[Elecraft] What your mother didn't tell you about transmission lines

[Gary Hinson]

Thanks guys.

I've made open wire/ladder line before and will be doing so again for a
planned vee-beam array, but I've never tried twisted pair other than UTP for
Ethernet (most people call it "Unshielded Twisted Pair" but I guess
"Unified" or "Uniform" would make sense too).  

Years ago I used copper zip cord/bellwire for make-shift portable dipoles
(just knotted the centre point to stop it all unzipping!) - worked well
enough with an outboard toroidal balun and ATU in the K2 for a few QSOs
while on holiday in the South of France.  There were better things to do
than play radio!

The 120 ohm impedance of zip cord should be a close-enough match for a
fullwave loop.  

73,
Gary  ZL2iFB


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jack Smith
> Sent: Monday, 12 September 2011 1:01 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] What your mother didn't tell you 
> about transmission lines
> 
> A few years ago, I measured a length of plastic (some form of 
> vinyl, I 
> believe) insulated zip cord with the loss results below.
> 
> Impedance over the range 300 KHz - 30 MHz varied from 118 
> ohms to 124 ohms.
> 
> Jack K8ZOA
> 
> 
> Frequency MHz 	Loss (dB)/100 ft
> 5 	2.3
> 10 	3.5
> 15 	4.6
> 20 	5.5
> 25 	6.9
> 30 	8.1
> 35 	8.7
> 40 	9.2
> 45 	10.4
> 50 	11.6
> 
> 
> 
> On 9/11/2011 8:20 AM, Bill W4ZV wrote:
> > Fred Townsend wrote:
> >> Rubber (parallel) lamp cord can be used as transmission 
> line and it is
> >> cheap. Z0 runs 95 to 120 Ohms depending on insulation thickness.
> >>
> > True, but it has very high loss (especially at higher 
> frequencies) and
> > should only be considered as a last resort.  About 10 years 
> ago ET3PMW was
> > attempting to get on the low bands and only had zip cord 
> available for
> > transmission line.  I thought it should work fine for 80 
> and 160.  However,
> > on 80m running 100 watts he was barely detectible here using a 1200'
> > Beverage for receive.  Once Paul got some good ladder line, 
> his signal was
> > typically S8 on 80m and S6 on Topband, where he made 
> several hundred QSOs
> > with North America even in summer QRN (June/July).
> >
> > There is a loss graph on page 2 below but I believe 
> ET3PMW's losses were
> > much higher.  Of course this could have been due to poor 
> quality wire
> > available in Ethiopia.
> >
> > 
> http://www.we0h.us/Amateur_Radio_stuff/Antenna/ZIP-Cord-Antenn
a/Zipcord-Antenna-7903031.pdf
> >
> > 73,  Bill
> >
> >
> > --
> > View this message in context: 
> http://elecraft.365791.n2.nabble.com/What-your-mother-didn-t-t
ell-you-about-transmission-lines-tp6780383p6780644.html
> > Sent from the Elecraft mailing list archive at Nabble.com.
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