Hello Dave,
You may be able to improve the VSWR match, but the antenna may still not
perform well. What kind of an antenna is it? If it is the typical
fiberglass collinear antenna, the internal elements will be too short.
Using a 154MHz antenna on 146.745MHz will mean that the elements will be
about 5% too short. It is my understanding that when you shorten the
elements on a collinear array by 2% you will get about a 3% down-tilt
off the horizon of the antenna angle of radiation. Your antenna (if it
is a collinear) will have quite a serious down-tilt with the 5% shorter
elements. This may not be bad on a very high site covering very low
terrain around it, or if you are trying to keep the signal from
propagating much farther from the horizon. If the terrain that you are
trying to cover is not much lower than the repeater site elevation you
may have a coverage issue.
Look At:
<www.ad4c.us/Antennas/collinearantenna.doc>
and look at his comments about down-tilt.
73, Joe, K1ike
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On 5/9/2010 12:13 AM, WA3GIN wrote:
Hi folks,
Several weeks ago I posed the question of using a Commercial VHF
antenna that was resonant on 154Mhz on 146.745Mhz. We tried it today.
The SWR was a bit over 2:1 on the repeater freq. We installed a T
connector after the cans and used an open stub to try to match the
line...got it down to 1.5:1, wouldn't go any lower.
We think the height of the antenna makes up for what we suspect is a
lot of loss in the antenna. The previous location of the repeater
antenna was 100ft ASL and this location is 525ft ASL. Maybe one day
we'll get a chance to retune the four dipole antenna.
Thanks to all that provided ideas for this project.
73,
dave
wa3gin
