link http://www.hobbyprojects.com/general_theory/mixer.html is very short, a bit confused (talking about fans beating) BUT the neophyte will come away from it understanding a damned sight more about mixers than from this article, and the expert will recognise it for what it is, a slightly flawed over simplificiation rather than the pile of dingoes kidneys that make up this article.
A mixer does not deal with sine waves, a simplified model of them does. A mixer is a component, not a mathematical equation. Exponential signal expansions convey nothing to somebody who wants to find out what a mixer does.
calms down, thinks, comes back
Perhaps I should be a bit more positive about this, but I'm not up to writing the article at the moment. I will present some definitions and ideas here in talk, and hope that others might consider whether the different approach has merit, and if so whether to modify, replace, rewrite or leave alone the main article. First some comments
The maths in the present article, the diode, exponential stuff etc. This shoudl really be in a seperate artcile entitled "How a non-linear system creates mixing products". It is all correct, just not really applicable to understanding what a "frequency mixer" is, how it's built, why it's used etc.
Proto-article
A frequency mixer is a component, that accepts two electrical signals, and is intended to produce as an output a signal, which has two frequency components, one at the sum of the two input signal frequencies and and one at the difference. Any mixer, whether practical or theoretical, will also produce other unwanted outputs. It is the reduction of these unwanted outputs that consumes most of the engineering time developing better mixers.
A mixer is used where frequencies must be changed for practical processing reasons. In a cell-phone for example, an input radio signal at 2GHz is mixed down to an intermediate frequency (or IF) of 70MHz using a local oscillator (or LO) of 1.93GHz. This is referred to as down-mixing. A transmitter will often use a frequency mixer to up-mix a low IF up to a high RF frequency for transmission.
The practice of mixers frequenctly uses jargon, so RF = radio frequency, usually the highest signal frequency, IF = Intermediate frequency, usually the lowest signal frequency, both relatively low level signals and often modulated, so not a single sine-wave. LO = local oscillator, a high level signal, always a single frequency, but may be sine or square.
There are two pricnciple ways of performing the conversion. The first and mathematically simplest uses a multiplying mixer, usually abrebiated to multiplier, which is linear to the signal at each mixer port and performs the operation z(t) = y(t) * x(t), where x, y and z are the time varying voltages at each port. Multipliers tend to use semiconductor ICs, (496, what manufacturer, AD834 Analog Devices) but they are very noisy so have limited dynamic range. The second, and more commonly used, is a switching mixer, which performs the operation z(t) = y(t) * sign(x(t)), where again x, y and z are the voltages at each port. In the switching mixer, x is the LO.
A switching mixer usually works with diodes, the high level LO serves to switch the diodes rapidly from conducting to non-conducting, producing a switching action for the lower level signals. Recently, MOSFETs have begun to be used as the switching element in switching mixers, offering the advantage of lower power on the LO port.
The type of mixer is determined by the topology of diodes and balancing transformers are involved (a few diagrams here would not go amiss). A single diode mixer is unbalanced, has no isolation between ports, but is very simple and is the mixer of choice when frequencies are so ridiculously high that the only component that can be fabricated and got to work is a single diode (optical, teraHertz etc). Much better is a balanced mixer, which uses transformers and diodes to provide isolation between the ports. A double balanced mixer uses two transformers and four diodes, and provides isolation between all pairs of ports. The single balanced topolgy is sometimes used (one transformer, two diodes) at fairly high frequencies. A triple balanced topolgy (three transformers, 4 or more usually 8 diodes) is gaining popularity with its very good rejection of distortion products.
NeilUK 19:43, 5 June 2006 (UTC)
Thanks NeilUK for writing something practical. --NA 03:03, 10 October 2007 (UTC)
NeilUK, please add your description of a frequency mixer to the wiki and then we'll have an understandable description (for non eng types) and we'll still have the "math" geek description too.64.50.249.202 (talk) 13:21, 1 June 2008 (UTC)
[edit] Wrong output??
Isn't the output of the mixer a) a signal equal to the sum of the input frequencies (usually filterd) b) the difference of the frequencies (usually the IF) and c)TWICE the original input frequency? See for example heterodyne detection.
[edit] Remove 'tone' tag from article
I'm removing the {{tone}} template from the top of this article. It has been there for some time with no explanation, and with no discussion here. I assume it was added because someone saw the word we in the text. Looking at WP:Manual of Style#Avoid first-person pronouns and one, mathematical discussions such as where we may be found here are clearly made an exception to the normal rule: "It is also acceptable to use “we” in mathematical derivations; for example: “To normalize the wavefunction, we need to find the value of the arbitrary constant A.”" --Nigelj 00:30, 11 November 2006 (UTC)
- Well, I see the {{tone}} template has been re-added, but still no discusssion or comment regarding my quote above from the Manual of Style. I think the problem is either lack of familiarity with mathematical texts, or the same with the Manual of Style. I can't be bothered to keep trying to help here without constructive discussion. --Nigelj 18:57, 11 November 2006 (UTC)
- I don't think the "we" has anything to do with it directly; I get the feeling it was re-added because of the conversational nature of the prose, as a dialog with questions and suggestions rather than as a simple narrative. I've rewritten the entire article to say the same thing more clinically, and removed the {{tone}}; I hope it will be easier to improve it further now (perhaps with NeilUK's suggestions at the top of this page). --Tardis 22:57, 5 December 2006 (UTC)
[edit] Regarding meger with Electronic mixer
- Agree As they are on the same subject, but taking two different approaches: one based on the principles, the other based on the implementation and uses. IMHO the should be merged - Figarema 22:10, 29 August 2007 (UTC)
- Disagree As I explain in the talk page of that article, it needs a very serious edit, but definitely not merging into this. --Nigelj 19:24, 1 September 2007 (UTC)
- Disagree Although the two functions are represented by similar mathematics, a frequency mixer is not the same as an electronic mixer. The articles should be linked and one or the other article should explain the differences. An electronic mixer typically responds symmetrically to the two input ports, while a well-designed frequency mixer has very different response at its local oscillator port than at a signal port. Also, the uses and performance criteria for frequency mixers are very different than for electronic signal mixers. Muennemann (talk) 23:56, 20 February 2008 (UTC)
