Another advantage to switching L networks is that it's fast. In a contest
you don't want to wait for an antenna to adjust. Array Solutions used to
sell a unit similar to what N4ZR described for a 70' freestanding vertical.
John KK9A
Subject: Re: [TowerTalk] Was "43ft Vertical Feeding
From: jimlux
Date: Mon, 24 Nov 2008 06:33:05 -0800
Pete Smith wrote:
> What am I missing here. You need to cover 8 bands - surely a set of
> switched L networks, including several for band segments on 160, 80 and
> 40,
> could be built for much less than any automatic tuner capable of handling
> the power. You're not looking for continuous coverage 1.8-30 MHz, after
> all.
>
> 73, Pete N4ZR
A couple years ago I ran through a design exercise on just this
approach, and it turns out that it's about the same, either way. The
typical L network autotuner has 7 or 8 L's (and their relays) and 7 or 8
C's (and their relays) (the SGC with a pi network has more C's, total).
Now consider 8 L networks.. 8 Ls, 8 Cs, 8 relays (if you use DPDTs) or
16 relays (if you use SPST).
So it's almost the same parts cost (the cost of the microcontroller is
negligible compared to big Ls, Cs, and relays)
There IS an advantage to the switched tuning networks, rather than the
generic L/C tuner.. you *might* be able to get lower overall loss by
optimizing the network for a specific antenna, etc. With the generic
tuner, there are some Zs that won't be efficiently matched. It's pretty
installation dependent, though.
Jim
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