not if all matching harness branches are the same length
----- Original Message -----
From: Barry C'
To: repeater-builder@yahoogroups.com
Sent: Sunday, June 08, 2008 8:13 AM
Subject: RE: [Repeater-Builder] Re: antenna suggestions for 440mhz
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 ?
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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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