Serial+power over single coax cable

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I need to transfer ca. 5MB/S over coax cable, that should simultaneously
be used as a power supply line. There would be several stations, LAN-like...
Any suggestions?

- Dejan



Re: Serial+power over single coax cable

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Way easier with CAT5 and ethernet in a star
configuration, essentially off-the-shelf.

How much power?  Do you mean bus topography?


Re: Serial+power over single coax cable

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It would be easier. However , the requirement is coax. At the moment, the
power drain from
the coax is not an issue.

Yes - it's a bus topology. Also, it would be a master-slave system, so
there's no need for
colision detection. Slaves only respond when asked by master, one at a time.

Generally, what modulation types are preferred?

- Dejan



Re: Serial+power over single coax cable
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Over what distance? Is it 5M bytes or 5M bits?



Re: Serial+power over single coax cable
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Just as sidenote : coax can carry much more power.
Especially when I think about RG214 and such,
doing 5kVrms

Rene
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Re: Serial+power over single coax cable
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That would depend greatly on the power needs of each station, the
total length of the line, the distribution of the stations, and the
ohms/unit length of the cable used.

Start by deciding if the cable will distribute the power at all,
then consider multiplexing schemes.

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Re: Serial+power over single coax cable

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The main problems in this will be the node PADs where the power and the
signals will be separated. The consideration here, of course, is avoiding
any form of ground-loop that may disrupt the proper processing of the
network signals. I predict that you will need to sit down with SPICE and
run plenty of simulations on your candidate node PADs. Don't forget to
model the coaxial lengths between systems as well as the nodes.


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Re: Serial+power over single coax cable

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Separating the power from the signal will not be that difficult.
Get the signal through caps and the power through inductivities.
On both ends.
For the bidirectional signal, a rotator separates the waves in
either direction. Their implementation depends on the frequency
range.

Rene
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Re: Serial+power over single coax cable
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No, the first problem is to find out if the system has any chance
of working.  To illustrate, lets assume the cable is RG58U, 100
meters long, with a station every 10 meters requiring 12V at 1 Amp,
adding up to 10 Amps total.  Now I don't know that the ohms / meter
are for RG58U, but I seriously doubt that it can carry the net
current to deliver that power, and even if it does the ohmic drops
will be such that local regulators are needed, etc. etc.

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Re: Serial+power over single coax cable
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According to http://www.elpa.lt/eng/cables/coaxial/490503.html 34 Ohms/Km
inner conductor, 17 Ohms/Km outer conductor

So 5.1 Ohms round trip, or a 51V drop.  Unless I dropped a decimal point
somewhere. Of course most of the current doesn't go the full distance but
even at 1A there is a 5V dropand that estimate would be too optimistic.

No indication there of when you run into heating problems though.


Robert

Re: Serial+power over single coax cable
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Exactly.  Even if the current per station is cut to 0.1 A the
system is obviously hairy.  Any reasonable use would need local
DC/DC converters and regulators.  By this time you probably want to
increase the supply voltage (on the coax) to reduce current and
mitigate ohmic losses.  In any reasonable world that voltage is
limited to 48 V for safety reasons.

Of course if the coax run is only 10 meters total, the numbers
change.  But I don't think such a physically small overall system
warrants the complications of supplying power over the cable.

Once the OP settles these fundamental questions he can decide on
actual means of multiplexing data and power.

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Re: Serial+power over single coax cable
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RG58 is good for at least 500V, spec'ed for 2.5kV operating.
So this should leave some room for a switcher.

Rene
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Re: Serial+power over single coax cable

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The cable may be.  But I hope you're aware that in a lot of countries,
to go beyond around 48V, you'll need board-certified personnel to
install any cable routinely carrying that kind of voltage, aren't you?

Remember: legally, anything beyond about 48 volts is considered
dangerous, experts-only "high voltage".  Anybody without formal
certification ever having been allowed to fiddle with such a system is
thus considered gross neglect of duties, and loses all insurance
protection.

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Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Serial+power over single coax cable
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Is that the case of amateur radio operators as
well?  The RF voltages in a typical amateur radio
antenna lead could easily be in the 100's of
volts.



Re: Serial+power over single coax cable

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I think the legal situation appliesonly to products not persons.  if a
device uses voltages only below 48V (so called safety extra low) it makes
it easier for it to gain safety certification no matter what side of the
pond you are on.  Using higher voltages requires measures to ensure users
cannot be harmed by them before safety certification is granted - applies
to most all domestic mains operated appliances.

None of this applies to anything you make yourself at home.

Ian
--
Ian Bell

Was Serial+power over single coax cable now electrical safety

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My question was a bit of a troll for Hans-Bernhard.
The legal issues vary widely from place to place and
I am curious how amateur radio operators deal with
the regulations in Germany.

In my city, the saying is "you need a building permit
to drive a nail".  OTOH, they are extremely helpful
with homeowners that do the work themselves.  I drew
up plans for a 240 volt, 50 ampere subpanel in my
garage, had the chief building inspector sign off the
drawing, did the work, got it inspected and signed off
by the city for about $40 in fees.

The last city I lived in *required* all electrical work
to be done by a licensed electrician.














Re: Was Serial+power over single coax cable now electrical safety

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OK, so now you've admitted as much, I'll bite.

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I'm not a HAM, but us Germans being who we are ;-), it's bound to be
regulated by federal law just as strictly as electrical work is.
IIRC, HAM licensing is handled by a federal institution here (our
version of the FCC), and the exams before you get a license are pretty
heavy.

Well, this is Germany after all, possibly the only country in the
western world where the guilds still hold most of the same privileges
they did in the year 1400.  E.g. some local chapters of the guild of
electricians managed to sue computer/telekom system integrators out of
business, because they did "electrical installation" (as in: they
dared to lay network cables), but didn't have a guild "Meister" on
their payroll, without which it's forbidden to run such a business.

--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Was Serial+power over single coax cable now electrical safety

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I was stationed in Neu-Ulm in 1972, with the US
Army. Now that you mention it, I recall that even
on-base the power system had a very clear this-is-yours
/this-is-ours separation of what the tradespeople
handled and what we took care of.  I enjoyed several
pleasant days off while the local electricians took down
the power to do some "necessary" rewiring.

Between that and having worked several years with an old
immigrant German mechanical engineer, I've a fair
understanding of how your system works.

It may be a little inconvenient for engineering,
but it makes for fine beer (:



Re: Was Serial+power over single coax cable now electrical safety

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Well with anything directly to do with domestic mains wiring, things are
about to change in the UK with the introduction of Part P of the IEE wiring
regs which require all such work to be done by a (licensed) qualified
person.

However, anything you do to something that just plugs into the mains is
still regulation free though not hazard free ;-)

Ian

--
Ian Bell

Re: Serial+power over single coax cable
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And many hams have been killed or injured by their own rigs.

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