It's always interesting to read patents, as it gives you insight into how a
designer perceives the customer problem to be solved..it can give insight into
the "whole" problem the designer is wrestling with.
Here's a patent by Martin Jue. (just issued in 2008)
http://www.google.com/patents?id=Y3awAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false
<http://www.google.com/patents?id=Y3awAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false>
It's not clear to me whether it's valid, as there's probably prior art.
But you can see how he goes thru the justification for adding a shunt capacitor
to the input of a T-network tuner
He's trying to deal with the problems of high power, and 160m thru 10m
operation, matching into a wide range, into one tuner.
"A wide bandwidth high-power T network tuner obtains its wide bandwidth
operation by connecting a fixed capacitor between the input and ground, with
the
tuner using large, series connected variable capacitors for high power so as to
solve the minimum capacitance problem on the higher frequencies"
Read all that, and tell me if he's going in the right or wrong direction for
his
market. Or: what he SHOULD be selling/designing.
In fact, the "differential T" tuner of MFJ actually adds another twist, right?:
simplifying operation by not giving you the ability to twist two Caps. they
move
in concert. So there is only one setting that works. (compared to a normal T
tuner)...But you lose some amount of "what you can match".
I think part of the design problem here, is that customers respond to vendors
trying to appear to "solve all problems".
Now if "problem" isn't well defined, it's easy to be wrong, and then customers
complain because they bought your marketing.
funny: i was looking in the closet, and I have a QRP tuner from MFJ that I
bought in 1976. I opened it up. Nice little assembly. fixed selection of turns
around a 3 stack of cores, and a variable cap! Vintage MFJ gear :)
-kevin
ad6z
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