X-mission of audio over 2.5kms distance

[Samuel Jayaraj]

I have this big challenge before me. A potential client has already installed multi-core telephone cable over a distance of 2.5kms between two of their buildings. The space between has many roads and other structures. They want audio (particularly speech like in a paging system as well as music) to be transmitted from one building to another over this distance of 2.5kms using either one pair or two pairs of telephone twisted copper. The cable has foil but no other shielding.

What means can I use to undertake this challenge? Will 100v or 70v line transformers do or should I take another route? Signal degradation needs to be at a minimum. They are not prepared to incur the cost of digging up and laying another dedicated cable.

Thanks for any inputs.

[moamps]

What signal types are in rest of pairs?

[markp]

Convert to digital and back to analog. There are boxes out there for just this purpose.

[Geek]

That sounds the best solution.

The only other thing I can think of is a carrier current system. Use one twisted pair as a balanced line and your radiation will be minimal. It'll be as good as the care you put into the CMRR at the RX end.

[Enzo]

Are yu required to use the cable, or are they just offering a couple unused pairs in it for you? If all they want is the signal getting back and forth, consider other means too besides the cable. Is it both directions of just one way?

That is not all that far, so is there a reason radio systems could not be used? I would think that FM would be reliable and have all the bandwidth you might ask of it. And I think you could find off the shelf stuff to do it. You might even contact companies like Clear Com and other communications equipment makers.

[Samuel Jayaraj]

moamps,

The rest of the cable pairs would be carrying normal telephone signals.


markp,

I will investigate this possibility. Thanks, and are there specific brands that do this job well?


Geek,

I was also thinking of a balanced line but the fact that there is no shield bothers me. How about using a low power Aleph X amp for transmission; then at the other end bring down the voltage level through resistors and use the best CMRR method possible to retrieve the signal.


Enzo,

The cables are not just being offered. It is mandatory to use these. It's got to do with government sanctions etc., Hence, FM is also ruled out.

[Geek]

Originally posted by Samuel Jayaraj
Geek,

I was also thinking of a balanced line but the fact that there is no shield bothers me. How about using a low power Aleph X amp for transmission; then at the other end bring down the voltage level through resistors and use the best CMRR method possible to retrieve the signal.

Twisted pair cables in multi-lines are fairly balanced and don't need a shield. Your Aleph, if it drives the pair in full differential mode, could work well.

[markp]

Calrad make a CAT-5 based system that will work for you even though you are going further than it is rated. Look at part number 95-1043 in the Calrad catalog. It is audio and video but you dont have to use the video.

[lowlevel]

I have had to do this my self a couple of times but there are a couple of newer options.
Some of the cat 5 devices could be worth a look but I don't know iff they will do the distance.

You do need to keep the signal levels undercontroll or you will have cross talk problems into the other services.
then there are the legal problems but I don't know coms law in your part of the world so lets not bother about that.

What I have had sucess with in the past.
Paging mic from gate house of large factory complex. sender box consisted of psu, 1 watt chipamp board (LM386) driving telephone transformer you want about .6 volt rms max to line.
the LM386 will have enouh gain but if you want better noise immunity on the input side a baisc mic pre will help. dont forget to cap couple the TX and provide a terminating impedance of say 560ohms across the amp side of the tx.
Rx box consists of a telephone transformer terminatimg resistor & a pad to match to your amp input,
I've had them run ok over a km 2 K shouldn't be a problem.

Give it a go its cheap as chips.

I have run 100v line systems too over 2.5K but not in the same sheath as anything else. you will still need to balance the RX of a 100v line type system. ( resistor attenuator into ball TX )
cheers