On 5/31/2011 5:40 PM, John S wrote:

A folded dipole is about 300 ohms. A half-wave shorted transmission line
is about 0 ohms. So, if you take a shorted half-wave transmission line
and spread the wires apart at the 1/4W point all the way to where it
becomes a folded dipole, it seems to me that the terminal resistance
will go from zero to 300 ohms and 50 ohms is in there somewhere.

I tried it in EZNEC and found that to be the case. I found that, if the
acute angle of the rhombus is about 51.5 degrees, then the terminal
resistance is about 50 ohms (adjust perimeter along with angle to get
50+j0).

As an aside, I found it time consuming to adjust angles and repeat the
source impedance test in EZNEC. So, I created an Excel spreadsheet where
I could simply input the perimeter, the acute angle, height above
ground, wire gauges, and number of segments and wrote a short VBA to
gather the spreadsheet results and create an EZNEC importable file.

Man, what a time saver.

73,
John

On May 31, 3:46*pm, John S wrote:
On 5/31/2011 5:40 PM, John S wrote:

A folded dipole is about 300 ohms. A half-wave shorted transmission line
is about 0 ohms. So, if you take a shorted half-wave transmission line
and spread the wires apart at the 1/4W point all the way to where it
becomes a folded dipole, it seems to me that the terminal resistance
will go from zero to 300 ohms and 50 ohms is in there somewhere.

I tried it in EZNEC and found that to be the case. I found that, if the
acute angle of the rhombus is about 51.5 degrees, then the terminal
resistance is about 50 ohms (adjust perimeter along with angle to get
50+j0).

As an aside, I found it time consuming to adjust angles and repeat the
source impedance test in EZNEC. So, I created an Excel spreadsheet where
I could simply input the perimeter, the acute angle, height above
ground, wire gauges, and number of segments and wrote a short VBA to
gather the spreadsheet results and create an EZNEC importable file.

Man, what a time saver.

73,
John

That sounds like something that would be valuable to others, too,
John. You might think about making it available...

BTW, I do think pretty deeply about a lot of things, but there are far
more I don't bother with. Still, people who do think deeply about all
those other things hold my respect for what they do, whether it's
topics I have any interest in or not. Along with that is an
understanding of how important it is that we can freely share what we
learn with others.

Cheers,
Tom

On 5/31/2011 11:59 PM, K7ITM wrote:
On May 31, 3:46 pm, John wrote:
On 5/31/2011 5:40 PM, John S wrote:
As an aside, I found it time consuming to adjust angles and repeat the
source impedance test in EZNEC. So, I created an Excel spreadsheet where
I could simply input the perimeter, the acute angle, height above
ground, wire gauges, and number of segments and wrote a short VBA to
gather the spreadsheet results and create an EZNEC importable file.

Man, what a time saver.

73,
John

That sounds like something that would be valuable to others, too,
John. You might think about making it available...


It is so narrowly focused on the rhombus that I doubt it would be useful
to anybody else. But, it is available to anybody who wants it.

John