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Re: Serial+power over single coax cable
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Ground your rig before it grounds you.

Tauno Voipio (OH2UG, since early 60's)
tauno voipio (at) iki fi


Re: Serial+power over single coax cable

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Thanks for mentioning it, Hans-Bernhard.
It depends on the circumstances whether alternatives exist.
I know of more than one remotely operated submarine used
for inspection, that they use the coax for video, data and
power.

Rene
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Re: Serial+power over single coax cable

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Considering that working up a SPICE model of multiple nodes does not take
that long to do, this would answer such questions quite rapidly. It would
also allow exploring a number of options of ideal supply voltage and
current.

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Re: Serial+power over single coax cable
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To me this is ridiculous.  All you need is ohms law and an old
envelope to scratch out a preliminary feasibility study.  If things
are orders of magnitude out of whack, stop thinking about it.  If
there is are orders of magnitude of margin, go for it.  If it is
close, hire Paul Bennett to resolve it.

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Re: Serial+power over single coax cable

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Some form of Manchester coding is often used, when you want to get rid
of DC-components, which also would permit separating the DC power and
the signal.

As a coaxial cable has a large bandwidth, you could even send it on
some RF carrier (say 30 MHz) and run FSK or even amplitude modulation.
However, if this is done, you have to be careful about the line
termination, the station branch lengths and the minimum distance
between the branches.

Paul
  

Re: Serial+power over single coax cable

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You might be able to make it work
with cable modems.



Re: Serial+power over single coax cable

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Yes, take a DDS that does some FSK or PSK modulation
for you. Coupling onto the cable is done with caps
holding the DC voltage. For the modulation frequency
you need correct AC termination, meaning a 50 Ohm
behind the caps.

Rene
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Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

Re: Serial+power over single coax cable
Hi Dejan,

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Power should not be a big deal with coax but make sure it's all fused
and protected.

As to data I'd modulate it onto a carrier, probably FM if it needs to be
cheap. I'd pick a band where the likelyhood of interference is lowest,
preferably ISM like the 900MHz band. Just in case somebody makes a
mistake, a connector shell comes loose etc. That has the other advantage
that you'll be able to obtain cheap HW. You may then want to go with
whatever modulation scheme the popular chipsets use.

You could probably even go 2.4GHz where HW is really cheap but that is a
challenge for longer cable runs and for the distribution and router
circuitry. Just resist the temptation to leave it all at baseband. That
can cause serious susceptibility. I have seen lots of grief in
non-twisted baseband data cables, such as 'it all works unless somebody
uses the elevator...'.

Regards, Joerg

http://www.analogconsultants.com

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