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What your mother didn't tell you about transmission lines

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Fred Townsend

What your mother didn't tell you about transmission lines

Was KPA500 RF output wiring:

Gary there are several distinctions:
First there is a difference between a jumper and a transmission line. For
short distances you will have perturbations at the start and finish that
will average out because you do not really establish the transmission line
effect. Losses are usually insignificant. So to make a twisted pair put two
insulated wires in your drill chuck and twist them together. Works great.
Things get very different when the distance moves out.

For twisted pair (TP) to be an effective transmission line the twist must be
constant. This is called Unified Twist Pair (UTP) Examples of UTP are CAT5
and CAT6 cable. If you twist it yourself the twist will not be constant so
you will get dispersion effects and other problems. Dispersion is usually
not too big a problem at HF but it does cause phase noise.

Rubber (parallel) lamp cord can be used as transmission line and it is
cheap. Z0 runs 95 to 120 Ohms depending on insulation thickness.
Z0, the surge impedance of coax runs 50 to 91 Ohms. (91 Ohm is pretty hard
to work with because the center conductor is so thin.)
Z0 runs 95 to 900 Ohms for twin lead but really widens out beyond 300 Ohms
(AKA ladder line).
The limits for both are determined by physics. You can push them but you
can't change them so in short there is no such thing as 50 Ohm twin lead or
300 Ohm coax.

Finally if you are making your own TP I suggest you use either Kynar or
Teflon insulated wire. Both will be silver plated and have lower losses than
copper.

73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Gary Hinson
Sent: Saturday, September 10, 2011 11:06 PM
To: [hidden email]
Subject: Re: [Elecraft] KPA500 RF output wiring

> Sure. Twisted pair is a VERY effective transmission line, and that is
> what is needed ...

Hey Jim, what kind of twisted pair could I use to feed my [mostly 50 ohm] HF
antennas? Coax is expensive in ZL so I'm willing to try alternatives. I'm
even thinking of homebrew balanced line with baluns at the bottom (a
coax-fed remote antenna switch in my case).

73
Gary ZL2iFB

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Bill W4ZV

Re: What your mother didn't tell you about transmission lines

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-Antenna/Zipcord-Antenna-7903031.pdf

73, Bill

Jack Smith-6

Re: 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-Antenna/Zipcord-Antenna-7903031.pdf
>
> 73, Bill
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/What-your-mother-didn-t-tell-you-about-transmission-lines-tp6780383p6780644.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Fred Townsend

Re: What your mother didn't tell you about transmission lines

In reply to this post by Fred Townsend

I should make two points that may not have been apparent from my sarcasm in
the subject line.
1. Zip cord is a last resort, not a first.
2. You still have to match the stuff and Z0 is a moving target. Matching can
mean baluns on one or both ends.

Was KPA500 RF output wiring:

Gary there are several distinctions:
First there is a difference between a jumper and a transmission line. For
short distances you will have perturbations at the start and finish that
will average out because you do not really establish the transmission line
effect. Losses are usually insignificant. So to make a twisted pair put two
insulated wires in your drill chuck and twist them together. Works great.
Things get very different when the distance moves out.

For twisted pair (TP) to be an effective transmission line the twist must be
constant. This is called Unified Twist Pair (UTP) Examples of UTP are CAT5
and CAT6 cable. If you twist it yourself the twist will not be constant so
you will get dispersion effects and other problems. Dispersion is usually
not too big a problem at HF but it does cause phase noise.

Rubber (parallel) lamp cord can be used as transmission line and it is
cheap. Z0 runs 95 to 120 Ohms depending on insulation thickness.
Z0, the surge impedance of coax runs 50 to 91 Ohms. (91 Ohm is pretty hard
to work with because the center conductor is so thin.)
Z0 runs 95 to 900 Ohms for twin lead but really widens out beyond 300 Ohms
(AKA ladder line).
The limits for both are determined by physics. You can push them but you
can't change them so in short there is no such thing as 50 Ohm twin lead or
300 Ohm coax.

Finally if you are making your own TP I suggest you use either Kynar or
Teflon insulated wire. Both will be silver plated and have lower losses than
copper.

73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Gary Hinson
Sent: Saturday, September 10, 2011 11:06 PM
To: [hidden email]
Subject: Re: [Elecraft] KPA500 RF output wiring

> Sure. Twisted pair is a VERY effective transmission line, and that is
> what is needed ...

Hey Jim, what kind of twisted pair could I use to feed my [mostly 50 ohm] HF
antennas? Coax is expensive in ZL so I'm willing to try alternatives. I'm
even thinking of homebrew balanced line with baluns at the bottom (a
coax-fed remote antenna switch in my case).

73
Gary ZL2iFB

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Gary Hinson

Re: What your mother didn't tell you about transmission lines

In reply to this post by Jack Smith-6

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: [hidden email]
> [mailto:[hidden email]] On Behalf Of Jack Smith
> Sent: Monday, 12 September 2011 1:01 AM
> To: [hidden email]
> 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.
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Guy, K2AV

Re: What your mother didn't tell you about transmission lines

A quick warning about actually using zip cord for feedline. The typical
insulation material is NOT designed for RF transmission, usually for
flexibility, color, durability taking the abuse that AC cords always take,
etc. It is almost always some PVC based formulation. Zip cord has been
famously LOSSY and wholly unsuitable for feedline. At one time I did see
some Polyethylene (PE) zip cord which may have been pretty decent.

I have constructed balanced feedline from tie-wrapped parallel teflon
insulated #12 silvered copper wire that can be found on eBay from time to
time. It seemed to measure a fairly reliable 84 ohms, and I have been able
to use that and ladder line for QRO transmission line transformers that hold
up well to Mother Nature. Just use the very small tie wraps (UV resistant
stuff) to keep the two wires together every six inches or so. I did NOT
twist the wire.

73, Guy

On Sun, Sep 11, 2011 at 3:27 PM, Gary Hinson <[hidden email]> wrote:

> 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: [hidden email]
> > [mailto:[hidden email]] On Behalf Of Jack Smith
> > Sent: Monday, 12 September 2011 1:01 AM
> > To: [hidden email]
> > 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.
> > > ______________________________________________________________
> > > Elecraft mailing list
> > > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > > Help: http://mailman.qth.net/mmfaq.htm
> > > Post: mailto:[hidden email]
> > >
> > > This list hosted by: http://www.qsl.net
> > > Please help support this email list: http://www.qsl.net/donate.html
> > >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Jim Brown-10

Re: What your mother didn't tell you about transmission lines

In reply to this post by Bill W4ZV

On 9/11/2011 5:20 AM, Bill W4ZV wrote:
> 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.

At HF, loss is essentially due to the resistance of the conductors, plus
whatever loss there might be due to mismatch. For matched loads, the
current is less with higher impedance lines, so the loss is less. Most
zip cord uses relatively small conductors. BTW -- have you ever noticed
that the Red/Black glorified zip cord sold at hamfests by CB radio
dealers is often smaller than it is marked? BIG insulation, very small
copper. Advertised #12, but try stripping it and taking a micrometer (or
ohmmeter) to it.

Let's compare it to RG58 can be pretty lossy too, depending on how much
copper was used to build it. At 10 MHz, the published loss data for
Belden RG58 cables varies from 1.1 to 1.5dB/100 ft. That loss is ALL due
to copper, and at 10 MHz, skin effect dominates. The shield in these
RG58 cables is a MUCH greater diameter than in the zip cord, so the loss
in the shield is a lot less than for the zip cord, which can be #18 or
smaller.

Another suggestion to our friend in ZL. Here in North America, cable TV
companies use millions of feet of 75 ohm 1/2-inch hard line.
Installation companies have no use for short lengths of cable, so it
goes in the trash, and short lengths to these guys is often several
hundred feet. If we make friends with our local CATV company, we are
often able to replace the word "trash" with the words "back of my
pickup." Loss data for this cable is roughly the same as for 50 ohm
hard line.

About two years ago, I inherited a very large spool of this stuff from a
SK. I am currently installing two monobanders for 20M and 15M on a new
tower, and have cut lengths of 1/2-inch hard line to feed both of them.
One of them is already operational and works great. If you google, you
will find excellent information about practical and technical details
for using this stuff in your ham station, including how to easily fit
PL259 connectors, and how to cut the cable to a whole number of half
wavelengths so that the impedance is not transformed by the cable. Some
very useful websites I found are by W9XT and N1GUN. There's also a nice
piece that ran in the VHF column of QST in 2000. Search the ARRL website
to find it. I'm in the process of putting together something myself
that shows loss data and an alternate method of installing PL259
connectors. I found another piece on the internet that correctly
observes that this coax can make stubs that are a bit higher Q than most
other available coax. Higher Q means greater attenuation, but also
narrower bandwidth for that attenuation.

73, Jim Brown K9YC
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