>>Shoot, put it up and measure it for goodness sake!
>>Better still, ask someone who's already got one up to
>>measure his!
>
> It would be somewhat challenging to model (although an
> interesting
> problem for a class).. Most filters don't present a very
> good match
> outside their passband, reflecting almost all the power
> (but who's to
> say what phase it will have?). Likewise a stub used to
> notch a
> frequency will look like a short, reflecting all the
> power. But,
> that's connected by a (lossy) transmission line to the
> antenna, which
> will transform the reflection to something else.
The problem is every system is very different. The feedline
length and type and even the equipment affects what you can
get away with.
Stubs are not perfect shorts or perfect opens at resonance
(the opens are like in the low thousand ohms range and the
shorts like a few ohms) and they certainly don't look that
way when not resonant. The rigs don't look like 50 ohms and
the cables and filters are all misterminated, sometimes by a
large amount. The antenna doesn't deliver maximum power into
50 ohms when it is excited on a band other than the design
band, and every radio takes a different amount or receive
port power to blow up.
What works for one person in one setup won't work for
another, so there are two real solutions:
*Someone designs for worse case and every does that, causing
most people to overbuild.
*We all cut and try, saving money but spending time and
maybe if we aren't careful blowing out a receiver or
creating spurious signals once in while.
73 Tom
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