开云体育

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 ?H Calc Zc: 318 ohms 4.85 pF / Ft
2.6 MHz 32.4 pF 3.07 ?H 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:
<>

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:



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 - W?LEV*
/*Just Let Darwin Work*/

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 ?H Calc Zc: 318 ohms 4.85 pF / Ft
2.6 MHz 32.4 pF 3.07 ?H 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:
<>

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:



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 - W?LEV*
/*Just Let Darwin Work*/