Maker Pro
Maker Pro

Ethernet over video cable?

G

GrahamH

Jan 1, 1970
0
Any thoughts on using 75 Ohm video co-ax for 10 or 100 Mbit (strongly
preferred) Ethernet network?
10Base2 provides 10 Mbit over 50 Ohm cable
10Broad36 is supposed to work over 75 Ohm cable but I can find no products
that support it. Is it a dead technology?

I only want point to point connections rather than 10Base2 bus method. An
alternative to Cat5 because the Co-ax already exists. Twisted pair to co-ax
baluns exist but they require one co-ax per pair.

Any suggestions?

Graham
 
I

Ian Stirling

Jan 1, 1970
0
GrahamH said:
Any thoughts on using 75 Ohm video co-ax for 10 or 100 Mbit (strongly
preferred) Ethernet network?
10Base2 provides 10 Mbit over 50 Ohm cable

What happens if you connect a 25 ohm resistor in series with a 10base2
card?
Will 10base2 work at all in this case?
 
J

Joel Kolstad

Jan 1, 1970
0
GrahamH said:
I only want point to point connections rather than 10Base2 bus method. An
alternative to Cat5 because the Co-ax already exists. Twisted pair to
co-ax baluns exist but they require one co-ax per pair.

....hence you'll just need two coax cables per 100Mbps connection. Still
seems like quite an improvement over one coax for 10Mbps, no?

---Joel Kolstad
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that GrahamH <[email protected]>
wrote (in said:
Any thoughts on using 75 Ohm video co-ax for 10 or 100 Mbit (strongly
preferred) Ethernet network?

If your cable runs are reasonably short, the 75 ohm cable will probably
work. Try it.
 
M

Mac

Jan 1, 1970
0
Any thoughts on using 75 Ohm video co-ax for 10 or 100 Mbit (strongly
preferred) Ethernet network?
10Base2 provides 10 Mbit over 50 Ohm cable
10Broad36 is supposed to work over 75 Ohm cable but I can find no products
that support it. Is it a dead technology?

I've never heard of it, but that doesn't necessarily mean anything.
I only want point to point connections rather than 10Base2 bus method. An
alternative to Cat5 because the Co-ax already exists. Twisted pair to co-ax
baluns exist but they require one co-ax per pair.

Well of course. How else would you expect them to work?
Any suggestions?

Graham

In 100 Mbit ethernet over cat5 cable, there actually is a dedicated
transmit and receive. So you can't very well replace both with a single
piece of coax. I think you are going to need to run two pieces of coax.
This coupled with the balun you mentioned should do the trick. The other
two pairs are not used in 100 Mbit ethernet.

If this means you will have to run new coax, then you might as well just
run cat 5 (or better) instead. Make sure you use cable and a pinout that
is compatible with gigabit ethernet, which uses all four pairs of wires.

Mac
 
G

GrahamH

Jan 1, 1970
0
GrahamH said:
Any thoughts on using 75 Ohm video co-ax for 10 or 100 Mbit (strongly
preferred) Ethernet network?
10Base2 provides 10 Mbit over 50 Ohm cable
10Broad36 is supposed to work over 75 Ohm cable but I can find no products
that support it. Is it a dead technology?

I only want point to point connections rather than 10Base2 bus method. An
alternative to Cat5 because the Co-ax already exists. Twisted pair to co-ax
baluns exist but they require one co-ax per pair.

Any suggestions?

Graham

Thanks for the comments so far, generally in-line with my statements of the
obvious. Perhaps I should reiterate that the co-ax is already installed and,
because of its location, is **very** expensive to replace.

So I am hoping for a solution that will provide best speed point to point
tcp/ip (not necessarily Ethernet but that seems the obvious choice).
10Base2/5 achieves this using collision detection and half-duplex. This may
suggest a solution. If I can configure a 10/100BaseT interface to operate
half-duplex and use a balun device to merge rx & tx onto a single co-ax it
might appear to the interface that it effectively had a 10Base2 co-ax
connection. Far fetched or possible?

I would require 100's of transceivers so custom hardware is OK.

Graham


Graham
 
T

Tim Shoppa

Jan 1, 1970
0
GrahamH said:
Any thoughts on using 75 Ohm video co-ax for 10 or 100 Mbit (strongly
preferred) Ethernet network?
10Base2 provides 10 Mbit over 50 Ohm cable
10Broad36 is supposed to work over 75 Ohm cable but I can find no products
that support it. Is it a dead technology?

I only want point to point connections rather than 10Base2 bus method. An
alternative to Cat5 because the Co-ax already exists. Twisted pair to co-ax
baluns exist but they require one co-ax per pair.

Short distances of 75-ohm cable will work on 10Base2, but not over
a few dozen feet. I don't think there's any reasonable hope of getting
100 Mbits.

10Base2 uses DC levels for collision detection, so you need to use
50 ohm terminators, and above a few dozen feet the reflections from
the 50/75 mismatch does you in.

50-to-75-ohm baluns won't work with 10Base2 because they don't
preserve the DC levels.

It's vaguely possible that pull-up networks instead of terminators will
get you the 10Base2 DC voltages with 75 ohm terminations. Hardly
seems worth the effort, but then again I don't know the limitations
on running new cable in your plant. You gotta be pretty desperate
to get to the question you're asking, and I don't want to push you over
the edge :)

Tim.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Tim Shoppa <shoppa@trailing-
10Base2 uses DC levels for collision detection, so you need to use
50 ohm terminators, and above a few dozen feet the reflections from
the 50/75 mismatch does you in.

Use 75 ohm terminators! The fact that terminators are needed shows that
the device input impedances are high, so the terminators have to match
only the cable impedance.
 
M

Mac

Jan 1, 1970
0
Thanks for the comments so far, generally in-line with my statements of
the obvious. Perhaps I should reiterate that the co-ax is already
installed and, because of its location, is **very** expensive to
replace.

So I am hoping for a solution that will provide best speed point to
point tcp/ip (not necessarily Ethernet but that seems the obvious
choice). 10Base2/5 achieves this using collision detection and
half-duplex. This may suggest a solution. If I can configure a
10/100BaseT interface to operate half-duplex and use a balun device to
merge rx & tx onto a single co-ax it might appear to the interface that
it effectively had a 10Base2 co-ax connection. Far fetched or possible?

Sounds pretty far-fetched, but I don't know that much about the signalling
scheme of 10base2.

However, I think John Woodgate's idea will work just fine: Terminate the
line in 75 Ohms instead of 50, and use stock 10Base2. You can literally
put a 75 Ohm resistor across the end of the cable. Don't use any balun or
transformer. As a terminology note, 100baseT2 has nothing to do with
10Base2. The former uses two twisted-pairs, and can span 200 Meters (hence
the 2) while the later uses a single piece of coax. The only similarity is
the 2, which designates 200 Meters in both cases.

I would require 100's of transceivers so custom hardware is OK.

It is not physically impossible to send data over a single cable in both
directions at the same time. It's just that you need to somehow subtract
the local TX contribution to get the RX part. And you have to make sure
the TX contribution doesn't get fouled up by the RX contribution. The
problem is that this all has to work with, in the case of 100BaseT, pretty
fast rise times. I think the rise time is one or two hundred picoseconds
or something. Oh, and you need to maintain 75-Ohm termination at both ends.

Still, you might be able to design a multiplexter that had a 100baseT to
coax conversion system. I'm just not sure it can be done with passive
components only.

I can almost envision how to do this with op-amps, but I don't know if it
would work in practice. If you want me to draw the circuit, let me know.


And now for the most far-fetched idea: Get wireless cards that can be
connected to external antennas. But don't use an antenna, just connect the
two cards to opposite ends of the cable. Please don't get mad at me if it
doesn't work, or if it ruins the cards. And do use a 50-Ohm to 75-Ohm
transformer if you can. Make sure it is rated for the frequency you are
using.

This actually might work, but if it doesn't, it will be because the signal
is too strong or too weak. If it is too weak, you can add an RF amp at the
feedpoint.

If it is too strong, you can put attenuators in line. It might be a good
idea to start with some attenuators in place and then gradually remove
them if you don't get a strong link.

Good luck!

Mac
 
M

Mac

Jan 1, 1970
0
Short distances of 75-ohm cable will work on 10Base2, but not over
a few dozen feet.

I would have agreed with you if I hadn't read John Woodgate's reply about
using 75-Ohm terminators.
I don't think there's any reasonable hope of getting
100 Mbits.

Right, since it is a 10 Mbit protocol...
10Base2 uses DC levels for collision detection, so you need to use
50 ohm terminators, and above a few dozen feet the reflections from
the 50/75 mismatch does you in.

50-to-75-ohm baluns won't work with 10Base2 because they don't
preserve the DC levels.

It's vaguely possible that pull-up networks instead of terminators will
get you the 10Base2 DC voltages with 75 ohm terminations. Hardly
seems worth the effort, but then again I don't know the limitations
on running new cable in your plant. You gotta be pretty desperate
to get to the question you're asking, and I don't want to push you over
the edge :)

LOL

Tim.

Mac
 
T

Tim Shoppa

Jan 1, 1970
0
Mac said:
However, I think John Woodgate's idea will work just fine: Terminate the
line in 75 Ohms instead of 50, and use stock 10Base2. You can literally
put a 75 Ohm resistor across the end of the cable.

No, won't work. 10BaseT transmitters inject current; receivers sense
voltage. With 50% more resistance than you're supposed to have, the
receivers will see 50% more voltage than they were designed for. Since
collision detection is based on seeing more voltage than a single
transmitter's current would imply, you end up with a collision whenever
you try to talk.

I know from experience that 75 ohm cable with 50 ohm terminators works
if the cabling is short. But 75 ohm terminators is definitely a no-no.

Tim.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Tim Shoppa <shoppa@trailing-
edge.com> wrote (in said:
No, won't work. 10BaseT transmitters inject current; receivers sense
voltage. With 50% more resistance than you're supposed to have, the
receivers will see 50% more voltage than they were designed for. Since
collision detection is based on seeing more voltage than a single
transmitter's current would imply, you end up with a collision whenever
you try to talk.

You mean that this digital communications system uses an *analogue*
method of collision detection?

HERESY!

ANATHEMA!

Prepare the racks and the bonfires immediately! (;-)
I know from experience that 75 ohm cable with 50 ohm terminators works
if the cabling is short.
Accepted.

But 75 ohm terminators is definitely a no-no.
Do you know THAT from experience?
 
M

Mac

Jan 1, 1970
0
No, won't work. 10BaseT transmitters inject current; receivers sense
voltage.

Who is talking about 10BaseT? I was talking about 10Base2. For all I know
your objection is correct in both cases, but I'd like to see you say so
explicitly. Anyway, your argument sounds convincing. Maybe one of my other
ideas will work.
With 50% more resistance than you're supposed to have, the
receivers will see 50% more voltage than they were designed for. Since
collision detection is based on seeing more voltage than a single
transmitter's current would imply, you end up with a collision whenever
you try to talk.

I know from experience that 75 ohm cable with 50 ohm terminators works
if the cabling is short. But 75 ohm terminators is definitely a no-no.

Tim.


regards,
Mac
 
T

Tim Shoppa

Jan 1, 1970
0
John Woodgate said:
You mean that this digital communications system uses an *analogue*
method of collision detection?

I will be the first to point out that every digital component is made with
analog parts!
HERESY!

ANATHEMA!

Prepare the racks and the bonfires immediately! (;-)

It's trinary, but still digital :).
Do you know THAT from experience?

Yep. Every mistake possible to make with Thinnet, I made it or saw
it made. Plugging the cable into a video out jack was extremely common!
I won't mention the illegal SHV to BNC adapters and the resulting
fireworks! I still deal with Thinnet and Thicknet on a daily basis, but
most of the disasters were over a decade ago.

Actually, the more I think about the way that 10BaseT transceivers work
internally, it may not be unreasonable to get a bunch (heck, six years ago
they were a buck each on Ebay, the hard part will be finding any at all
today!) of the older lesser-integrated models, modify the resistor
networks appropriately, and use them at 75 ohms. Then you're left with
the problem of finding NIC's with AUI connectors so you can plug them
in.

ARCnet, if I'm not mistaken, used 75 ohm cable. A decade ago, ARCnet
NIC's were being dumped on the surplus market in massive quantities,
but I doubt there's any left today. That ignores the issue of software
support for ARCnet drivers.

Tim.
 
A

Allan Herriman

Jan 1, 1970
0
ARCnet, if I'm not mistaken, used 75 ohm cable. A decade ago, ARCnet
NIC's were being dumped on the surplus market in massive quantities,
but I doubt there's any left today. That ignores the issue of software
support for ARCnet drivers.

ARCnet uses/used 93ohm cable. I can remember very thin centre
conductors and hard-to-get BNC connectors.

Regards,
Allan.
 
M

Michael A. Terrell

Jan 1, 1970
0
Allan said:
ARCnet uses/used 93ohm cable. I can remember very thin centre
conductors and hard-to-get BNC connectors.

Regards,
Allan.

RG-62, the same as used on old car radio antennas.
--
We now return you to our normally scheduled programming.

Take a look at this little cutie! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida
 
O

Octa Ex

Jan 1, 1970
0
I would require 100's of transceivers so custom hardware is OK.

Graham
The 100's of transceivers and connection points is potentially a
problem.
The could be far too many collisions with a large number of
connections to the ehternet..
It would be better if youc could break that down into several
different collision domains.

X X
X
X X
 
Top