Discussion in 'General Technical Questions and Answers' started by KC9GUZ, Sep 15, 2006.
I had a local tell me he once made a dipole using lamp cord as the feedline. Has anyone tried this?
it may work to some degree, but I think the spacing might be too close for some things.
Yip. It's not the lowest loss stuff in the world, but I've used it for portable operation. It's about 75 ohms.
was in common use over 50 years ago
its a balanced feed line same as open wire
only closer spacing
with more line loss
and lower imp about 75 ohms
works ok on lower bands
line losses get you above 40 meters
remember you can use most
any kind of wire for a feedline
and you can bet its been tryed
ive used junk small gage
twisted pair telephone wire for
feed line on a 80 meter dipole
it worked fb
Twisted pair can be very low loss up to >600 MHz if it's twisted right.
CAT-6e, for example, is nothing more than twisted pairs and is rated to 600 MHz. It contains radiation very well and maintains constant impedance up to about that frequency, without shielding.
"Any old" twisted pair works pretty well on HF.
Yup, the answer has been pretty well given, but this question does come up occasionally. Another thing about lamp wire is that some of it is not the least bit resistant to Ultra-Violet. The insulation will crack and break off after just a very short time of exposure to the elements. But as has been said, for portable, short-term operation on the low bands, it is useable!
Ladder line is a far more suitable alternative, can be rolled up into a fairly small bundle, and works at much lower loss if you are planning to use it either on a higher band, or for a more permanent installation.
Good luck! 73, Jim
Seems I've read that the impedance runs something like 35 ohms. It sure is easy to handle.
73, JP, K8AG
Like every other transmission line, the impedance would vary as a relationship between wire spacing, and wire size. In other words, a piece of 16 gauge lightweight lamp cord would have a different impedance than a piece of 12 gauge heavyweight extension cord!
The impedance of the cord would not be all that much of a factor, though, because you would probably be feeding the antenna through a balun/tuner setup, and unless you went really wild with the thing ( 10 feet of dipole on 160 meters ! ) and you are able to match the setup to the rig, you will be able to use it. However , as Mac and others have stated, the losses DO increase with frequency, as the stuff is just not all that good at RF. After all, it was made to transfer 60hz AC , not RF!
Yep. Used lamp cord (known popularly as "zip cord" for several antennas and feedlines over the years. Once had a 75 meter dipole made of zip cord, and fed with zip cord, from a link-coupled transmitter. Worked wonderfully. I have no idea what the impedance was! Or the SWR. All I know is my weak (20 watts input, Central Electronics 20A barefoot, couple thorugh a homemade tuner) got out very nicely.
Go for it.
Yeah, I imagine the modern plastics used in zip cord are a LOT better than the old rubber of yore. Probably almost as good as "official" twin lead.