Point to point coaxial cable communication - Page 1
Forum section: electronics / projects

author: mmuj
author_rank: Newbie
timestamp: April 22, 2016, 04:25:41 pm
content: HiI am working on point to point communication system over dedicated coaxial cable.Required Data rate = 100kbpscable length = 5kmI am looking for suggestion/design ideasIn one of my previous projects I used wire line modem (CMX866) successfully over similar distance but baud rate was 2400.Can I use two DSL modem ICs for such communication? are DSL chipset ICs available for Digikey/Farnell? i couldn't find any from product profile of TI, Analog or ST etc.I know Broadcomm is a key player in this market but they don't have good reputation for supporting small volume/ niche market customers.Any other ideas?Thanksmmuj

author: Marco
author_rank: Super Contributor
timestamp: April 22, 2016, 05:49:32 pm
content: ADSL2 range extended is designed for that kind of distance, but won't the chipset expects 2 pairs?G3-PLC seems the only other suitable big standard.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 22, 2016, 07:05:38 pm
content: Number one question is why specifically COAX? Can you use fiber or microwave instead? Coax has horrible losses. Long distance voice/data over coax was phased out in the 1980s for a reason. Ie L5 Carrier or 10Base5 type systems..Can you have repeaters every 1 to 2 Km?What you want is called a "Short Haul Modem" Or " Ethernet Extender" if this is a one time use and you have to use Coax. Something like AT-MC606 from Alliedtelesis or similar... Good for a Kilometer or Two maximum.The phone company calls the twisted pair version T1, E1, ADSL etc...The cable TV standard is called DOCSIS, and is very expensive to implement..Or are you seriously designing a product to do this over a cable TV network? SteveSteve

author: Marco
author_rank: Super Contributor
timestamp: April 22, 2016, 07:40:38 pm
content: Quote from: LaserSteve on April 22, 2016, 07:05:38 pmTrying to use anything above a couple 100 kHz doesn't make a lot of sense, it's unlikely it will be able to adapt to this kind of cable.

author: mmuj
author_rank: Newbie
timestamp: April 25, 2016, 10:12:42 am
content: Thanks for everyone contributionCommunication needs to work over an existing infrastructure which has coaxial like cable.I also thought about PLC (G3 or something similar).Now to through spanner in the work. Operating temperature requirement is at least 150C.AFE031(PLC AFE chip) has automatic thermal shut down set to 150C so it is not going to work.

author: dr.diesel
author_rank: Super Contributor
timestamp: April 25, 2016, 11:01:50 am
content: What kind/type of coax is it?

author: Marco
author_rank: Super Contributor
timestamp: April 25, 2016, 05:23:01 pm
content: Quote from: mmuj on April 25, 2016, 10:12:42 amYou are combining so many niche requirements at this point that to expect something COTS is optimistic.I'd look to either develop your own OFDM modem software (if you have more time than money) or license some of the available solutions (vice versa) which are out there, that way you have a much wider selection of hardware available. The computational requirements aren't very high.

author: Zero999
author_rank: Super Contributor
timestamp: April 25, 2016, 09:06:47 pm
content: Why does it have to be co-axial cable?Standard PTFE wire can work at over 150°C and is available as a screened twisted pair.http://www.gore.com/en_xx/products/cables/highdatarate/aircraft/shielded-twisted-pair-wire-2.html

author: dr.diesel
author_rank: Super Contributor
timestamp: April 25, 2016, 09:32:15 pm
content: Quote from: Hero999 on April 25, 2016, 09:06:47 pmApparently it's already in place and he's being forced to reuse it.

author: max_torque
author_rank: Super Contributor
timestamp: April 25, 2016, 09:40:44 pm
content: 5km at 150degC ?? where is this, Mars??(or down a very deep mine / borehole i guess?)

author: dr.diesel
author_rank: Super Contributor
timestamp: April 25, 2016, 09:57:05 pm
content: I can't think of any industrial building that is 5km long, and wouldn't think a tunnel or shaft would be that hot, unless it's a power cable tray. Which makes it that much worse.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 25, 2016, 11:23:23 pm
content: Borehole Instrument ? Geothermal Steam ? Refinery?Steve

author: SeanB
author_rank: Super Contributor
timestamp: April 27, 2016, 12:48:40 pm
content: I would guess refinery, chemical plant or a large bulk carrier. I think the 150C is not doable, but 120C will be doable with industrial packages, though better will be to get active cooling in the cabinets it will go in, using a Coanda effect cooler if air is available.

author: max_torque
author_rank: Super Contributor
timestamp: April 27, 2016, 06:30:24 pm
content: Quote from: SeanB on April 27, 2016, 12:48:40 pmThat's either a seriously, impressively, amazingly long ship, or the guys putting the cables in were paid by the meter (and hence wired everything, several times round the hull to make the most money).............

author: SeanB
author_rank: Super Contributor
timestamp: April 27, 2016, 07:03:39 pm
content: Port side has a loom running along from stern to bow at deck level, then it returns at bilge level, then wanders around engine room to starboard and does the same, then it goes up through the crew section to the bridge. I can easily imaging 2km of cable just in that one run if you are using a low speed bus.

author: Delta
author_rank: Super Contributor
timestamp: April 27, 2016, 07:34:30 pm
content: I'm guessing this is for wireline tools used in oil & gas drilling, (The drillstring is tripped out of the hole, then tools (various sensors etc) are winched down the well) and the coax is part of the wireline umbilical...With enough brute force and ignorance you should be able to drive 100kHz along 5kM of coax.ORModulate a few-MHz RF signal, with a bit of impedance matching and a sensitive receiver this should do the job.

author: Scrts
author_rank: Frequent Contributor
timestamp: April 27, 2016, 08:09:59 pm
content: Quote from: Delta on April 27, 2016, 07:34:30 pmI would say DOCSIS or DVB-C is the way to go then. Full DVB-C modulator with all the modulation capabilities fits into EP3C16 FPGA. If the design would be stripped to, let's say, QAM16, then it would probably fit into the smallest FPGA.Other than that, maybe Cortex-M4 or -M7 could do QAM modulation, but you need to hook up a DAC too.

author: Marco
author_rank: Super Contributor
timestamp: April 27, 2016, 08:56:37 pm
content: 200+ dB attenuation at 50 MHz ...

author: station240
author_rank: Unknown
timestamp: April 27, 2016, 09:24:17 pm
content: Quote from: mmuj on April 25, 2016, 10:12:42 amUse a Peltier Device to cool the electronics, should work in theory.I checked and you can get ones that are rated to 150C.Of course then you still need heatsinking, fans etc for the hot side.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 27, 2016, 09:43:20 pm
content: BFO, Which means before fiber optics, telecoms used coaxial cable for very important long distance trunk lines. SSB carriers were used for each audio channel spaced ~ 4 KHz apart. Very specialized low loss coax was made into bundles, and buried two meters down. . In the US, these cables were retained to the late 1980s, early 1990s for secure communications that could not go over our extensive microwave systems. My late uncle used to maintain a small part of the system.The L cables are abandoned in place near where I live, and two of them cross my favorite hiking path.The attenuation is atrocious, and the frequency response of the cable changes with temperature, so for the "L" carrier coaxial systems, buried, remote controlled, adaptive equalizers were used.https://en.wikipedia.org/wiki/L-carrierNote the repeater spacing as bandwidth increases.Thus the first step is to characterize the cable when hot.Then to determine if you need bi-directional communications.Large amounts of engineering data on how this was done is in the Bell System Technical Journal.Steve

author: Marco
author_rank: Super Contributor
timestamp: April 27, 2016, 09:54:49 pm
content: G3-PLC/PRIME is pretty much exactly what he needs modulation wise, the only problem is the temperature.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 27, 2016, 10:01:55 pm
content: After reading the about the standard, I'd agree.. OFDM would work nicely.Steve

author: mmuj
author_rank: Newbie
timestamp: May 02, 2016, 03:38:33 pm
content: Thanks for everyone's contributionAt the moment best option apparently is PLC G3/PRIME.