even if the harness is balanced it's only effective at the design freq so a
freq change makes a phase shift and alters the tilt / transmission angle ?
To: Repeater-Builder@yahoogroups.com
From: [EMAIL PROTECTED]
Date: Sun, 8 Jun 2008 08:23:34 -0500
Subject: Re: [Repeater-Builder] Re: antenna suggestions for 440mhz
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 ?
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
at CarPoint.com.au It's simple! Sell your car for just $30
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