On 11/23/2014 11:17 AM, Wayne wrote:


"John S" wrote in message ...

I like antennas that are short-circuited DC-wise. Mainly because, at
one time I had a radio on a vertical and lightning struck about a mile
away and blocked my receiver for several seconds. Of course, not all
radios have a floating input, but, it impressed me.

So, I "invented" the folded unipole which would match to a 50 ohm feed.

Any interest?

Yes.

By the way, Wayne, my interests in antennas have recently been in the
70cm band (specifically 434MHz) where there are numerous cheap modules
to play with. They have only 1 or so mW output and are illegal in the US
for unlicensed operation except under strict limitations. However, with
a license, I can do what I wish as long as I comply with the
regulations. My software always sends my call letters at each
transmission, for example.

As for the folded unipole, first imagine a normal unipole. Remember that
the feed resistance is about 30 or so ohms, yes? So, the recommendation
is to droop the radials to about -45 degrees. This raises the feed
resistance to about 50 ohms.

Now, the folded unipole has a higher feed resistance than we want.
Hmmmm.. what if we RAISE the radials to compensate? Yeah, stupid, right?

It works, and I have a model here which exhibits SWR so low I cannot
measure it except with a vector voltmeter.

I am not recommending this for the average amateur because tuning the
antenna is a bit troublesome for many. It is a bit easier to adjust a
normal unipole's length than a folded unipole's length. That's why I
haven't pushed it.