He already has the feedpoint Z. "Measuring the SWR and R/X at the base of the
antenna with my Rig Experts AA-55 Zoom,"
If he removes the loading inductance and trims the wire for -j25 (and the R
stays around 30) then a shunt inductor of 5.3 uH will give a near perfect match
at 1820 kHs.
Wes N7WS
On 12/19/2021 12:50 PM, Jim Brown wrote:
On 12/19/2021 10:55 AM, Jeff Blaine wrote:
For 160 something around 8+ turns & type-31 are the "right" rule of thumb
answers.
Based on my research, a lot more turns. http://k9yc.com/2018Cookbook.pdf
Pete has received lots of good advice in this thread. I'll add this. Base
loading is a bad thing, because it places inductance at the point in the
antenna that carries the most current, and should be doing the radiating.
Better to remember that SWR is NOT a measure of antenna performance, that as
Jeff has noted, feedline loss is pretty low on 160M, and that what matters for
moderate values of SWR most is whether you amp can put power into it with the
help of a tuner. And if practical, I'd replace that length of RG8X with
something the size of RG8. OTOH, doubling the number of radials, realizing
that length of on-ground radials is not critical, would probably help TX
signal more than replacing that coax, and would change the feedpoint Z a bit.
While adding horizontal length is technically a great idea, sometimes that
isn't practical. I like Jeff's suggestion of an L-network at the feedpoint,
but the design requires either a lot of cut and try, or a sweep of the
feedpoint Z with a good vector analyzer whose data can be ported to design
software like SimSmith. I'll bet that Pete has neighbors who can do that. And
if Pete can send me a suitable sweep, I'd be happy to do a design.
73, Jim K9YC
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