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

Roger Hayter · July 8th 15, 10:23 PM posted to rec.radio.amateur.antenna

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.

I am tired of typing in the same equations over and over again.

Zo is the characteristiic impedance of the transmission line and nothing
to do with the source impedance of whatever generator is supplying power
to the system.

--
Roger Hayter