Indiglo Posted March 25, 2004 Report Share Posted March 25, 2004 Hi guys I am new here, nevertheless here it is.My current project is to design and build a multichannel optical fiber link. The questions I got are related to the speed of the link. In order to achieve high transmission speeds(high BW/data rate), would this depend exclusively on the transmitter? If so, and suppose you are feeding the Tx with analog audio (not more than 20kHz)what is the amplifier in the transmitter for if you can have it at the receiver as well? And finally, should there be some matching between the transmitter and the reveiver apart from the transmisiion frequencies?Thanks in advance Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 25, 2004 Report Share Posted March 25, 2004 The speed of the transmission is almost instantaneous. This means the data will be sent at the rate of 20k hertz or as fast as the data is present. You could also clock the data at a very high rate and get every last piece of the signal. This means you will have data that is extremely accurate. So clock the slow time base data of 20k hertz at 1Mhz and get a lot of data from it. Quote Link to comment Share on other sites More sharing options...
Indiglo Posted March 25, 2004 Author Report Share Posted March 25, 2004 are you sure that someone can actually do this Kevin? I am not sure I understand ??? you actually mean "clocking " it in terms of sampling it? Then I have to use A-D converter and D-A respectivelly, plus I have to change the modulation scheme if I wanna go foe digital (PCM, etc). Initially I am after a purely analog link if you know what I mean. ;)The question is if there is a way to transmitt at a higher speed an audio signal than the frequency that the signal by nature propagates... Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 25, 2004 Report Share Posted March 25, 2004 I was refering to only digital. I was talking about sampling, but it does not require an AD. The data rate would still be 20k hertz too. This is just a way of using the high speed transmission. With modulation, though, instead of 5 minutes to transfer the data it only takes 30 seconds. Quote Link to comment Share on other sites More sharing options...
MP Posted March 26, 2004 Report Share Posted March 26, 2004 Indiglo, your circuit will simply change the electrical data to light and then back to electrical data again. The reason to do this is normally to send data through long signal lines without electrical interference.You should not have to worry about sync problems with an analog signal. The only bandwidth problems you might encounter are those of the amplifier that converts the signal to light and the one which converts the signal back again. If you start clipping the signal, then the conversion will sound awful. One area of concern is signal loss. At audio frequencies you will see a 0.25 decibal loss per km for good cable. Lower standard cable can be as high as 3 to 4 db per km. The phone company gets around this with repeaters. Some research on telephone fiber optic practices will help you, I think.As Kevin was pointing out, you can digitize your signal to give it more strength and speed of transmission.MP Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 26, 2004 Report Share Posted March 26, 2004 It is a very interesting experiment to send analog data down a fiber optic cable. The luck you would have could rival that of a cable. The only problem with cable is that you are limited to about 1 gigahertz. I think you might try to modulate demodulate the signal using the LED and the photodiode before inserting the fiber optic. Quote Link to comment Share on other sites More sharing options...
Indiglo Posted March 26, 2004 Author Report Share Posted March 26, 2004 thanks for the feedback all,well, analogue transmission is just a small tiny step to what I wanna do. In fact I don't know what I am gonna do later on, but I agreed at fisrt as an introduction to do a link of a single channel mono-directional from an audio playback source - to the modulation, throught the fiber, demodulation amplification at the receiver and right out from a set of speakers. So, it must be a real-time application 'cause it involves playback and not storage. And sound is just the beginning as I said, cause then the 2nd channel will involve video transmission (eehhmm..somebody said something about bandwidth ;D)...so it is not gonna be an easy task. Hopefully I came across some audio and video /VHF amplifiers to do the trick.Though I am working on it, anybody who reads this might as well drop a few lines for some additional guidance..thanks again!PS: MP, though I understand that this is a handy use of fibers, it could not be only for telecomms but also for many many sources of data through the same fibre. If you have heard of WDM, then you know that one can achieve bandwidth in the order of THZ. (In the lab I am using a 1m fiber reel , so distance attenuation isn't a problem) Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 26, 2004 Report Share Posted March 26, 2004 You don't even need modulation if you don't want to utilize the short time base. The question is, where do you want to save time. In modulation, what you are doing is compressing 5 minutes worth of data into 30 seconds. 30 seconds is the transmission time. In order to that, you have to already have the 5 minutes of data generated. So you have to store it digitally for modulation. This can be useful when you have only 5 minutes. If you are continueing to generate the data, then modulation won't do any good. Make it a high speed system with data that is already generated. Quote Link to comment Share on other sites More sharing options...
Indiglo Posted March 27, 2004 Author Report Share Posted March 27, 2004 Exactly, that's what i am saying. I am trying to see if in real-time transmissions a fiber link will do any better than the standard coax or twisted pair. Also, I ma just wondering if the time for the audio to reach the speakers will be less than the propagation time within the CD player or any other audio playback device. I suspect it will, but it willl be a difference in the order of nsec. ;D Let's see... Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 27, 2004 Report Share Posted March 27, 2004 I have a question. I have read, I believe, that wave propagation down a transmission line results in a train of waves. Is this true? It would make sense that a bit originating from a long distance and appearing at the other end would not happen. Instead you have a train of waves on the line at the same time. Quote Link to comment Share on other sites More sharing options...
Indiglo Posted March 27, 2004 Author Report Share Posted March 27, 2004 I think that would be ideal, don't you think? ;)If that was the case, then I wouldn't break my head trying to find what to do. Perhaps you refer to ISI (intersymbol interference) which mainly has to do with digital pulse-train that after some length the pulses from 2 different signals will overlap eachother and at the receiver it would be very hard to distinguish what is what...I think that this has to do with transmitting via a coax and not a fibre. But still I am a long way from digital transmission. I still have to find out what to do with the analog link and then I'll see. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 27, 2004 Report Share Posted March 27, 2004 A train of waves is different from the problems associated with a coaxial cable. Standing waves aren't a problem. This is the reflection that is talked about. I think the standing wave can only cause a problem when the changing signal produces different standing waves, thus affecting the input and output bias. Only if you are serious would you find that the standing wave causes a problem. Quote Link to comment Share on other sites More sharing options...
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