Vic Rosenthal wrote:
>>
>> >What is the SWR as measured at the generator with a 50-ohm
>> >characteristic-Z SWR meter?
>>
>> ? At the end of an any characteristic.-Z halfwave transmission line, the
>> termination Z repeats itself -- with a reactance reversal. . Since
>> there is no reactance in this termination, the Z at the end of the 93-ohm
>> halfwave line is 50 +/- j0 ohms, the SWR is 1:1.
>
>No. It is correct that the impedance seen by the generator is 50 ohms but
>the
>SWR is unchanged, regardless of the line length. The SWR is entirely
>determined by the impedances of the line and the load.
This isn't correct, Vic.
In a 93 Ohm system, the SWR is unchanged. However, we are attempting to
measure a 50 Ohm load in a system where 50 Ohms is our base (the SWR meter has
been specified as being 50 Ohms and the exciter is also assumed to be at 50
Ohms).
At a half wavelength of coax, you rotate completely around the VSWR circle and
thus see the impedance of the load at the input of the coax. In this case, the
load is 50 Ohms. At the half wavelength of coax, the load is 50 Ohms as well.
The SWR in a 50 Ohm system then is 1:1. In a 93 Ohm system you would have the
SWR mismatch of 1.86:1, but in a 50 Ohm system, our VSWR is 1:1.
So the bottom line is that if you have a 50 Ohm load and a 1/2 wavelength of
coax that it matters not what the impedance of that coax is! It's inherently
narrow band, but that's the case.
73,
Jon
KE9NA
--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|