Talk:Biphase mark code

SVG picture
I made the picture with Dia, so I could export it in SVG as well. I did it, but I got a wrong output, as you can see in Image:Bmc.svg: I don't know whether it is a problem of the programme or of wikipedia's engine. Anyway I used the PNG version you see in the article. Alessio Damato 14:29, 21 September 2005 (UTC)

Merge with Differential Manchester
If a merge is to happen between these two codes, it might be an idea to merge with Manchester as well. The basic idea of all three schemes is very similar and comparison and contrast may be useful. I like having separate pages for things like this though as a useful reference. A big page isn't that. I vote no on the merge, especially if only BMC and Differential Manchester are to be merged.--Ktims 05:33, 15 March 2006 (UTC)


 * I think it would be better to keep them separated; we might create another page where we compare them, but having one page each is clearer. Alessio Damato 08:54, 1 June 2006 (UTC)


 * I agree with Alessio. I vote no, too, for the same reasons. It also allows for technical detail that might be out of context in a merged topic. Aki Korhonen 18:28, 18 July 2006 (UTC)


 * If there were some difference between differential Manchester and biphase mark code, I would agree with you.
 * However, as far as I can tell "differential Manchester" and "biphase mark code" are synonyms for exactly the same thing, so I strongly feel their articles should be merged.
 * If you feel that there is some difference between them, please give an example signal where a biphase mark code receiver would decode a different bit sequence than a differential Manchester receiver. --75.41.34.231 14:38, 22 May 2007 (UTC)


 * yes you are right: they are based on two sightly different approaches but they produce exactly the same output, even if it is shifted of one clock period... The two encodings have different names, so I would keep the two articles separated, stressing the fact that they create the same output with an example. I'll work on it as soon as I have some time. Alessio Damato 13:17, 24 May 2007 (UTC)


 * I don't understand. Two 2 articles for the 2 different names given to the same thing? Why not merge them? Would you give "München" and "Munich" two completely seperate articles? --76.209.28.72 19:33, 5 June 2007 (UTC)


 * If there are two names for exactly the same thing, it should get one page, and not two. The fact that the output is shifted by one-clock period is not a real difference, as the clock given on the drawings is just for demonstrative purposes and has nothing to do with the coding itself. 85.179.4.247 (talk) 12:12, 6 December 2007 (UTC)

Page title
Can we really consider this to be a proper noun? I think the page should be named 'Biphase mark code' instead. This would match the other line codes here, as well as Wiki policy.--Ktims 07:09, 1 June 2006 (UTC)


 * I agree Alessio Damato 08:54, 1 June 2006 (UTC)

Sources?
Bot wants sources. All I have is Stallings, which doesn't mention BMC, only Manchester and DManchester. Anyone got some reputable material we can reference?
 * Not sure if these help: google scholar search result (KH MOREY 1962, RC HANSEN 1962, etc.)
 * Ezekiel Bhasker 21:18, 11 July 2007 (UTC)

Clock Frequency?
The article states that "the frequency of the clock is twice the bitrate of the original signal." From the diagram, it seems to me that the clock frequency is equal to the bitrate of the data (original signal). 63.167.168.8 20:58, 5 March 2007 (UTC)
 * Yup, I'll correct it. Either would work fine in practice (symbol clock detects either edge, bit clock detects rising edge, for example), but the article and diagram should obviously match. --Ktims 04:27, 7 March 2007 (UTC)
 * Still not sure about this one, "the symbol rate must be twice the bitrate of the original signal", only 1 bit of data is transmitted per symbol, so the symbol rate is the same as the bitrate, should perhaps be changed to "The data is encoded onto a clock with twice the frequency of the bitrate" or similar. If this is incorrect please delete.--80.44.157.77 15:16, 27 April 2007 (UTC)

We're using one technical definition of the term "symbol rate", which is "how often the voltage on the line can change" (symbol (data)). Since in biphase mark code, the voltage can change twice per bit, that's 2 "symbols" per bit. Since the symbol rate of "biphase mark code" is double the symbol rate of non-return-to-zero, the bandwidth required for "biphase mark code" is double the bandwidth required for non-return-to-zero (at the same bitrate). In 8B/10B encoding, a group of line voltage changes (symbols) (in this case 10) decodes into 8 bits. Alas, some people look at the entire group (10 symbols) and call it one "symbol". I wouldn't be surprised if this were another perfectly valid, official definition of the word "symbol", but it sure makes things confusing. What can we do to make this article correct, without being unnecessarily confusing? --75.37.225.73 03:49, 10 May 2007 (UTC)

Would this be less confusing (and just as correct)? Do things the same as Return-to-zero: use "bandwidth" instead of "symbol rate", replacing the confusing sentence
 * "When encoding, the symbol rate must be twice the bitrate of the original signal."

with
 * "The bandwidth required for biphase mark code is double the bandwidth required for non-return-to-zero, at the same data rate."

? --75.41.34.231 03:28, 18 May 2007 (UTC)

DC characteristic
Finally, BMC coded signals have zero average DC voltage, This is not correct. Average DC value of 1 is zero, but each 0 gives DC shift compensated only by next 0. Thus zero DC voltage can be achieved only in series with even number of 0. In the series of multiple 1 with a single 0 there is a non-compensated DC voltage. The FM0 encoding have the same frequency characteristic (it differs from BMC by opposite rule of encoding - transitions between bits and additional transitions in the middle of 0). Both of them have bandwidth from 0 to F. Manchester Encoding and Differential Manchester Encoding are free of this problem - they have bandwidth from F/2 to F.

FM0, Biphase mark, Manchester and Differential Manchester can be grouped together. They are all self-synchronized two-level encodings. They differs by rules of placement tranisition between two levels:

FM0 have transition between each bits and transition in the middle of the 0. Biphase mark have transition between each bits and transition in the middle of the 1. Manchester have transition in the middle of each bit and transition between same bits. Differential Manchester have transition in the middle of each bit and transition before 0. 195.140.182.162 08:50, 2 November 2007 (UTC)Vitaly Nasennik

BMC coded signals have a zero average DC voltage. For every "1" data bit, the average of the second half of the data bit and the first half of the next data bit has an average DC value of exactly 0. For every "0" data bit, the average of the second half of the data bit and the first half of the next data bit has an average DC value of exactly 0. So the average DC voltage for BMC is exactly 0, when measured from the center of any bit to the center of any other bit. --68.0.124.33 (talk) 20:42, 2 April 2008 (UTC)

You've lost first half of the first bit and the second half of last bit. —Preceding unsigned comment added by 89.189.191.4 (talk) 08:25, 13 September 2008 (UTC)