ADSL.. where to start?? 1

[aabasiry]

Hi All,
I will start by introducing myself, I am a Professional Engineer in the province of Alberta-Canada. Also a partner in a small company (4 of us). We build instrumentaions and sensors for the oil and gas industry.

We have a potential project coming up and I am doing some background research into it to get familiar. One part of the project requires data transmission over a long distance of about ~4 Kms (~13,000 ft) using Unshielded, twisted pair cables (UTP). I thought of using ADSL technology for this but except for the average engineering knowledge that I gathered by reading some online resources, I am totally unfamiliar with it.

The main aim is to build what resembles an ADSL modem at either end of the cable to transmit data back and forth.
I do not want to delve into a whole new world of physics and communication theory (other than what I really need to know) in order to develop such system since time and budget do not really permit.

What I am looking for is an off-the-shelf system (i.e. a chipset or such like) which we can deploy into the system with little glue-logic/interface. If it is based around a DSP or FPGA, then preferably it come with the ADSL application code included (even if we have to buy them from different outfits).

Does such thing exist at all? Do you have experience with any particular product/manufacturer..etc

Cheers,

 

[MikeHalloran]

I wouldn't use DSL (Symmetrical OR Asymmetrical) on a bet for industrial data.

'SL' refers to 'subscriber line', which is the run between the telco's 'central office' and the subscriber's demarcation point. I think it's physically limited to 1300 feet or so. In between the two DSL ends is whatever the telco decides to use and maintain. You of course pay for the installation and the service, etc.

It's a really bad idea if you have data that _must_ get to its destination, and especially if it must get there in a known short time frame.

Given that you appear to have verified that you can run cables (i.e., you own the land or have access to it), the only other thing you haven't answered is how much data you need to transfer in what kind of time.

E.g., I think you can do 9600 baud over 4km with current loop or with so-called 'short haul modems'. If you need a lot more bandwidth than that, you might run optical fiber instead of copper.

How about engaging a local sparky to help you?


Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Mike I believe it is limited to more like 13,000ft.

Why are you rolling your own? Since you don't want to delve that deeply into it why not avoid the learning curve and just buy it.

What kind of data are you shipping and how much?



Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

I was told that the ADSL line length limit is 20,000 feet. My house is 22,500 feet from the CO (naturally). But I've read about newer variations of ADSL that can cover vast distances at lower data rates, or short distances at insane data rates.

I've been in hotels where they use an in-house ADSL system to feed the 'Free Internet' up to the rooms using the existing telephone wiring. Each room has a ADSL WiFi Router screwed to the back of the desk. So obviously, cheap off-the-shelf equipment must be available.

If anyone is worried about reliable delivery of data, then the modem solution (if that actually helps) could ALSO be attached to the same pair of wires for an extra few hundred dollars in equipment costs.

 

[aabasiry]

Thanks all for the replies.
Sorry. I forgot to mention the data rate. The minimum requirement is ~ 150 kbps downstream and less than 10 kbps upstream. But, it is better to design for 200 kbps downstream for future expansion. The data is mostly video images and/or sound waves. It may not look as much, but when transferring it over 4-5 km distance it becomes a bit of challenge, specially the cable used is quite capacitive (~ 200pf/meter or ~60pf/ft)

The fiber optic option is ruled out because the UTP is already in place and we do not have the means/option to change it.

If there's a system out there which we can adapt we would look into buying it. I am not really in favour of making our own from scratch. No need to re-invent the wheel if I don't have to.

 

[VEBill]

"data transmission....~4 Kms"

Another option to keep in mind (perhaps as a back-up plan) would be to simply ignore the existing telephone wiring and instead use any number of inexpensive point-to-point "wireless" (radio) data links. 4km range is well within the capabilities of fairly cheap systems, provided that there is something close to a direct line of sight path.

The telephone wire link would (in theory) be more reliable, at least until it gets knocked over by an accident.

 

[aabasiry]

Thanks VE1BLL..
Wireless is not an option too. Did I mention that the 4 km distance is actually drilled inside the ground

 

[VEBill]

LOL.

That's the old "Oh, and one more thing..." type of requirement.


Example (from legend): "Thank you for attending the Bidders Conference. Oh, and one more thing. These new systems must be installed into the submarine fleet by way of the only available access: a 3-inch diameter pipe, about four feet in length, with a 90-degree elbow about half-way along."

 

[aabasiry]

That's a classic

 

[MikeHalloran]

How many pairs are available in the UTP?



Mike Halloran
Pembroke Pines, FL, USA

 

[aabasiry]

1 pair (two wires)

 

[sreid]

Perhaps of some interest.

http://en.wikipedia.org/wiki/Adsl

I assume that all of these standards specify the kind of wires to be used.

I believe, in theory, that the signaling rate over any transmission line is only limited by noise [thermal] but in practice its outside interference.

The basic scheme is to characerize the ampliture and phase shift with frequency and then pass the data through an equalizing [digital] filter. You may have to consider doing this.

One way to do this is to send pseudo random noise down the line and and FFT the received data to get the frequency and phase shift. Then have an "Arbitrary" digital filter at the sending end to equalize the data prior to transmission.

Having said that, best to be done by a knowledgable consultant [A University Grad Student did mine for an entirely different purpose].

 

[VEBill]

I assume that in practice, the ADSL chipset and reference design would take care of all that channel characterization. The system level designer shouldn't have to 'redesign that wheel'.

If the 4 km is vertical, then he will have plenty of "interesting" packaging issues to deal with.

 

[MikeHalloran]

ONE pair?
You got specs, or a Belden number?
Or did somebody just spin some hookup wire with a drill?

Given 4km without a spare pair, you're screwed even if you _can_ get it to work.

I'd use it to pull fiber. Actually, I'd use it to pull a proper pulling cable, and I'd use that to pull at least three pairs of fiber.






Mike Halloran
Pembroke Pines, FL, USA

 

[sreid]

A Star for Mike!