On Monday, October 04, 1999 12:25 PM, Jon Ogden [SMTP:jono@enteract.com]
wrote:
> 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.
> >>
> >
What I was trying to describe, and I believe Pete understood it be, was
the case of having some arbitrary fixed load impedance and changing
frequency (tuning around) to look for a dip in VSWR. Pete said that the
minimum would occur at zero reactance.
> >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.
> >
>
What's your point? The center IS zero reactive.
Also, minimum SWR, in some arbitrary cable/load system, may not be at
the center.
> 73,
>
> Jon
> KE9NA
>
73
Mike
N2MG
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