I should have thought a change from resonance will cause a phase shift in the
matching/harness therefore a change in tilt , or have I been reading the wrong
books ?
To: Repeater-Builder@yahoogroups.com
From: [EMAIL PROTECTED]
Date: Sun, 8 Jun 2008 07:53:23 -0500
Subject: Re: [Repeater-Builder] Re: antenna suggestions for 440mhz
Paul;
If the elements continue to be fed in-phase, the
main lobe cannot shift up or down
It may, however, become narrower or wider, causing
a gain or loss of signal at some point below the
perpendicular-to-the-plane-of-the-elements line at a distance, thus giving an
APPARENT shift up or down
Regards,
Gary
----- Original Message -----
From:
Paul Plack
To: Repeater-Builder@yahoogroups.com
Sent: Saturday, June 07, 2008 7:18
PM
Subject: Re: [Repeater-Builder] Re:
antenna suggestions for 440mhz
"No, parallel-fed antennas do NOT suffer uptilt/downtilt as
frequency is varied unless the harness was special-ordered for factory
downtilt. If the antenna wasn't ordered with downtilt, all of the elements
are
fed in phase, and they will always be in phase regardless of
frequency."
Jeff, the pattern depends on both phasing and spacing. As
frequency drops, the interelement phasing, expressed in degrees, remains the
same, but the spacing, expressed in degrees or wavelengths, drops. If you
model a colinear array of parallel-fed dipoles in an antenna
software program, and don't scale the dimensions as you scale the frequency,
you'll see the main lobe shift up or down, and "butterfly" lobes appear, as
you get a few per cent off-frequency.
In an extreme case, a pair of vertical colinear dipoles fed
in phase with half-wave spacing has the familiar big lobe toward the horizon.
As frequency rises, the pattern degrades until, at a frequency of 2X, it
becomes an end-fire array, with most energy directed straight up and down.
This happens with no change in phasing or spacing.
73,
Paul, AE4KR
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