Antenna installation

[isw]

In article <ctcg081m6st57853hi8j3ehdrop5m87vru@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

On Thu, 19 Jul 2012 06:56:18 -0700 (PDT), klem kedidelhopper
captainvideo462009@gmail.com> wrote:

Never thought of using Romex for RF. It would indeed be interesting to
see what it's characteristic impedance would be at different
frequencies though.

Nope. It's quite constant. As I vaguely recall (and can't find my
notes), it's about 110 ohms between outside conductors for 14-2 NM-B.
There's nothing in the dielectric and insulation to absorb power, so
the impedance is going to be constant up through UHF frequencies.

The impedance may not change, but I'm pretty sure the insulation in
Romex is vinyl, and I'm pretty sure it has a serious loss factor above
HF. There's a good reason you see polystyrene, mylar, mica, glass, and
teflon capacitors, but not vinyl capacitors.

Isaac

 

[Jeff Liebermann]

On Thu, 19 Jul 2012 22:16:45 -0700, isw <isw@witzend.com> wrote:

In article <ctcg081m6st57853hi8j3ehdrop5m87vru@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

On Thu, 19 Jul 2012 06:56:18 -0700 (PDT), klem kedidelhopper
captainvideo462009@gmail.com> wrote:

Never thought of using Romex for RF. It would indeed be interesting to
see what it's characteristic impedance would be at different
frequencies though.

Nope. It's quite constant. As I vaguely recall (and can't find my
notes), it's about 110 ohms between outside conductors for 14-2 NM-B.
There's nothing in the dielectric and insulation to absorb power, so
the impedance is going to be constant up through UHF frequencies.

The impedance may not change, but I'm pretty sure the insulation in
Romex is vinyl, and I'm pretty sure it has a serious loss factor above
HF. There's a good reason you see polystyrene, mylar, mica, glass, and
teflon capacitors, but not vinyl capacitors.

Isaac

Romex is vinyl jacketed PVC. Not the best of insulation for RF. I
couldn't find a value for loss tangent, probably because it varies by
composition, manufacturer, color doping, position of the moon, etc.
<http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm>
You're probably right that it's not useful at UHF, but I'm too
lazy/busy to test it.

The ham doing the Romex testing was Dave Stoddart W8FLL (SK) who died
in 2008.
<http://www.k6bj.org/profiles/w8fll/>


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558