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OT; Feedline question

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Richard Fjeld-2

OT; Feedline question

Forgive me for the OT, but there are many antenna people here above my
pay-grade.

I need to replace the spacers on my ladder line. If I deviate from the
standard spacer length for impedance
(separation between conductors), are there problems I'm not thinking
of? I use a quality manual tuner, and
an 80 meter delta loop.

Perhaps it would be best to reply off line for this. Thank you in advance.

Dick, n0ce

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Matt Zilmer-3

Re: OT; Feedline question

This is an amateur topic, so there's no reason to take it offline, imho.

If you run the impedance vs spacing calculations, you'll see the spacing
doesn't make a whale of a lot of difference. I don't have the numbers
here, but I switched from 1/2 of a BIC pen body (hole centers about 2"
apart) to some ceramic spacers another ham gave me a box full of. The
new spacers had centers about 3.2" apart. I had to re-tune the ATU on
most bands, but everything continued to work fine. From (a tired old)
memory, the impedance varied from about 450 ohms to something like 600
ohms, but let someone on a computer run the calcs for this. It just
didn't make enough difference to worry about, but did change the ladder
feed's impedance.

This antenna is a doublet about 180' long at 45 feet height, fed with
the ladder line (61' of it, from memory). The ladder line terminates
into a 1:1 balun (Elecraft BL2) and the last 20 feet is LMR400 low-loss
coax back to the station's antenna switch. It continues to work just as
well as with the earlier ladder spacers.

73,

matt W6NIA

On 04/15/2017 09:39 AM, Richard Fjeld wrote:

> Forgive me for the OT, but there are many antenna people here above my
> pay-grade.
>
> I need to replace the spacers on my ladder line. If I deviate from the
> standard spacer length for impedance
> (separation between conductors), are there problems I'm not thinking
> of? I use a quality manual tuner, and
> an 80 meter delta loop.
>
> Perhaps it would be best to reply off line for this. Thank you in advance.
>
> Dick, n0ce
>

--
"Always store beer in a dark place." -- R. Heinlein

Matt Zilmer, W6NIA
[Voignier]

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Lynn W. Taylor, WB6UUT-2

Re: OT; Feedline question

Off-list one person learns. On-list we all learn.

On 4/15/2017 10:16 AM, Matt Zilmer wrote:
> This is an amateur topic, so there's no reason to take it offline, imho.
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Matt Zilmer-3

Re: OT; Feedline question

Very true!

Got back in front of my desktop 'puter and made an Excel worksheet to
calculate the characteristic impedance at various spacings and wire
sizes. The real variable is the ratio of spacing divided by wire
diameter (only the ratio matters). Everything else in the formula is a
constant for our purposes.

16 AWG, 1 inchspacing: Zc = 436 ohms

16 AWG, 2 inchspacing: Zc= 519 ohms

16 AWG, 3 inch spacing: Zc= 567 ohms

18 AWG, 1 inch sp: Zc = 464 ohms

18 AWG, 2 inch sp: Zc = 547 ohms

18 AWG, 3 inch sp: Zc = 595 ohms

Or for you QRO ops: 3/0 AWG, 9 inch spacing: Zc = 450 ohms. 3/0
(three-aught) is quite hefty, being 0.4" in diameter. Probably overkill
for the average Joe Ham.

The commercial ladder line I use is 18 AWG with about 0.9" spacing (hard
to measure), giving 451 ohms. I think there is a lot of this type in use.

Anyway, for the wire sizes and spacings we would normally use, the Zc is
nearly the same value, which is all I was saying before.

The formulas for all this are pretty well documented at
http://hamwaves.com/zc.circular/en/index.html.

73,

matt W6NIA

On 4/15/2017 10:52 AM, Lynn W. Taylor, WB6UUT wrote:

> Off-list one person learns. On-list we all learn.
>
> On 4/15/2017 10:16 AM, Matt Zilmer wrote:
>> This is an amateur topic, so there's no reason to take it offline, imho.
> ______________________________________________________________
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-- unknonwn

Matt Zilmer, W6NIA
[Shiraz]

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Clay Autery

Re: OT; Feedline question

Thanks....

So, these numbers are for BARE copper, right?
Using insulated wire changes things a bunch....

For instance 18 GA THHN/THWN has an approx. dc of 2.35, XLPE has a dc of
5 or so.... As the dielectric constant gets larger, things get real....
fast.

18 GA THHN/THWN... (dc = 2.35 approx.)

To get the same 464 Ohms, the Center to center distance must increase to
7.52 inches or so...
The impedance with the quoted 1, 2, and 3 inch "D":

1" = 305-306 Ohms

2" = 359-360 Ohms

3" = 391-392 Ohms

I use 300 Ohm, 18 GA copper twin-lead with foam over wires and some hard
plastic over that.... It's close to true 300 Ohm...

I'll have to go calculate the min size safe against various power
levels... The separation distances get big fast with increase in the
conductor diameter, too.

73,

PS - there is an argument to be made for NOT using bare wire.... if
anything MIGHT touch the feedline... and wet wire.... wet wire
changes performance a lot... built with insulated wire, the changes are
MUCH smaller with wet wire...

______________________
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389

On 4/15/2017 4:56 PM, Matt Zilmer wrote:

> Very true!
>
> Got back in front of my desktop 'puter and made an Excel worksheet to
> calculate the characteristic impedance at various spacings and wire
> sizes. The real variable is the ratio of spacing divided by wire
> diameter (only the ratio matters). Everything else in the formula is a
> constant for our purposes.
>
> 16 AWG, 1 inchspacing: Zc = 436 ohms
>
> 16 AWG, 2 inchspacing: Zc= 519 ohms
>
> 16 AWG, 3 inch spacing: Zc= 567 ohms
>
> 18 AWG, 1 inch sp: Zc = 464 ohms
>
> 18 AWG, 2 inch sp: Zc = 547 ohms
>
> 18 AWG, 3 inch sp: Zc = 595 ohms
>
> Or for you QRO ops: 3/0 AWG, 9 inch spacing: Zc = 450 ohms. 3/0
> (three-aught) is quite hefty, being 0.4" in diameter. Probably
> overkill for the average Joe Ham.
>
> The commercial ladder line I use is 18 AWG with about 0.9" spacing
> (hard to measure), giving 451 ohms. I think there is a lot of this
> type in use.
>
> Anyway, for the wire sizes and spacings we would normally use, the Zc
> is nearly the same value, which is all I was saying before.
>
> The formulas for all this are pretty well documented at
> http://hamwaves.com/zc.circular/en/index.html.
>
> 73,
>
> matt W6NIA

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Richard Fjeld-2

Re: OT; Feedline question

In reply to this post by Richard Fjeld-2

Okay, and thanks to all for the info which I will save.

What made me curious is that twin lead is stated in steps of 150 ohms.
IE. 300, 450, 600.
I assumed it was to match the impedance of certain antennas such as a
folded dipole, etc.
Since I understand my loop to be a non-resonant antenna, and using a
manual tuner, I thought
I'd be okay to change the spacer dims, but I wondered if I was
over-looking something.

Thanks again,

Dick, n0ce

On 4/15/2017 11:39 AM, Richard Fjeld wrote:

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Matt Zilmer-3

Re: OT; Feedline question

In reply to this post by Clay Autery

I was trying to find the dielectric constant (Epsilon sub r) for this
poly jacket that's used on the standard HRO-available line. The
calculations I did were for open wire line with air being the dialectric
(something like 1.0054). The first ladder line that I used was made
from BIC pens, cut in half for about 3" center to center. After that
much hassle to put together and raise, when it got wind-blown and torn
up, I just started using the HRO stuff.

Have only seen really heavy feeds in use at SW BC stations, and only
twice at that. Looked like 4 AWG, but might've been heavier. Some of
WWVH's curtain feeds lookmuch the same.

73,

matt W6NIA

On 4/15/2017 3:56 PM, Clay Autery wrote:

> Thanks....
>
> So, these numbers are for BARE copper, right?
> Using insulated wire changes things a bunch....
>
> For instance 18 GA THHN/THWN has an approx. dc of 2.35, XLPE has a dc of
> 5 or so.... As the dielectric constant gets larger, things get real....
> fast.
>
> 18 GA THHN/THWN... (dc = 2.35 approx.)
>
> To get the same 464 Ohms, the Center to center distance must increase to
> 7.52 inches or so...
> The impedance with the quoted 1, 2, and 3 inch "D":
>
> 1" = 305-306 Ohms
>
> 2" = 359-360 Ohms
>
> 3" = 391-392 Ohms
>
> I use 300 Ohm, 18 GA copper twin-lead with foam over wires and some hard
> plastic over that.... It's close to true 300 Ohm...
>
> I'll have to go calculate the min size safe against various power
> levels... The separation distances get big fast with increase in the
> conductor diameter, too.
>
> 73,
>
> PS - there is an argument to be made for NOT using bare wire.... if
> anything MIGHT touch the feedline... and wet wire.... wet wire
> changes performance a lot... built with insulated wire, the changes are
> MUCH smaller with wet wire...
>
> ______________________
> Clay Autery, KY5G
> MONTAC Enterprises
> (318) 518-1389
>
> On 4/15/2017 4:56 PM, Matt Zilmer wrote:
>> Very true!
>>
>> Got back in front of my desktop 'puter and made an Excel worksheet to
>> calculate the characteristic impedance at various spacings and wire
>> sizes. The real variable is the ratio of spacing divided by wire
>> diameter (only the ratio matters). Everything else in the formula is a
>> constant for our purposes.
>>
>> 16 AWG, 1 inchspacing: Zc = 436 ohms
>>
>> 16 AWG, 2 inchspacing: Zc= 519 ohms
>>
>> 16 AWG, 3 inch spacing: Zc= 567 ohms
>>
>> 18 AWG, 1 inch sp: Zc = 464 ohms
>>
>> 18 AWG, 2 inch sp: Zc = 547 ohms
>>
>> 18 AWG, 3 inch sp: Zc = 595 ohms
>>
>> Or for you QRO ops: 3/0 AWG, 9 inch spacing: Zc = 450 ohms. 3/0
>> (three-aught) is quite hefty, being 0.4" in diameter. Probably
>> overkill for the average Joe Ham.
>>
>> The commercial ladder line I use is 18 AWG with about 0.9" spacing
>> (hard to measure), giving 451 ohms. I think there is a lot of this
>> type in use.
>>
>> Anyway, for the wire sizes and spacings we would normally use, the Zc
>> is nearly the same value, which is all I was saying before.
>>
>> The formulas for all this are pretty well documented at
>> http://hamwaves.com/zc.circular/en/index.html.
>>
>> 73,
>>
>> matt W6NIA
> ______________________________________________________________
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>
> This list hosted by: http://www.qsl.net
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> Message delivered to [hidden email]

Matt Zilmer-3

Re: OT; Feedline question

In reply to this post by Richard Fjeld-2

I don't think you're missing anything. It was a good question. Please
also see Clay's reply.

73,

matt W6NIA

On 4/15/2017 4:08 PM, Richard Fjeld wrote:

> Okay, and thanks to all for the info which I will save.
>
> What made me curious is that twin lead is stated in steps of 150 ohms.
> IE. 300, 450, 600.
> I assumed it was to match the impedance of certain antennas such as a
> folded dipole, etc.
> Since I understand my loop to be a non-resonant antenna, and using a
> manual tuner, I thought
> I'd be okay to change the spacer dims, but I wondered if I was
> over-looking something.
>
> Thanks again,
>
> Dick, n0ce
>
>
>
> On 4/15/2017 11:39 AM, Richard Fjeld wrote:
>> Forgive me for the OT, but there are many antenna people here above my
>> pay-grade.
>>
>> I need to replace the spacers on my ladder line. If I deviate from the
>> standard spacer length for impedance
>> (separation between conductors), are there problems I'm not thinking
>> of? I use a quality manual tuner, and
>> an 80 meter delta loop.
>>
>> Perhaps it would be best to reply off line for this. Thank you in advance.
>>
>> Dick, n0ce
>>

Wes Stewart-2

Re: OT; Feedline question

In reply to this post by Clay Autery

Why do you suppose a little bit of dielectric on the wire would make a huge
change, when the majority of dielectric is still air?

On 4/15/2017 3:56 PM, Clay Autery wrote:

Clay Autery

Re: OT; Feedline question

Actually thermoplastics are NOT majority air.... I'm not an expert
here, but the dielectric constant appears to increase with thickness and
probably with density of the material.

Keep in mind that the standard insulation on THHN is 0.015"
thermoplastic (PVC) and that is covered by a 3-4 mill layer of clear
nylon to protect the insulation on conduit pulls...

I've given up trying to understand it all fully....

I've just decided to treat the entire feedline assembly from tuner
(radio) to antenna as a impedance matching network....
Bottom line.... getting the impedances in band to such a level that you
can tune it...

______________________
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389

On 4/15/2017 8:02 PM, Wes Stewart wrote:

> Why do you suppose a little bit of dielectric on the wire would make a
> huge change, when the majority of dielectric is still air?
>
>
> On 4/15/2017 3:56 PM, Clay Autery wrote:
>> Thanks....
>>
>> So, these numbers are for BARE copper, right?
>> Using insulated wire changes things a bunch....
>>
>> For instance 18 GA THHN/THWN has an approx. dc of 2.35, XLPE has a dc of
>> 5 or so.... As the dielectric constant gets larger, things get real....
>> fast.
>>
>> 18 GA THHN/THWN... (dc = 2.35 approx.)
>>
>> To get the same 464 Ohms, the Center to center distance must increase to
>> 7.52 inches or so...
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
> 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]

Wes Stewart-2

Re: OT; Feedline question

I'll agree with both points.

That said, think about the space between wires. On and about the wires is a
relatively thin layer of plastic. From there, the space between wires is filled
with...wait for it...air.

It might be worthwhile to read this: http://k6mhe.com/n7ws/Ladder_Line.pdf

On 4/15/2017 6:16 PM, Clay Autery wrote:
> Actually thermoplastics are NOT majority air.... I'm not an expert
> here,

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alorona

Re: OT; Feedline question

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
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Clay Autery

Re: OT; Feedline question

And your effort is most sincerely appreciated. :)

______________________
Clay Autery, KY5G

On 4/17/2017 10:31 PM, Al Lorona wrote:
> 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.

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