W4PV:
>I have installed 2 parallel beverages each approximately 520 ft long, spaced
421 ft apart (using available trees, etc for support). According to ON4UN's
book this spacing might not be the best. Should I try and get the spacing
down to between 350 - 375 ft and what difference would I notice with this
change?
Not much difference...certainly not worth moving
them. A quick look shows slight widening of the forwardbeam width
from 42.8 degrees to 49.6 degrees which causes
slight degradation in RDF from 13.2 to 12.6. I doubt you
would notice these differences. However I hope you have
been careful with alignment of this system since it has
fairly narrow forward beam width for Europe. I would not
point it at the nominal direction of 40 degrees, but skew
it slightly southwards, to ~55 degrees. Then your 3 dB
beam width will cover 34 degrees (Scandinavia/Central Asia)
to 76 degrees (Europe in auroral conditions and N Africa).
I find Europe often skews well southwards (70 deg) and you
might be missing this if you centered your array on 40
degrees with the southern edge of the lobe beginning to
drop off at 61 degrees.
Patrick, the question I would ask is "Where does most
of your noise come from?" If it is from the South to
Southwest, as most of mine is, I would consider an end-fire
system. This gives MUCH better F/R performance than a
parallel system, and only requires another ~120' in length
versus a single Beverage. ON4UN introduces a new metric in
his book which is called DMF (Directivity Merit Figure)
which is an integrated average of the entire rear hemisphere
of an antenna. If you look at ON4UN's tables showing DMF
(think "average F/R") for end-fire arrays, you will see that
they have much better performance for rejecting noise from
the rear.
Choice of end-fire or parallel should be determined by
where your worst noise comes from. From the East Coast, I
would normally opt for end-fire to Europe since noise comes
from Texas to Caribbean thunderstorms. If I were back in
Colorado, where I had to "look through" noise from the
Texas/Oklahoma area, I would probably choose parallel since
it better allows "slicing through" the noise ahead of me
(with my caveat above about beam width and skewing issues).
Of course if you have infinite real estate, a combination
of parallel and end-fire Beverages (4) is best!
73, Bill W4ZV
P.S. I could have made a bad assumption that your Beverage
is for Europe, but hopefully my comments still make sense.
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