Gilmer, Mike wrote:
>[SMTP:n4zr@contesting.com] wrote:
>> >You can tune around for minimum swr, but that doesn't guarantee you
>are
>> >at resonance.
>>
>> I think that the indicated SWR minimum will always correspond to zero
>> reactance.
No, that's not correct necessarily. A 100 Ohm termination used in a 50
Ohm system has no reactive components. Adding a 1/8 wavelength of 50 Ohm
transmission line will make that 100 Ohm real load look purely reactive.
Adding an additional 1/8 wavelength will make the impedance look like 25
Ohms pure resistive. One more 1/8 wavelength will make it look purely
inductive. And so on.
The SWR stayed constant in all cases at 2:1 regardless of the fact of
whether or not the load looked purely reactive or purely resistive.
>>
>
>Hmm. Me thinks you are right.
>For a given resistive part, adding any reactive component takes you
>outside the SWR circle for the resistive part alone (SWR goes up).
This is correct. For a purely resistive load, adding additional
reactance will do this. However, if you are not purely resisitive,
adding a particular reactance can improve your VSWR.
>Therefore, SWR minimum occurs at the zero reactive point.
You can't necessarily draw that conclusion. In a 50 Ohm system
(normalized Smith chart) SWR minimum is at the center.
>
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
|