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KB2VXA > TECH 27.11.03 05:14l 58 Lines 2725 Bytes #999 (0) @ WW
BID : 16032_WT3V
Read: DB0FHN GUEST OE7FMI
Subj: Re: ZL1UIC > J-Pole TNX
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<VE2PAK<N1UAN<WB1CHU<K1UGM<
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Sent: 031126/2132 16032@WT3V.#CNJ.NJ.USA.NOAM $:16032_WT3V
From: KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
To : TECH@WW
Hi Allen and readers,
From what you quoted you were given sound advice, but in your last an
important point overlooked before has come to light. You mentioned a
repeater in a high location, I would assume something like a mountain top
or broadcast tower, maybe a thousand feet or so. Then I have seen such
towers on mountain tops really adding to the importance of horizontal
radiation angle.
In such cases a dipole type of antenna would waste half of it's ERP into
the sky which is fairly unimportant at lower elevation unless extreme
range is intended. As with high elevation which by it's very nature gives
extreme range angle is all important for saturation and coverage is even
more important, you don't want signal shooting overhead, you want it to
hug the ground.
That's where colinear antennas come into play with their extremely low
radiation angles. They are called "gain" antennas for this reason
although like any omnidirectional antenna they exhibit no true gain. Such
an antenna is a must at high altitude or much of the signal would not
only be wasted into the sky but would pass over receiving antennas within
a circle, the diameter of which depends on height above average terrain
vs. horizontal radiation angle. This is well known to FM and TV broadcast
engineers and is all important for providing saturation and coverage of
the broadcast contour. One must provide satisfactory reception free from
multipath distortion in local as well as outlying areas.
Now before I get away from Amateur repeaters entirely, let me say that we
can borrow a trick from commercial and emergency service communications
engineers to get a signal into close in areas as well as providing
extended range. Especially in extremly high locations, they choose a
colinear antenna and mount it upside down. This not only gives a "flat"
pattern extending to the radio horizon but takes advantage of the minor
vertical lobes that would otherwise fly off into space and direct them
downward near the base of the tower. This technique provides uniform
saturation and coverage to the service area with a minimum of dead spots.
I hope this additional information will be found useful to remember even
if you don't use it for your particular application. It's just another
way to work the ground wave since burying the antenna won't work on VHF.
(;->)
73 de Warren, KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
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Message timed by cesium laser: 21:40 on 2003-Nov-26 GMT
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