Greg,
I have insomnia tonight, so I just emailed you a
plot of a 80m dipole, at your height of 78 feet,
showing the azimuth pattern for 3.530 MHz, 7.030
MHz, and 14.030 MHz. This EZnec analysis shows
what patterns you can expect for the three bands
by using just an 80m dipole. If you add 40 and
20m dipoles to your 80m dipole, you should expect
to get patterns on 40 and 20 m, similar to the
plot you get for 80m, using just your 80m dipole.
If I don't go to sleep tonight, I will add both a
40 and a 20m dipole to the 80m dipole (at the
same feed point) and see what the actual EZnec
analysis shows for the patterns, then send them to you also.
I've been a ham for over 53 years and it took me
48 of those years to finally move to open wire
feeders. (slow learner!!) I have a single 80m
dipole at 70 foot height and run 600' of four
inch spaced #14 open wire feeders, supported by
five 4"x4"x12' weather treated post, to it. I
bring the open wire into the eves of the house,
into the attic, and then down through the ceiling
into my operating room, using two foot sections
of nylon toilet water hose adapters, one for each
wire, available for $0.99 each at the local
hardware store. I use a Johnson KW Match Box
tuner at my operating table. For contesting I run
a full 1.5 KW output from my Titan 3. This
antenna works extremely well on both 80 and 40m
and shockingly well on 20m. BUT that is my
antenna at MY location...and that may not work at your location!
I personally have a very low opinion of baluns of
any type in any antenna except in it's proper
place, on a yagi. In my opinion, they are a
non-necessary expense, and additional RF loss in
both transmit and receive, and do very little in
the way of making the radiation pattern of a
dipole a purely symmetrical figure 8 radiation
pattern on it's band of intended design. Again,
my opinion, if your intent is to minimize your RF
losses, do not use a matching device that
incorporates a balun. These type 'tuners' are
designed for and work well with unbalanced coax
feed. Find a matching unit that is specifically
designed for open wire feeders, there are several
now available, even though their prices are
outrageous. If your lucky, you could find an old Johnson KW Match Box tuner.
I would suggest you start out by trying just the
80m dipole, fed with open wire feeders (the
length doesn't matter as long as you stay away
from an odd number of quarter wave lengths), and
a true matching unit specifically designed for
open wire feeders. Test it to your satisfaction
and then decide if you think you need to add the
extra dipoles to your 80m dipole. Because the
same antenna can vary so much, depending on your
location and how carefully you install it, there
is no one correct answer for you, even though you
may very well get many suggestions.
Will see if I can get some additional plots for
you, if you wish, of the 80/40/20 dipoles at the same feed point.
73,
Tommy - W4BQF
At Monday 11:45 PM 7/18/2005, you wrote:
I NEED YOUR ADVICE:
I have a Centurion Amp that I want to run on all bands 160 through 10 with a
single horizontal antenna up 78 feet with as wide a gain pattern as
possible.
My proposed solution is to use multiple dipoles cut for 80, 40, and 20
jointly fed at 78 feet high 250 feet away from the house fed with 1200 watts
via 300+ feet of open wire feed line (450 ohm). The reason I am proposing
to use three dipoles is to try to get a broader pattern (lobes) across the
bands rather than narrow lobes (but high gain) patterns off the ends of the
wires that would result in the higher bands if I just used the 80 meter
dipole. I could also run a 160 dipole in parallel if that would help. Or, I
could select different length or number of dipoles, but I really donâ??t want
to have more than wrestle with more than 2 or 3 dipoles total hooked
together at that height.
I have several verticals, but they pick up severe local noise, so thatâ??s not
a solution (my ears hurt even with a ClearSpeech?which helps a lot). I
cannot put up a tower and beam for 20 through 10 meters at this time
(wouldnâ??t you just love a set of Fluidmotion SteppIR MonstIRs stacked at 70
and 140 feet!) so for right now high dipoles is the best I can do?although
that is probably a good solution because I have been told that dipoles at
this height will roughly equal or even beat a 3 el beam at 38 feet, without
the cost and rotators, etc., due to vertical takeoff angle.
Questions:
1. Will the Ten Tec 238B handle this power if I run the open wire to
these jointly fed dipoles, even though it is not a â??balancedâ?? type tuner?
2. Would it be better or make a difference if I converted to coax just
outside the house and then use the coax position on the 238?
3. If the 238B wonâ??t handle it, is there a better solution or a better
tuner that will handle the 1200 watts that would be the same or less price
(money is a factor). I have to admit that I am biased in that Iâ??d like to
stay with Ten Tec if at all possible.
4. What would you suggest I do, trying to keep as broad a pattern on
most bands? Would a different combination of dipoles work better? Would a
160, 40, 17 meter combo work better?
I followed some of the recent discussion on the Ten Tec List on a related
topic which were very helpful in forming my current proposal, but the only
solutions I heard for high power amps like the Centurion were some higher
priced or hard to find tuners.
Please share your experience and advice with me,
Thanks & 73,
Greg, N6GK
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