> -------- Original Message --------
> Subject: Topband: Upside down Vertical Antenna
> From: "Y.G.Yu" <hl5bpl@kornet.net>
> Date: Fri, November 09, 2007 1:36 am
> To: <topband@contesting.com>
>
> Recently I moved to new apartment house.
> It is 15th floor and we have void space in front of the building.
> Because the height of my room would be more than 40 meters,
> it would be possible to install a little sloped 1/4 wave length wire
> vertical antenna. To reduce the length of coaxial feed line, I am
> thinking about the "Upside down vertical antenna".
> Do anyone have experience for this kind of configuration? I have no
> idea how to install the radials.
> 73!
> Yu HL5BPL
>
>
Moxon, G6XN, is a big fan of half wave verticals. He shows numerous
designs in his book "HF Antennas For All Locations". He uses
seemingly tiny 'counterpoise' wires under quarter wave verticals,
and he resonates these short wires.
The example given by VE7BS, of a 134ft vertical wire working against
a (presumably resonant) vertical whip on a balcony railing is most
intriguing! This sounds like a pretty good approach, probably far
better than attempting any sort of 'aerial counterpoise' schemes.
Indeed, isn't the VE7BS example simply the G6XN half wave vertical
'turned on its head'? Yes, the loaded vertical whip is lossy, but
the 134ft wire probably makes up for that very well. (Just so long
as the whip loading coil can handle the transmitter power level)
It would be a good idea to use a choke coil near the feedpoint to
avoid feedline radiation- either a single layer (solenoidal) coil
of good size, or an effective ferrite choke of the sort N4IS is
playing with recently. He measured 40dB attenuation with one of his
designs, 4ea. FT50B-77 torids in binocular configuration with
8 turns of RG-316/U.
http://www.angelfire.com/md/k3ky/WF_CHOKES_N4IS_REV01.pdf
This is a 381KB pdf download.
73, David K3KY
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|