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Author Topic: Long/Random Wire with Twisted Pair - Untwist or Not?  (Read 3546 times)

Offline R4002

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with Twisted Pair - Untwist or Not?
« Reply #15 on: September 06, 2017, 1517 UTC »
I would think that the individual wires from a Cat 5 cable would be too thin to really hold their own (mechanically or physically speaking) against wind, squirrels, etc (when used as a random wire or long wire antenna). 

Chris is likely right here, the outer jacket would probably be more helpful than hurtful.  You can get speaker hookup wire or "zip wire" for super cheap on Internet sites like eBay and Amazon and not have to worry about the wire breaking the first time a storm comes through. 
U.S. East Coast, various HF/VHF/UHF radios/scanners/receivers

Offline redhat

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Re: Long/Random Wire with Twisted Pair - Untwist or Not?
« Reply #16 on: September 07, 2017, 0312 UTC »
Agreed, cat5 although made of the right stuff, is likely too weak to hold itself under tension for long.  The jacket will also break down from the sun's UV and all the insulation will come off in a few years.  I would think you'd be better off with #14 house wire for tension type service.

FWIW, i recently made a small AM receiving loop out of some scraps of cat5 for a radio station so they could monitor their off air feed.  shorting the pair wires together and alternating pairs made for basically a 4 turn loop.  Slap a ferrite on each end of another piece of cat5 using one pair and it worked surprisingly well.

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Offline ultravista

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Re: Long/Random Wire with Twisted Pair - Untwist or Not?
« Reply #17 on: September 07, 2017, 1335 UTC »
Thanks for the feedback. I don't plan this as a permanent solution, just something I can string-up and get on the air. Once I find a working solution, it will be built better & stronger.

Can you share the full design for the receiving loop? Each pair was sorted @ each end and all four pairs were used?

>> Slap a ferrite on each end of another piece of cat5 using one pair and it worked surprisingly well ???

Offline redhat

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Re: Long/Random Wire with Twisted Pair - Untwist or Not?
« Reply #18 on: September 07, 2017, 2330 UTC »
http://www.mile204.us/PotsdamDan/RubeGoldberg/Ultimate_AM.html

This is the basic idea, except mine was made out of a 3' piece of cat5 with each pair's conductors shorted together and then wired alternatingly to produce a four turn loop.  I just hung mine on the wall with push pins and used another 6' scrap piece of cat 5 with the white/blue pair tied to the output of the loop.  The receiver I was feeding it with had an unbalanced input, so I placed a high permiability ferrite snap-on core at the receive end to make a crude balun.  The transmitter was only a few miles from the building so just about anything would have worked, but I needed to keep the electrical noise out of the AM audio, and a loop is a good way to do that.

+-RH
Somewhere under the stars...
WinRadio Excalibur/305 w/ a chi-town resonant loop, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Online Ray Lalleu

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Re: Long/Random Wire with Twisted Pair - Untwist or Not?
« Reply #19 on: September 28, 2017, 2204 UTC »
If you have a length of twisted pair cable, just untwist an end to get the two arms of a dipole (horizontal, far from house), then run the twisted part to your shack window (at exact right angle to the dipole for as long as possible, to get the best balancing), then use a differential ATU to tune the whole thing to any SW frequency. Typical length of wire (including the dipole and both wires of the line) should be about 3 half wavelengths (for exemple), but the coils in the ATU can change this widely).

In fact, this is the doublet antenna, tunable to almost any frequency by the ATU at your hand near the receiver. Instead, the total length maybe about 5 or 7 half wavelengths, or only 1 wavelength (for example on 75m and close to the house). The twisted line can be coiled near the house entrance and/or near the central pole to better fight the common mode.

Wrong questions: the complex impedance of the doublet, the characteristic impedance of the line. The right question is to tune the full assembly of the doublet + the bifilar line + the ATU with an odd number of half wavelengths (approx.).

 I tried the doublet years ago, when my large horizontal loop broke down, just using the remnants, and got immediately much better DX results. Thinking back, maybe a part of the not so good "sky hook" results was due to the line not in the symetry plane of the loop (it was easier with the remnants to place the line just at equal distances from both arms), but the doublet has also a better differential behaviour (the ends are nodes!), and is easier to place far from the house.

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Offline ultravista

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Re: Long/Random Wire with Twisted Pair - Untwist or Not?
« Reply #20 on: September 29, 2017, 0404 UTC »
Thank you Ray