Paul,
I have been using an 80m drop wire, I call it, for years off my 160m
vertical.
My irrigation pipe vertical is 72ft with 4 - 30ft top hat wires for 160m.
The 80m wire is installed and insulated on the 160m vertical at abt 65ft
and spaced just 16 inches.
The key to make the 80m wire/vertical to work is that the 160m must be
grounded. I use a large relay to permanently ground the 160m, irrigation
pipe section at the base, then remotely activate the relay to un-ground it
for 160m use. The 80m drop wire does not seem to affect 160m.
I use two feed lines and two inductors, one for each band to adjust the
resonance and SWR. Of course, a large radial field of about 100 radials
does help.
Ray,
N6VR/W7YA
On Sat, Jan 1, 2022, 3:52 AM N1BUG <paul@n1bug.com> wrote:
> I have received a large number of responses both on and off list. Thanks
> everyone!
>
> Several mentioned adding an 80m wire vertical alongside the 160m shunt
> fed tower, series feeding the 80m and using the existing radials. That
> idea has much appeal as a space and work saver if it can be made to
> work. I tried it several years ago and it didn't go well. The MFJ
> antenna analyzer said R was 1 or 2 ohms and I got nowhere trying to
> match it. I suspected it wouldn't radiate well if I did get it matched
> and gave up. I don't know why it did that, but it can only be
> interaction with the grounded tower. The antenna configuration has since
> changed on that tower so I will try that again.
>
> I've considered adding another shunt feed to the tower for 80m but am
> not sure it is worth the effort. At one point I did have the single
> shunt feed on that tower working on both 160 and 80. It was weird in
> that all I had to do was switch out some fixed capacitors for 80! Pure
> luck. It worked great on 160 but was a poor DX antenna on 80. The tower
> was electrically just a bit under a half wavelength on 80 at the time. I
> would have to check but I suspect it is now electrically more than a
> half wavelength.
>
> One or more half wave slopers off one of my existing towers was
> mentioned several times. I don't rule that out entirely but I am trying
> very hard to avoid more wires and anchor points. I have so many already
> and I am trying to save some space in case I want to put a VHF or UHF
> EME array in somewhere in the future. I'm on a mission to eliminate wire
> antennas and additional guyed structures partly for that reason.
>
> As far as my original idea, I really cannot imagine 30' of Rohn 25 with
> a 35' stinger on top falling over or being damaged by our weather. As
> far as my concern about bolt hole elongation, worst case if it turns out
> to be a problem I suppose I could weld the leg joints!? If I go this
> route I have no intention of hinging the base but I would provide a
> means of attaching temporary guys when I needed to climb it.
>
> I'm still thinking and looking over some of the many ideas in response
> to this.
>
> My basic problem is I am always stretching the limits of space and
> budget to the breaking point. I understand only too well overcrowding of
> antennas becomes a performance issue. I just strive to get things to
> work as well as I can with what I have.
>
> Happy New Year to all
>
> Paul N1BUG
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