[TowerTalk] Beam Suggestions
jimlux at earthlink.net
Fri Aug 18 20:49:30 EDT 2006
At 05:20 PM 8/18/2006, k8jdc at sbcglobal.net wrote:
> That was my error to omit any references to my goals. Without writing
>a novel, I will make a few notes:
>- As I've developed my station over the last 4 years, I've tried to built a
>quality station and I'd like an antenna to help complete that. I'm not
>looking for world-class performance, but I'd like to be able to put out a
>good signal on the upper bands without apologizing for my crummy dipole.
I realize this is the *tower*talk list and not the amps list, but the 10 dB
improvement in signal strength you'll get from an amp (assuming you're
barefoot now) into your existing dipole is probably cheaper and easier than
a tower and antenna. (albeit getting a whole host of other problems like
RFI and safety issues, and completely neglecting the "other" advantages of
Comparing apples to apples (new amp vs new antenna, and used vs used same),
from a Tx standpoint, particularly on the low bands, where antenna gain is
hard to come by, the Dollars/dB definitely favors the amp (until you get to
1500W, obviously). A 3 el Steppir is good for about 5-7dB over a dipole at
the same height (according to their brochure).
Nobody is going to make you get a building permit or ask the HOA for
permission to use the amp (well, if you're serious about QRO, you might
need a permit for that 3 kW AC service to the shack). In terms of the
overall hassle factor and aesthetics, the amp tends to win.
There's a reason why the military/emcomm folks, who take a very systems
view of things, often use a multi kW amp into a lossy broadband antenna..
it works, it's easy, there's no finesse required.
In the ham world, of course, not only is there a power limit, but there's
also an appreciation for finesse, part of which is sort of view that
efficiency is important. I have to say that I haven't seen many people
supporting my contention that there should be a "wall plug power
consumption" limit for amateur radio, as opposed to some arbitrary RF power
limit at some arbitrary reference plane. The wall plug limit would start
getting people thinking about efficiency in a "real" sense.. no more 25%
efficient amplifiers fed by 40% efficient linear power supplies.
>- Considering our current propagation situation, my primary band will be
>20m. I would rank the other bands in order of desirability as 17m, 15m,
>12m, and 10m. I'm okay with the 17m/12m performance being roughly
>equivalent to a rotatable dipole as it's better than what I have now.
Performance in terms of Tx EIRP? or in terms of F/B or narrowness of
A big advantage of a beam (unless you're already running full power) is
that it's directive on receive: you can reduce the received noise from
The other sort of interesting advantage is that if you commit to the effort
of putting up a beam on a tower, you'll probably gain a lot just from
increased height. A lot of folks go from a wire at 20 ft to a beam at 60
ft. The beam gets you 5-6 dB over the dipole (maybe a bit more because of
ground loading effects on the low dipole), but the increased height can
have a huge impact (both directions: Tx and Rx). Since most people don't
do comparisons of dipole at 20ft to beam at 20ft to dipole at 60ft to beam
at 60ft, it's hard to separate the two effects out.
As Jim pointed out, you can do an awful lot with wires and cleverness.
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