Re: Sleeve dipoles

On a sunny day (Sat, 21 Dec 2024 21:50:58 +0000) it happened
liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in
<1r4xqqh.qpknh71bcv5n8N%liz@poppyrecords.invalid.invalid>:

....
That's more like a conventional dipole with the centre feed point
'cold'.  In the design I had in mind, the co-ax ran up inside the lower
tube of the dipole, which was earthed at the bottom.   The dipole got
progressively 'hotter' as you went up.    The feed point in the middle
was 'half-hot', so the quarter wavelength of cable feeding it acted as
an isolator and there was no difference in potential between the tube
and the braid.

I tried this some years agao:
 https://panteltje.nl/pub/AIS_161_MHz_slimjim_DIY_antenna.jpg

Note that dipoles are directional, same when mounted vertical,
so if east-west is maximum then you have a north south minimum
(I think ).

If you google 'slim_jim' you find many sites and projects, for example:
 https://km1ndy.com/build-2m-roll-up-slim-jim-antenna-crimp-pl259-uhf-connector/

For 2 meters I would prefer omnidirectional,
a quaterwave rod would closely match 50 Ohms?

For directonal use some cheap ebay yagi..

I have several for higher frequencies, including an old TV bowty thing..
 https://www.ebay.com/itm/275515127347

google 'DIY bowtie antenna' for how to make one...
 https://www.instructables.com/Indoor-Outdoor-Bowtie-Antenna/

As to grounding  bottom end of a slim_jim, even on a pole, I think
that is a bad idea... and if your transmitter is grounded it is even e RF short.

But then I am no antitenna expert, so for what it is worth.