Shahriar Posted February 5, 2006 Report Share Posted February 5, 2006 HiImagine you want to build a Laboatory System which has a common Shield cable through all Sets.The system should have the capability of talking persons to each other seperately. I mean in the following System with 4 Sets, Person No.1 wants to talk to No.3 and No.4 Wants to talk to No.2 without Interfering their sounds. how is this possible?My plan is Mic Amplifier No.1 & No.3 should Modulate their signal in a seperate Frequency (i.e. 1Mhz) and the same for No.2 & No.4 (i.e. 1.1Mhz)ThanX Shahriar Quote Link to comment Share on other sites More sharing options...
Staigen Posted February 5, 2006 Report Share Posted February 5, 2006 Hi ShahriarIsn't this similar to the intercom system that used mains as transmission line?They usally used 100 Khz, 120 Khz and 140 Khz as comunication frequency.I reparied one such intercom once.//Staigen Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 5, 2006 Report Share Posted February 5, 2006 I worked with large intercom systems (hundreds of loudspeaking stations) for many years.The best ones used PAM which is Time-division Amplitude Multiplexing.Internally inside the exchange, a single wire carried the voices or background music of 20 sources. The wire was multiplexed at a very high frequency that had 20 "time-slots". The time-slots were spaced a little to prevent crosstalk and each carried a source that was "chopped" in time with a sample-and-hold circuit using Cmos transmission gates.At the receiving end, transmission gates demodulated then filtered their time-slot.The sound quality was fabulous and I slightly modified one to meet the "hi-fi" standards for the 1st one for paging at many airports.The stations used voice-switching to avoid long-distance acoustical feedback howling then later systems used DSP acoustical echo cancellation.Ordinary audio was carried in a 4-wire cable to each station. I think that carrying the high frequency multiplexed signal all over the place would be too complicated. 8) Quote Link to comment Share on other sites More sharing options...
Staigen Posted February 5, 2006 Report Share Posted February 5, 2006 Hehe, something for you Shahriar! Cheap, simple and dirty! Only a few Cmos gates! ;D ;D ;D ;DHehehe//Staigen Quote Link to comment Share on other sites More sharing options...
Shahriar Posted February 5, 2006 Author Report Share Posted February 5, 2006 ;D ;DYeah, I am Going to build it. ;DAlthough I didn't understand anything, but I thank Audioguru, it is very good for a start!Shahriar Quote Link to comment Share on other sites More sharing options...
Shahriar Posted February 5, 2006 Author Report Share Posted February 5, 2006 Dear StaigenAs I Know, they send digital Data!For modulating Sound, I think 100Khz for carrier frequency is a little low, Isn't it?Shahriar Quote Link to comment Share on other sites More sharing options...
Staigen Posted February 5, 2006 Report Share Posted February 5, 2006 Hi ShahriarAs I Know, they send digital Data!If you mean the intercoms i talked about, there isn't anything digital there, they come in the 1960:ies or so, and used AM in the beginning, and later FM, because of much noice and interference. And they used freqs around 100-200 Khz! They where fully analog!For modulating Sound, I think 100Khz for carrier frequency is a little low, Isn't it?No, even 100 Khz works just fine, it was not hifi! For hifi you maybee must go up to at least 400-500 Khz.//Staigen Quote Link to comment Share on other sites More sharing options...
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