Universal Laborator System!

[Shahriar]

Hi

Imagine 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

[Staigen]

Hi Shahriar

Isn'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

[audioguru]

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)

[Staigen]

Hehe, something for you Shahriar! Cheap, simple and dirty! Only a few Cmos gates! ;D ;D ;D ;D
Hehehe


//Staigen

[Shahriar]

;D ;D

Yeah, I am Going to build it.  ;D

Although I didn't understand anything, but I thank Audioguru, it is very good for a start!

Shahriar

[Shahriar]

Dear Staigen

As I Know, they send digital Data!

For modulating Sound, I think 100Khz for carrier frequency is a little low, Isn't it?

Shahriar

[Staigen]

Hi Shahriar

As 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