Larry, your excellent results suggest that you have already solved the
"desert radial" problem!
On the unworkable 80m feed problem, that is easily solved by use of a
parallel tuned circuit from the base feed point to ground. The antenna is
connected to the hot end of the tuned circuit and the 50 ohm feed is connected
to one of the inductor turns near the bottom. The coax shield and cold end of
the tuned circuit are connected to ground of coarse.
If the feed is connected to a turn 10% up the inductor, then the
transformation is very close to 10 squared or 5000 ohms. Works just like an
auto
transformer. The C part of the tuned circuit can be a variable capacitor,
allowing resonance anywhere in the band. Part of the C can also be from the
antenna if shortened slightly. Along the same lines, part of the L can also be
from the antenna if made slightly long.
73,
Gerald K5GW
In a message dated 12/27/2012 10:58:17 A.M. Central Standard Time,
lwloen@gmail.com writes:
I had very good results on 80 with an HF2V and an extensive ground radial
system in Minnesota.
Got a lot of 80 DX, including zone 23 (supposedly the hardest for WAZ on
80). Did not get all zones, though, in a year or two over the last sunspot
minimum. Was also a fine performer on 40 and even surprisingly adequate
(with an antenna tuner) on 30 meters. Wrote it all up in the Feb 2007 CQ
magazine including my then-results on 80.
I am thinking about trying the inverted L next as well.
The real question is the radial system here on the dessert. I have heard
that the dessert soil makes a poor buried radial system, so I'm thinking of
trying tuned radials above ground. Not really sure on how to do this one.
I've also looked into the inverted L and may deploy one.
Some thoughts: The most widely seen inverted "L" design is actually for
160. This seems to be the one you're describing. You have to work on it
to get a usable 80 meter system (apparently, by changing the size of the
top loading "L" portion). If you look a the "standard" designs, 80 meters
is kind of unworkable with a huge feed point impedance.
Like many antennas on 80 (including my HF2V as well as the inverted L), the
better your radial system on the "L", the _lousier_ the SWR (or so I
read). Certainly true for the HF2V. These antennas have very non-standard
values in terms of Ohms at the feed point. So, more radials (in most of
the designs I've seen) actually puts the antenna closer to its ideal design
point. But while this increases the actual signal radiated (by up to
double) it also makes the SWR worse, so matching takes a bit more effort.
In my CQ article, I showed how you could pin the radials to the ground
rather than do all of the (literally) sod busting to bury them. Worked
very well and took way, way less time. My riding mower did pick up a few,
but most stayed pinned nicely.
I'm sure all of this discussion is in ON4UN's book. If I can solve the
dessert radial problem, I may well deploy both solutions.
One thing about the inverted "L" is that one might perform some
interesting
experiments in antenna supports. I have no trees (this is AZ), but I wonder
if I can safely get some narrow gauge steel or fiberglass in the air,
safely, guyed by dacron ropes (only dacron will stand up to the AZ sun).
Anyone know of good designs? The 160 version would require 55 to 60 foot
supports, perhaps, though I wonder if I can let the "L" sag such that I can
have the far end be more like 20 feet that I have deployed before. The 60
foot "main" line could be in parallel with my tower, then, suspended from
it.
Larry Wo0Z
On Thu, Dec 27, 2012 at 8:50 AM, Jack White <m5pro@hotmail.com> wrote:
> Hi
>
> I've been reading the ON4UN book and antenna articles online on and off
> for a couple of years now but I thought I'd share my situation with some
> more experienced Guys on here to see if I can perhaps find some new
> information and ideas.
>
> I have a modest HF/6 station that covers 40-6. I have a painted 3 section
> 60ft Versatower (suspect v. poor electrical connection between sections)
> with an Optibeam OB1-4030, Optibeam OB9-5 and 5L 6M Yagi all mounted on
a
> 15ft stub mast and fed into an Array Solutions Ratpak. (Antenna pic on
QRZ)
> The 6M Yagi has grounded elements but the Optibeam elements are insulated
> from the boom and tower. The station is working nicely now so I feel it's
> time to add an 80M DX TX antenna. I am interested in 3.5MHz CW only, so
> bandwidth/phone etc not an issue.
>
> In the past I've tried an 80M coax fed inverted vee with the apex at 60ft
> - as expected dynamite out to a couple of thousand miles but no good for
> DX. I've ruled out the possibility of shunt feeding the tower because of
> the Optibeams and the poor connection between sections. So currently I'm
> left with two ideas:
>
> MFJ-1792 or Butternut HF2V mounted 50ft from the tower (landscaped
gardens
> prevent mounting anywhere else)
>
> Inverted L hanging off the tower with approx 60ft vertical section.
>
> What I guess really matters is the tower's resonant frequency, looking at
> the details above, would anybody like to guess? Because the Optibeams are
> insulated from the tower do they still effect the tower's resonant
> frequency? If it is resonant close to 80M I guess the RF fed into a vert
> 50ft away would see it as a parasitic element?
>
> In the worst case scenario, if the tower messed with a vertical I could
> always lower it before operating on 80M but it's not ideal.
>
> Apologies for any stupid questions and Merry Christmas to you all!
>
> Jack G8DX
>
> Sent from my iPhone
> _______________________________________________
>
>
>
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