Beware of cheap underperforming clones

As of 2022 there are many badly performing clones on the market. V2/3GHz NanoVNA uses parts like ADF4350 and AD8342 which are costly and clones have been cutting costs by using salvaged or reject parts.

See official store and look for V2 Plus4/V2 Plus4 Pro versions only to avoid getting a bad clone. We have stopped selling V2.2 versions since October 2020, so all V2 hardware that are not Plus or Plus4 are not made by us and we can not guarantee performance.

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