Hi Jon.
Appreciate your time, but still having trouble...
This email ping-pong certainly isn't the most efficient way to get
technical concepts across :)
On Friday, October 01, 1999 4:40 PM, Jon Ogden [SMTP:jono@enteract.com]
wrote:
> Gilmer, Mike wrote:
>
> >If the cable/antenna were treated as a black box, with some
impedance, Z
> >(caused by the cable length's transforming effect on the antenna
> >impedance), and some VSWR (caused by the mismatch of the cable and
> >antenna), what does the "amp" see when it looks into the black box?
> >It sees, of course, the same VSWR and the same impedance.
> >So this means I can't expect a SWR meter between the amp and the
black
> >box to read 1:1 even if the black box is 50 ohms. Is this true?
>
> No, that's not true. If the black box is 50 Ohms, the output of the
PA
> is 50 Ohms, and if your SWR meter is 50 Ohms, then you see 1:1 VSWR.
I don't care about this case (yet). I talked about mismatched
cable/antenna.
The
> impedance transformation effect of the cable only really does
something
> if the impedance of the antenna is different from the impedance of the
> feedline.
This is EXACTLY the case I'm talking about. I said the antenna's
impedance was transformed by the cable. This means the Zcable does NOT
equal Zantenna. In this case, you said I could get a 50-ohm point at
some cable length. If I have this cable length, and I treat this
cable/antenna as a black box (which is what I tried to describe above)
what does my SWR meter between the amp and the blackbox read?
> If you want a further explanation of the Smith Chart, I'd love to give
> it. Unfortunately, I don't have my text book that best explains
matching
> theory with me in my office. But the Smith Chart really makes
> understanding things easy and simplifies the math incredibly. Seeing
it
> visually really helps.
>
I've used the Smith chart many times, but it's been 10 years.
Will look up the beast this weekend (if it rains!)
>
> 73,
>
> Jon
> KE9NA
Tnx
Mike N2MG
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