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OT: Feedline Question

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k3hx@juno.com

OT: Feedline Question

Message: 4
Date: Tue, 18 Apr 2017 03:31:59 +0000 (UTC)
From: Al Lorona <[hidden email]>
To: "[hidden email]" <[hidden email]>
Subject: Re: [Elecraft] OT; Feedline question
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=UTF-8

If instead of using the relative permittivity of air, 1.00059, for calculations of open-wire line, you use the effective permittivity including any spacers used to homebrew the line, this value will increase slightly.

For instance, I am using spacers made of a material called "nylon 6,6 30% glass fiber-reinforced" which happens to have a relative permittivity of 3.9. This has the effect of increasing the effective permittivity between the wires from 1.00059 to 1.08656. Another way of saying this is that the velocity factor goes from 1 (for pure air) to 0.959, or about 96% with the spacers. The effect of this is to make the characteristic impedance of the line drop from around 480 to around 460 ohms.

( See http://www.emclab.cei.uec.ac.jp/xiao/Wire/index.html )

This obsessive exercise on my part illustrates that spacers don't make a whole lot of difference, but they do make a difference. You may want to include their effect or not.

Al W6LX OM Al, Thank you for taking the time to share your results on this forum.
"That which is not rigorous is meaningless.".......Attributed to Blaise Pascal The results may not be significant or even of minor interest to many, but how would we know had this work not be done and presented here. 72, Tim Colbert K3HX
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Guy Olinger K2AV

Re: OT: Feedline Question

The effect of spacers is a very complex equation. One large modifier to the
end result is the number of spacers per unit of length. Then there is the
issue that the relative permittivity in between spacers reverts to air away
from the spacer. Then there is the area on either side of a spacer where
the effective permittivity blends from that of the spacer to that of air.

Then there is the loss based on number of spacers and loss tangent of the
spacer material modifying the lesser air loss.

Beyond that there is this peculiar ham inclination to use indoor insulated
electrical wire (THHN - rated dry indoors inside conduit only, 600 volts at
60 Hz) for QRO outdoor RF purposes. E.g.
https://www.73cnc.com/product_p/ls31.htm

Figure the wildly variant composition of PVC insulation at manufacture
followed by years of deteriorating UV outdoors.

In the end it is far easier to construct a feedline with a scientific guess
to obtain a target Z zero and then measure and adjust design to hit it on
the head and/or reduce its loss.

In practice there is little difference between 400 and 450 that is not
soaked up by all the tuner or circuitry finaglement we must engage in to
convert a wild range of Z to the narrow, narrow range actually tolerated by
our transistor finals.

Wireman for years has been selling various window lines we all
euphemistically call "450 ohm" which in fact vary between 360 and 440 ohm Z
zero. The reason for the variance is the spacing on all those lines is
identical regardless of the variation in wire diameter.

The constant wire diameter reduces the manufacturing setup and run costs
passed on to a cheep penny pinching ham population. [I include myself as
afflicted by this penny-pinching malaise. I just try to keep this nearly
irresistible inclination from dragging me into stupidity, as it has already
done on some number of occasions.]

73, Guy K2AV

On Tue, Apr 18, 2017 at 11:00 AM, [hidden email] <[hidden email]> wrote:

>
>
> Message: 4
> Date: Tue, 18 Apr 2017 03:31:59 +0000 (UTC)
> From: Al Lorona <[hidden email]>
> To: "[hidden email]" <[hidden email]>
> Subject: Re: [Elecraft] OT; Feedline question
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset=UTF-8
>
> If instead of using the relative permittivity of air, 1.00059, for
> calculations of open-wire line, you use the effective permittivity
> including any spacers used to homebrew the line, this value will increase
> slightly.
>
>
>
> For instance, I am using spacers made of a material called "nylon 6,6 30%
> glass fiber-reinforced" which happens to have a relative permittivity of
> 3.9. This has the effect of increasing the effective permittivity between
> the wires from 1.00059 to 1.08656. Another way of saying this is that the
> velocity factor goes from 1 (for pure air) to 0.959, or about 96% with the
> spacers. The effect of this is to make the characteristic impedance of the
> line drop from around 480 to around 460 ohms.
>
> ( See http://www.emclab.cei.uec.ac.jp/xiao/Wire/index.html )
>
> This obsessive exercise on my part illustrates that spacers don't make a
> whole lot of difference, but they do make a difference. You may want to
> include their effect or not.
>
> Al W6LX OM Al, Thank you for taking the time to share your results on
> this forum.
> "That which is not rigorous is meaningless.".......Attributed to Blaise
> Pascal The results may not be significant or even of minor interest to
> many, but how would we know had this work not be done and presented here.
> 72, Tim Colbert K3HX
> ____________________________________________________________
> "Better Than Adderall" Pill Now Legal For Your State Residents
> Health Tips Daily
> http://thirdpartyoffers.juno.com/TGL3131/58f62a48922102a474f94st04duc
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

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Jim Brown-10

Re: OT: Feedline Question

On Tue,4/18/2017 10:10 AM, Guy Olinger K2AV wrote:
> Then there is the loss based on number of spacers and loss tangent of the spacer material modifying the lesser air loss.

Below UHF, loss in transmission line is virtually all due to copper
losses unless the dielectric material is wet or is otherwise made
conductive.

Quite a few years ago, N6WS did some excellent work showing that losses
in window line are greatly increased when it is wet. His work was
published in QST and later included in Antenna Compendium #6. It should
be required reading for anyone considering window line. He measured four
types of window line and some open wire line he built himself. Putting
some numbers to it, Wes's measurements showed loss at 50 MHz increased
from about 0.4 dB/100 ft to more almost 6 dB/100 ft when it was wet. The
open wire line showed no increased loss when wet.

73, Jim K9YC

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Guy Olinger K2AV

Re: OT: Feedline Question

Hi, Jim,

What you appear to refer to by "open wire line" is BARE wire with small
spacers widely separated. Performance changes a lot if the "open wire line"
is constructed with unstripped THHN. Particularly with surface tension on
new THHN. Where hung on the level in a misting rain, I have seen a droplet
per centimeter hanging on THHN insulation. Along with a rather large
variation in Z as seen in the shack.

Just one more reason to keep to bare wire. Bare wire sloughs rain.

I remember 300 ohm TV open wire line from bare #18 copperweld with molded
spacers every three inches.

The 300 ohm ladder line if run near a furnace or fireplace flue would "go
bad" on TV channel 2 as well as the UHF channels. There was also this
phenomenon called acid rain which could severely modify electrical
behavior, including etching the copper conductors.

With the PE formed 300 ohm line, the reduction in signal strength could be
blamed on "the rain", which was true in one sense. But since it got better
when it dried up, the PE supported balanced line would never get the blame.

73, Guy K2AV

On Tue, Apr 18, 2017 at 1:37 PM, Jim Brown <[hidden email]>
wrote:

> On Tue,4/18/2017 10:10 AM, Guy Olinger K2AV wrote:
>
>> Then there is the loss based on number of spacers and loss tangent of the
>> spacer material modifying the lesser air loss.
>>
>
> Below UHF, loss in transmission line is virtually all due to copper losses
> unless the dielectric material is wet or is otherwise made conductive.
>
> Quite a few years ago, N6WS did some excellent work showing that losses in
> window line are greatly increased when it is wet. His work was published in
> QST and later included in Antenna Compendium #6. It should be required
> reading for anyone considering window line. He measured four types of
> window line and some open wire line he built himself. Putting some numbers
> to it, Wes's measurements showed loss at 50 MHz increased from about 0.4
> dB/100 ft to more almost 6 dB/100 ft when it was wet. The open wire line
> showed no increased loss when wet.
>
> 73, Jim K9YC
>
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

Jim Brown-10

Re: OT: Feedline Question

On Tue,4/18/2017 11:26 AM, Guy Olinger K2AV wrote:
> What you appear to refer to by "open wire line" is BARE wire with
> small spacers widely separated.

That's what Wes built to compare with the window line. Most practical
implementations of open wire line use much wider spacing. The increased
loss that Wes measured was due to water on the un-windowed parts of the
window line -- in other words, a significant fraction of the dielectric
between the conductors was water. That would not be true of widely
spaced wire, insulated or not.

73, Jim

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Brian D

Re: OT: Feedline Question

In reply to this post by Guy Olinger K2AV

What difference does oxidisation make on bare wire, ot tinning?? My feeders
are mainly enamelled copper which won't corrode. Does the enamel make a
significant difference? Hs anyone done the comparisons?

Guy Olinger K2AV <[hidden email]> wrote:

> What you appear to refer to by "open wire line" is BARE wire with small
> spacers widely separated. Performance changes a lot if the "open wire
> line" is constructed with unstripped THHN. Particularly with surface
> tension on new THHN. Where hung on the level in a misting rain, I have
> seen a droplet per centimeter hanging on THHN insulation. Along with a
> rather large variation in Z as seen in the shack.

--
Brian Duffell Yarm England
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Wes Stewart-2

Re: OT: Feedline Question

In reply to this post by Jim Brown-10

I'm cursed. It's bad enough that I've worked (I thought) several stations in DX
pileups only to later have the DX say, "Nope, we worked N6WS, not N7WS". Now my
work is attributed to him too. (Just kidding Jim)

Actually, the article never appeared in QST. Too technical; it went right to
the Antenna Compendium. And as a caveat, I never intended the "wet" numbers to
take on mythical properties. Water most definitely negatively affects ladder
lines (or as our European friends say, "chicken ladder line") but it's really
really difficult to quantify with precision.

I never did get around to testing the piece of Wireman line that my friend
Danny, K6MHE, sent me that was covered in moss. Living among Redwood trees is
considerably different from living among Saguaro Cactii.

Wes, the real N7WS

On 4/18/2017 10:37 AM, Jim Brown wrote:

> On Tue,4/18/2017 10:10 AM, Guy Olinger K2AV wrote:
>> Then there is the loss based on number of spacers and loss tangent of the
>> spacer material modifying the lesser air loss.
>
> Below UHF, loss in transmission line is virtually all due to copper losses
> unless the dielectric material is wet or is otherwise made conductive.
>
> Quite a few years ago, N6WS did some excellent work showing that losses in
> window line are greatly increased when it is wet. His work was published in
> QST and later included in Antenna Compendium #6. It should be required reading
> for anyone considering window line. He measured four types of window line and
> some open wire line he built himself. Putting some numbers to it, Wes's
> measurements showed loss at 50 MHz increased from about 0.4 dB/100 ft to more
> almost 6 dB/100 ft when it was wet. The open wire line showed no increased
> loss when wet.
>
> 73, Jim K9YC

Phil Wheeler-2

Re: OT: Feedline Question

Hey, and it looks like you are really in 7-land, Wes!

OTOH, I'm the "real W7OX", live in a suburb of Los
Angeles and have not lived in 7-land (OR/WA) since
1960; farthest North was Palo Alto when I was at
Stanford 1963-65. But 20 years ago we considered
retiring to Portland very seriously, so I used the
Gates to get back my original call -- W7UOX -- and
then shorten it to W7OX.

I like having the call for old times sake. But I
do wish the prefixes had call area geographic
meaning as they did in olden days.

73, Phil W7OX

On 4/18/17 12:57 PM, Wes Stewart wrote:

> I'm cursed. It's bad enough that I've worked (I
> thought) several stations in DX pileups only to
> later have the DX say, "Nope, we worked N6WS,
> not N7WS". Now my work is attributed to him
> too. (Just kidding Jim)
>
> Actually, the article never appeared in QST.
> Too technical; it went right to the Antenna
> Compendium. And as a caveat, I never intended
> the "wet" numbers to take on mythical
> properties. Water most definitely negatively
> affects ladder lines (or as our European friends
> say, "chicken ladder line") but it's really
> really difficult to quantify with precision.
>
> I never did get around to testing the piece of
> Wireman line that my friend Danny, K6MHE, sent
> me that was covered in moss. Living among
> Redwood trees is considerably different from
> living among Saguaro Cactii.
>
> Wes, the real N7WS
>
> On 4/18/2017 10:37 AM, Jim Brown wrote:
>> On Tue,4/18/2017 10:10 AM, Guy Olinger K2AV wrote:
>>> Then there is the loss based on number of
>>> spacers and loss tangent of the spacer
>>> material modifying the lesser air loss.
>>
>> Below UHF, loss in transmission line is
>> virtually all due to copper losses unless the
>> dielectric material is wet or is otherwise made
>> conductive.
>>
>> Quite a few years ago, N6WS did some excellent
>> work showing that losses in window line are
>> greatly increased when it is wet. His work was
>> published in QST and later included in Antenna
>> Compendium #6. It should be required reading
>> for anyone considering window line. He measured
>> four types of window line and some open wire
>> line he built himself. Putting some numbers to
>> it, Wes's measurements showed loss at 50 MHz
>> increased from about 0.4 dB/100 ft to more
>> almost 6 dB/100 ft when it was wet. The open
>> wire line showed no increased loss when wet.
>>
>> 73, Jim K9YC

Wes Stewart-2

Re: OT: Feedline Question

Yes, just like the bio (https://qrz.com/db/N7WS) says; been here 70 years. I
like to say I was conceived here, since my parents met and married in Tucson,
but were actually in San Diego when I was born. They moved back when I was a
young child and I've never left. No reason to, unless I want a chip shot to
SV/A, instead of,
I'll-never-live-long-enough-to-work-this-guy-through-the-east-coast.

Wes, N7WS, ex KN7CVT, K7CVT

.On 4/18/2017 1:24 PM, Phil Wheeler wrote:

> Hey, and it looks like you are really in 7-land, Wes!
>
> OTOH, I'm the "real W7OX", live in a suburb of Los Angeles and have not lived
> in 7-land (OR/WA) since 1960; farthest North was Palo Alto when I was at
> Stanford 1963-65. But 20 years ago we considered retiring to Portland very
> seriously, so I used the Gates to get back my original call -- W7UOX -- and
> then shorten it to W7OX.
>
> I like having the call for old times sake. But I do wish the prefixes had call
> area geographic meaning as they did in olden days.
>
> 73, Phil W7OX