RadioBanter - View Single Post - An antenna question--43 ft vertical

[email protected] · July 8th 15, 11:07 PM posted to rec.radio.amateur.antenna

John S wrote:
On 7/8/2015 1:39 PM, wrote:
John S wrote:
On 7/7/2015 1:58 PM, wrote:
John S wrote:
On 7/5/2015 7:21 PM, wrote:
John S wrote:
On 7/5/2015 5:24 PM, wrote:
Roger Hayter wrote:
wrote:

The output impedance of an amateur transmitter IS approximately 50 Ohms
as is trivially shown by reading the specifications for the transmitter
which was designed and manufactured to match a 50 Ohm load.

Do you think all those manuals are lies?

You are starting with a false premise which makes everything after that
false.

A quick google demonstrates dozens of specification sheets that say the
transmitter is designed for a 50 ohm load, and none that mention its
output impedance.

If the source impedance were other than 50 Ohms, the SWR with 50 Ohm
coax and a 50 Ohm antenna would be high. It is not.

Where is the source impedance found on a Smith chart? Also, if you have
EZNEC, you will not find a place to specify source impedance but it will
show the SWR.

A Smith chart is normalized to 1.

EZNEC allows you to set the impedance to anything you want and assumes
the transmission line matches the transmitter.

The EZNEC help file is very comprehensive. Please find any reference to
your assertion that there is an assumption of source impedance there and
provide information for us to verify your assertion.

Why don't you email the author and get his take on your assumptions?

Why don't YOU? You are the one in need of knowledge. If I do it and
report back here you will just doubt it or find something else to argue
about. Better you should do it first-hand.

EZNEC calculates the SWR presented to the SOURCE which is usually
placed at the antenna terminals.

EZNEC also calculates the SWR presented to the SOURCE which can be
modeled as a SOURCE at one end of a transmission line and the antenna
at the other end.

SWR is defined in terms of SOURCE impedance and LOAD impedance.

No. It is defined as Vmax/Vmin on the line. Show an equation that
defines SWR as the matching of the source to the line.

OK, since you insist, one more time:

SWR = (1 + |r|)/(1 - |r|)

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php

--
Jim Pennino