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OT: Routing coax near CAT5

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Craig Rairdin

OT: Routing coax near CAT5

So right now I run the coax from my HF antenna to a point just outside my
window. When I want to operate I crank open the window and connect the coax
from my rig to the end of the coax outside the window. I don't really have a
way to leave it hooked up all the time because I don't want to leave the
ground-level window partially open.

I want to run the coax into the house through the wall, up the inside of the
wall into the attic above my office, across the floor of the attic and down
the inside of a wall to an existing utility box that is where all my phone
and network connections are routed. This means I'll have coax running
alongside both phone and CAT5. Seems like a lot of RF.

I'm only running 100W. I suppose someday I might get some kind of amp but
it's not a priority. But I don't want to rule that out simply because of the
way I routed my antenna feedline.

I can choose a different routing for the feedline and terminate it in a
different box that's a few feet away from my CAT5 and phone lines, but I'd
prefer not to have to install a new box.

So my question is, is all that RF going to interfere with my network
connection or my phones? Any thoughts or recommendations?

Craig
NZ0R
KX1 #1499
K1 #1966
K2/100 #4941
K3/100 < #200

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Vic K2VCO

Re: OT: Routing coax near CAT5

Craig Rairdin wrote:

> So my question is, is all that RF going to interfere with my network
> connection or my phones? Any thoughts or recommendations?

If the coax is properly decoupled from the antenna there will be no RF
on the outside of it. So it will be no more likely to interfere with
anything than a water pipe.

'Properly decoupled' means that if you are feeding a dipole, for
example, there should be a balun at the feedpoint and the coax should
come away from the antenna at right angles to the elements for as far as
possible. A vertical should also have a choke or bead balun at the
feedpoint.

Finally, if the coax does not run at a right angle for enough distance
('right angle' and 'enough distance' are relative to how much RF on the
outside of the coax you can tolerate), you can add a choke or bead balun
right outside the box.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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Don Wilhelm-3

Re: OT: Routing coax near CAT5

In reply to this post by Craig Rairdin

Craig,

Theoretically, there should be no radiation outside the coax shield, so
you would not have a problem.

Practically, you may have common mode currents on the outside of your
coax (that is a bad thing), so it would be prudent to install an in-line
isolator (same thing as a 1:1 current balun) at the point where the coax
enters the building. Provide a ground path for the current to flow - a
good low impedance ground, and connect the antenna side of the isolator
(and coax shield) to the ground.

Lightning protection at the entry point to the dwelling is also prudent
- PolyPhaser or other reliable brand of lightning suppressor devices are
good. Consider that you may have to defend your choice of protective
devices to your insurance adjuster if you ever have a claim involving
the feedline entry.

73,
Don W3FPR

Craig Rairdin wrote:

> So right now I run the coax from my HF antenna to a point just outside my
> window. When I want to operate I crank open the window and connect the coax
> from my rig to the end of the coax outside the window. I don't really have a
> way to leave it hooked up all the time because I don't want to leave the
> ground-level window partially open.
>
> I want to run the coax into the house through the wall, up the inside of the
> wall into the attic above my office, across the floor of the attic and down
> the inside of a wall to an existing utility box that is where all my phone
> and network connections are routed. This means I'll have coax running
> alongside both phone and CAT5. Seems like a lot of RF.
>
> I'm only running 100W. I suppose someday I might get some kind of amp but
> it's not a priority. But I don't want to rule that out simply because of the
> way I routed my antenna feedline.
>
> I can choose a different routing for the feedline and terminate it in a
> different box that's a few feet away from my CAT5 and phone lines, but I'd
> prefer not to have to install a new box.
>
> So my question is, is all that RF going to interfere with my network
> connection or my phones? Any thoughts or recommendations?

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Ron D'Eau Claire-2

RE: OT: Routing coax near CAT5

In reply to this post by Craig Rairdin

If it's good coax and you take some simple measures to ensure RF currents on
the *outside* are suppressed, there should be no problem at all, either
injecting xmit RF into other circuits or picking up noise from them. That
sort of thing is done all the time in commercial layouts.

Good coax has dense shield. Cheap coax may have rather loose shielding
covering perhaps only 70% or 80% of the inner conductor's insulation. That
allows leakage of RF in and out of the shield. Normally it's not enough to
cause real trouble, but when you want good shielding you need a good, dense
shield. Coax braid should cover well over 90% of the center conductor.

Since RF travels on the skin of the conductor, the RF currents on the
outside surface of the shield are completely isolated from those on the
inside surface (assuming it's good shield). In most Ham installations, RF
currents on the outside are hard to avoid, since the end of the coax near
the antenna is very close to it! When feeding a balanced radiator, like the
center of a dipole, it's often recommended that the coax run away from the
antenna at exactly right angles for at least 1/4 wavelength. That's to
minimize RF currents on the outside of the coax shield. Strong currents will
be induced on the outer shield by the close proximity of the antenna
carrying strong RF currents, but, if the coax runs away at exactly right
angles, the currents induced in the shield by one side of the antenna will
be exactly balanced by the 180 degree out-of-phase currents on the other
side of the antenna and no net current will flow on the outside of the
shield.

Some guys are lucky, but I easily can count the number of times I've been
able to do that at home in the HF range: zero!

The currents flowing on the outside of the coax can be suppressed though,
using ferrite beads that slip over the coax (the famous W2AU balun is just
such a device) or coiling the coax into an inductor of sufficient size to
choke off the currents. If you do that where the coax enters your home, you
should not have significant currents on the outside to bother any other
electronics.

Ron AC7AC

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Craig Rairdin

So right now I run the coax from my HF antenna to a point just outside my
window. When I want to operate I crank open the window and connect the coax
from my rig to the end of the coax outside the window. I don't really have a
way to leave it hooked up all the time because I don't want to leave the
ground-level window partially open.

I want to run the coax into the house through the wall, up the inside of the
wall into the attic above my office, across the floor of the attic and down
the inside of a wall to an existing utility box that is where all my phone
and network connections are routed. This means I'll have coax running
alongside both phone and CAT5. Seems like a lot of RF.

I'm only running 100W. I suppose someday I might get some kind of amp but
it's not a priority. But I don't want to rule that out simply because of the
way I routed my antenna feedline.

I can choose a different routing for the feedline and terminate it in a
different box that's a few feet away from my CAT5 and phone lines, but I'd
prefer not to have to install a new box.

So my question is, is all that RF going to interfere with my network
connection or my phones? Any thoughts or recommendations?

Craig
NZ0R
KX1 #1499
K1 #1966
K2/100 #4941
K3/100 < #200

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Brian Lloyd-6

Re: OT: Routing coax near CAT5

> So my question is, is all that RF going to interfere with my network
> connection or my phones? Any thoughts or recommendations?

So far everyone has addressed the issue of your rig interfering with
your phone and your network so I won't spend much time on that except
to add that, even if there is RF on the outside of the coax it
probably isn't going to cause a problem with your networking gear as
that uses twisted-pair and RF would show up as common-mode cruft
which will get canceled out in the ethernet coupling transformers.

OTOH, RF noise from your networking equipment might get coupled to
your feedline. Remember you are trying to listen to very weak signals
and ethernet, while well-crafted so as not to radiate, does leak just
a little. I would probably choose to route my feedline away from my
ethernet wiring just to reduce noise pick-up in your rig.

73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com

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Ron D'Eau Claire-2

RE: OT: Routing coax near CAT5

John, NO8V brought a typo to my attention. I said W2AU instead of W2DU
balun. There more info about the W2DU ferrite bead balun at:

http://www.w2du.com/r2ch21.pdf

Thanks, John!

Ron AC7AC

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Vic K2VCO

Re: OT: Routing coax near CAT5

In reply to this post by Brian Lloyd-6

Brian Lloyd wrote:

> OTOH, RF noise from your networking equipment might get coupled to your
> feedline. Remember you are trying to listen to very weak signals and
> ethernet, while well-crafted so as not to radiate, does leak just a
> little. I would probably choose to route my feedline away from my
> ethernet wiring just to reduce noise pick-up in your rig.

A balun at the antenna would help with this too. RF from the network
(and other local sources) will run up the outside of the feedline; a
balun at the top will choke it off so it does not get to the antenna and
flow back to your receiver.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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Chris Kantarjiev K6DBG

RE: OT: Routing coax near CAT5

In reply to this post by Craig Rairdin

If you've got 100Mbps Ethernet in your house, you're probably already
hearing noise around 14.031, unless your antenna is far, far away
from your networking equipment. It's not just the cables, but also
the routers and interface cards that seem to spew this stuff!

For a nice discussion of common mode currents and what to do about
them, I like the paper by Chuck W1HIS at

http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf

Fair-rite makes a snap-on ferrite, p/n 0443164151, which snaps
comfortably over three turns of RG-8X. I use two of them to
make a choke at the point where my coax enters the house through
a window, as well as a coil-wound balun/choke at the base of
my vertical. This seems to handle the common mode problems well
(but my vertical still picks up all kinds of RF from the neighborhood!)

DXEngineering has similar snap-on ferrites in various sizes, too.

73 de chris K6DBG
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ac0h

Re: OT: Routing coax near CAT5

In reply to this post by Craig Rairdin

- --
R. Kevin Stover, ACØH
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