[TowerTalk] RE: Horizontal Loops
alwilliams at olywa.net
Mon Aug 16 13:14:13 EDT 2004
----- Original Message -----
From: "Merle Bone" <merlebone at charter.net>
To: <TowerTalk at contesting.com>
Sent: Monday, August 16, 2004 9:20 AM
Subject: [TowerTalk] RE: Horizontal Loops
> W8JI said:
> With narrow lobe antennas that cannot be rotated, we have to
> plan the location of nulls or lobes or play roulette. The
> signal might fall in a 20 dB hole just as likely as on a 6dB
> It certainly is true that usage of "fixed direction gain pattern
> requires some pre-planning.
6 db peak???????
My first antenna after moving to my 8 acre site was to put up a long
antenna. Using the ARRL antenna book as a guide I decided on a
525' vee beam using the curves in the book to determine the apex
angle of the vee. The apex is at 110' and the ends at about 50' and
in the direction desired and fed with ladder line.
Later, after acquiring EZNEC, I modeled the 525 vee beam (without
including the feed line) and rotated the wires to give differing apex
angles. EZNEC shows that the resulting gain pattern shows
considerable change even for small apex angle changes.
Apparently the emphasis in the ARRL antenna book was to obtain
a multi-band vee beam rather than a maximum gain vee beam
as my apex angle of about 50 degrees resulted in the antenna
being usable on several bands but not being a "barn burner".
EZNEC reported somewhat over 20 dbi gain peak on 10 meters
which is about as much added gain over a good Yagi as the
Yagi is over a dipole. This is indeed a barn burner but EZNEC
also showed the 3db gain anglewidth to be about 5 degrees
and the 30db gain anglewidth to be not much wider!
I have over 15 antenna books but none of them cover vee beams
or rhombics in much detail. I just did a google search on them
and was quite amazed that there are a lot of hits and some
provide very good explanations and even include gain patterns.
I urge anyone interested to browse for them.
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