Is it a folded monopole? A 50 inch vertical section fed at the base
looks to me (using EZNEC+) like it would have a native source impedance
around 3.5 ohms, which a folded monopole with equal diameter elements
would transform to 14 ohms (4:1). If that's what you are doing, you can
simply do a similar thing but with four elements to give you a 16:1
transformation. I'm pretty sure that would be more efficient than any
kind of ferrite transformer.
There is about 300 ohms of capacitive reactance involved as well. How
are you tuning that out? I presume a coil.
73,
Dave AB7E
On 5/21/2022 7:02 PM, Larry Banks via TowerTalk wrote:
Hi All,
I am designing a rather unique 10m FM vertical for my local repeater
net. It has to fit into my attic, which is only 50" tall. I have
this antenna designed, and it "should" work, but it has an impedance
of essentially 14 ohms. (Typical for a shortened antenna.) I want to
fabricate a 4:1 transformer to facilitate this. There are many such
things available on the web, many of which I question. PLUS, I wish to
design and build this myself.
I would appreciate any suggestions about how I should go about this.
Ferrite type and size, etc. I have to admit that I have not yet done
an exhaustive search of the already available sources, especially all
of the great stuff from Jim, K9YC. What I have already looked at is
lots of ads for questionable stuff.
73 -- Larry -- W1DYJ
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