Using twin wire telephone wire?

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Don Bukar:
I have two questions and after doing a search have not found the answer that helps me so I am again asking for help.
   I have a large amount of telephone company phone wire that I would like to use as a center-fed dipole. (a), I see that others have used this wire but mine has TWO wires running parallel inside the very tough insulation. Will this cause some kind of parasitic situation and/or (b), should I solder the two wires together when I connect them at the center of the dipole?
   
   I don't seem to be able to get a picture in my mind about the feedline coming from the center connector of the dipole. I think that I have read that it should be at a 90 deg. angle from the long axis of the antenna but for how far? In other words, can I run it over head from the tree hung antenna at a 90 deg. angle for about 30 feet, attach it to the house (log with a steel roof) and then make turns around the house corners to get into the basement shack? Or, should I only drop the feed straight down and then shoot off at some angle in a buried pipe to the shack. I am hoping to hang the center of the antenna at about 45-50 feet with the ends having to be about 15-20 feet off the ground.
   Info and opinions are welcome. By the way, I will be trying to transmit with a FT-101EX and a MFJ tuner when I get my General ticket; just listening with it on a simple long wire now.

Steve Katz:
Use both wires, just twist them together at each end.

Use a good, strong center insulator and good end insulators at each end of the antenna.  Most telephone "insulated twisted pair" line is pretty strong and unless you're making a very long dipole it should survive.

I've used the "house drop" telco lines for wire antennas lots of times, but all the stuff I've used is a lot more than "one" twisted pair!  It's usually about 20 twisted pairs, so there's a lot of conductors in there.  I strip them all and twist them all together at each end.  Each wire is quite thin, maybe #22 or #24, but when you parallel a pile of them it's pretty strong.  And the insulation is tough as nails, the phone companies know what they're doing to avoid having to service stuff for 20+ years at a time.

You can take many routes with transmission lines, but your last suggestion about running the coax down to the ground and then burying it (or something) to get to the house almost always works best because it helps assure the antenna won't couple into the coax -- which is undesirable about 100% of the time.

Owen Duffy:
I might add to Steve's response that in your case, whilst new cable is quite strong, the amount of copper is small and dipole copper losses will be higher than using a more substantial copper conductor.

I said new cable, because if the cable you have does not have a steel messenger wire, and the copper is pure copper (not copper clad steel), the strength will degrade seriously if it cracks in service. Most bride cables or drop cable designed for aerial rigging have an integral steel messenger wire. This may be a drop cable intended for underground use.

There are some wires that are very suited to wire antennas, and most opportune substitutes turn out to be pretty poor ones if you want a long lasting antenna with good performance. Good wire lasts a long time, I reuse it and reuse it. My preferences are 1.6mm gal fence wire for prototypes, and 2mm hard drawn copper for permanent installations. You have access to Copperweld which I don't, it is also a good choice for many purposes.

Owen

Don Bukar:
I should have included this info: I got this wire about 25 years ago when the phone company was replacing what I will refer to as "main-line" along a major road between two fair sized cities. I knew it was very high tensile strength but not why until now, I just did a spark test and both 16 gauge wires are copper coated steel. The insulation is so tough it is hard to cut it with a sharp razor.I have used some of this to pull a truck out of the mud in the past!
I don't have to use this stuff, I just thought it would be fun to use old Bell System wire to communicate with the world. You know, Old radio/Old wire. I knew it was strong,too.
I am studying about antennas and as you know, a little knowledge can be a dangerous thing! LOL! I am thinking about what would result if I used this wire as a feed line to coax at the out side of the shack concrete wall? Would the feed line become a hinderance to the arms of the dipole? I know that this is the same wire they bury from pole to house.

Owen Duffy:
Quote from: KJ4RQV on March 06, 2010, 01:58:07 PM

...I am thinking about what would result if I used this wire as a feed line to coax at the out side of the shack concrete wall? Would the feed line become a hinderance to the arms of the dipole? I know that this is the same wire they bury from pole to house.


What is the insulation? If it is PVC, it will make a relatively poor open wire feed line (assuming you mean using the pair as an open wire feed line), and in any event, a relatively low Zo open wire line which will be relatively lossy for the copper (CCS) diameter.

Using it for the dipole wires as Steve described should be OK, I would not use it for feedline.

Owen

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