> > Even if the tower and yagi combination, at the feedpoint of the
> > slopper, is not resonant the antenna can have a good SWR.
> >
> > All you do is change the length of the slopper, until the system is
> > resonant.
> >
> I didn't want to get in this discussion, but since I stupidly started
> it by mistakenly sending that C/C message to the entire list, I have
> to comment on the above statement. The conception you can simply
> change the length of wire on a 1/4 wave sloper to achieve a "good" SWR
> is simply not true.
I could have been clearer, and of course you are correct. It won't
always work.
What I tried to say is if REACTANCE at the tower connection point
is a problem, you can cancel it by changing length of the slopper
as LONG as resistance is within a reasonable match range. It does
not matter of the tower impedance is reactive as long as the
resistive part is very low, because slopper length can be tweaked
to tune out reasonable amounts of reactance.
If RESISTANCE is wrong at the final X=0 length of the sloper, you
are stuck with the resulting SWR even when you make X=0. The
critical thing is resistances, since problems can not be corrected
by slightly changing sloper length.
Of course you could use a matching transformer or stub, but let's
not go here.
My point was the tower does not need to present a X=0 for a low
SWR, not that any impedance will work.
73, Tom W8JI
W8JI@contesting.com
________________________________________________________________________
This list is sponsored by the new eHam.net Store. When you buy products
like ICE filters, Array Solutions StackMatch, or M-Squared Antennas from
the eHam Store for the same price you pay direct, a portion of the sale
price goes to support this list. Check it out at http://www.eham.net.
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|