NanoVNA V2 / Forum

Note: this page is a mirror of https://groups.io/g/NanoVNAV2.
Click here to join and see most recent posts.

450-OHM WINDOW LINE........OR IS IT?


David Eckhardt 2021/02/25 22:58

I was doing some modeling using SimSmith and measured values of the shack
end of my 450-foot long doublet fed with (mostly) 450-ohm window line.

I was not getting what I would expect, so I measured the Zc of a 7.17-foot
length of (claimed) 450-ohm window line. Measured values of total L and C
follow:

8.2 MHz 34.8 pF 3.51 µH Calc Zc: 318 ohms 4.85 pF / Ft
2.6 MHz 32.4 pF 3.07 µH Calc Zc: 308 ohms 4.5 pF / Ft

Measured wire center-to-center spacing is 0.85-inches
Wire is stranded AWG #16 stranded copper weld
Using an εr of 0.91, the physical parameters indicate Zc more like 430 to
440 ohms
using the calculator at: https://hamwaves.com/zc.circular/en/

So, what I have isn't 450 ohms as claimed.

REQUEST: If others have a length of this standard window line, could you
please make measurements and confirm or deny my measurement that indicate a
Zc more like 310 ohms instead of the claimed 450-ohms?
--
*Dave - WØLEV*
*Just Let Darwin Work*

Jim Lux 2021/02/25 15:24

On 2/25/21 2:58 PM, David Eckhardt wrote:
> I was doing some modeling using SimSmith and measured values of the
> shack end of my 450-foot long doublet fed with (mostly) 450-ohm window
> line.
>
> I was not getting what I would expect, so I measured the Zc of a
> 7.17-foot length of (claimed) 450-ohm window line.  Measured values of
> total L and C follow:
>
>      8.2 MHz     34.8 pF 3.51 µH     Calc Zc:  318 ohms     4.85 pF / Ft
>      2.6 MHz     32.4 pF 3.07 µH     Calc Zc:  308 ohms     4.5 pF / Ft
>
> Measured wire center-to-center spacing is 0.85-inches
> Wire is stranded AWG #16 stranded copper weld
> Using an εr of 0.91, the physical parameters indicate Zc more like 430
> to 440 ohms
>        using the calculator at: https://hamwaves.com/zc.circular/en/
> <https://hamwaves.com/zc.circular/en/>
>
It is quite a feat to get a relative epsilon less than 1 <grin> You can
do it with ionized plasmas, but I suspect that's not what you have.

I'd guess window line, which is 90% "open space" would have an er of
around 1.2 or 1.3

Does that make your numbers come out closer?



I'm a little suspicious of that calculator - AWG 16 needs to be an inch
apart for 450 ohms with er=1


Using this one:

https://www.mantaro.com/resources/impedance-calculator.htm

51 mil diameter (AWG 16), 850 mil spacing, er=1.1 -> 400 ohms

.22 pF/inch -> 2.64 pF/ft




David Eckhardt 2021/02/26 00:13

Yes, much better calculator. Yes, I biffed it a bit on εr. Wireman gives
Vp = 0.91. I measure 0.87 which yields an εr of 1.07.

But given my measurements of L and C for 7.17 feet, I still see more like
Zc = 310 ohms, not 450.

Dave - WØLEV

On Thu, Feb 25, 2021 at 11:24 PM Lux, Jim <jim@luxfamily.com> wrote:

> On 2/25/21 2:58 PM, David Eckhardt wrote:
> > I was doing some modeling using SimSmith and measured values of the
> > shack end of my 450-foot long doublet fed with (mostly) 450-ohm window
> > line.
> >
> > I was not getting what I would expect, so I measured the Zc of a
> > 7.17-foot length of (claimed) 450-ohm window line. Measured values of
> > total L and C follow:
> >
> > 8.2 MHz 34.8 pF 3.51 µH Calc Zc: 318 ohms 4.85 pF / Ft
> > 2.6 MHz 32.4 pF 3.07 µH Calc Zc: 308 ohms 4.5 pF / Ft
> >
> > Measured wire center-to-center spacing is 0.85-inches
> > Wire is stranded AWG #16 stranded copper weld
> > Using an εr of 0.91, the physical parameters indicate Zc more like 430
> > to 440 ohms
> > using the calculator at: https://hamwaves.com/zc.circular/en/
> > <https://hamwaves.com/zc.circular/en/>
> >
> It is quite a feat to get a relative epsilon less than 1 <grin> You can
> do it with ionized plasmas, but I suspect that's not what you have.
>
> I'd guess window line, which is 90% "open space" would have an er of
> around 1.2 or 1.3
>
> Does that make your numbers come out closer?
>
>
>
> I'm a little suspicious of that calculator - AWG 16 needs to be an inch
> apart for 450 ohms with er=1
>
>
> Using this one:
>
> https://www.mantaro.com/resources/impedance-calculator.htm
>
> 51 mil diameter (AWG 16), 850 mil spacing, er=1.1 -> 400 ohms
>
> .22 pF/inch -> 2.64 pF/ft
>
>
>
>
>
> > So, what I have isn't 450 ohms as claimed.
> >
> > REQUEST: If others have a length of this standard window line, could
> > you please make measurements and confirm or deny my measurement that
> > indicate a Zc more like 310 ohms instead of the claimed 450-ohms?
> > --
> > *Dave - WØLEV*
> > /*Just Let Darwin Work*/
> >
> >
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

David Eckhardt 2021/02/26 00:17

Yes, it is, Jim. We're not dealing with metamaterials!! Too many things
going on in my 74 YO gray matter. With a measured Vp of 0.87, the
effective εr should be 1.07.

Dave - WLEV

On Thu, Feb 25, 2021 at 11:24 PM Lux, Jim <jim@luxfamily.com> wrote:

> On 2/25/21 2:58 PM, David Eckhardt wrote:
> > I was doing some modeling using SimSmith and measured values of the
> > shack end of my 450-foot long doublet fed with (mostly) 450-ohm window
> > line.
> >
> > I was not getting what I would expect, so I measured the Zc of a
> > 7.17-foot length of (claimed) 450-ohm window line. Measured values of
> > total L and C follow:
> >
> > 8.2 MHz 34.8 pF 3.51 µH Calc Zc: 318 ohms 4.85 pF / Ft
> > 2.6 MHz 32.4 pF 3.07 µH Calc Zc: 308 ohms 4.5 pF / Ft
> >
> > Measured wire center-to-center spacing is 0.85-inches
> > Wire is stranded AWG #16 stranded copper weld
> > Using an εr of 0.91, the physical parameters indicate Zc more like 430
> > to 440 ohms
> > using the calculator at: https://hamwaves.com/zc.circular/en/
> > <https://hamwaves.com/zc.circular/en/>
> >
> It is quite a feat to get a relative epsilon less than 1 <grin> You can
> do it with ionized plasmas, but I suspect that's not what you have.
>
> I'd guess window line, which is 90% "open space" would have an er of
> around 1.2 or 1.3
>
> Does that make your numbers come out closer?
>
>
>
> I'm a little suspicious of that calculator - AWG 16 needs to be an inch
> apart for 450 ohms with er=1
>
>
> Using this one:
>
> https://www.mantaro.com/resources/impedance-calculator.htm
>
> 51 mil diameter (AWG 16), 850 mil spacing, er=1.1 -> 400 ohms
>
> .22 pF/inch -> 2.64 pF/ft
>
>
>
>
>
> > So, what I have isn't 450 ohms as claimed.
> >
> > REQUEST: If others have a length of this standard window line, could
> > you please make measurements and confirm or deny my measurement that
> > indicate a Zc more like 310 ohms instead of the claimed 450-ohms?
> > --
> > *Dave - WØLEV*
> > /*Just Let Darwin Work*/
> >
> >
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

Glenn Elmore 2021/02/26 06:22

High Impedance lines become difficult, actually impossible, to measure with a conventional VNA. This is because at high impedance the TM mode becomes significant and finally dominant compared to the TEM mode so that the assumption that all e-fields are orthogonal to the direction of energy flow is no longer sufficiently accurate.  A balanced line in a low relative permittivity medium such as air and having large spacing/diameter ratio approaches two independent surface wave transmission lines.  Please see the most recent RSGB Radcom+ or a draft of the same article ( http://www.sonic.net/~n6gn/ ) as the top entry on my website for further details.

Glenn n6gn

To reply to this topic, join https://groups.io/g/NanoVNAV2

View this thread on groups.io