Well, not really, Mike. The magnitude of the impedance at the end of a
wire can vary from low to very high [several thousand ohms] depending on
its electrical length. As David pointed out, the general Elecraft ATU
design is an L-network using relays to combine various fixed values of
inductance and capacitance. I believe my KX1 had 64 possible
combinations, the KAT2 has more, and the KAT3 has even more I think.
While the ATU may not be able to directly match extremely high or low
impedances, a simple transformer will usually get the value into a range
that can be matched. My end-fed WOOF has a transformer at the feed
point ... don't know if it's 4:1 [16:1 Z ratio], or 9:1 [81:1 Z ratio],
but the KAT3 and KAT2 both find matches in the 1.0:1 - 1.3:1 range on
all bands. It is located on the fence, about 10 ft from the shack
entrance weatherhead, but is fed through 100 ft of RG-8 right now ...
long story involving my wife. 😉 While I can get a match on 6 m and
occasionally hear signals, no one has ever answered my calls. 10 - 160
work fine.
I don't know what algorithm Elecraft uses to search for a match, it's
probably proprietary, but I'd guess its based on some variant of a
steepest descent design. Before microprocessors, some hams used an
analog ATU design, often in mobile installations. A coupler sensed both
the voltage and current in the feedline at the antenna and a phase
comparator operated a motor driving a variable capacitor in an L-network
to the zero phase difference point. Small loops often use this design
today.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 02/07/2022 23:13, Mister Mike wrote:
"The “automatic” antenna tuner is a completely new concept for me. They
appear to be designed to tune unbalanced coaxial feedlines and not an
end-fed wire."
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