Sorry Dan,
The Comprod UHF Corner Reflector is the 440-70 or 442-70 URL:
http://www.comprodcom.com/en/antennas/base/pdf/440-70.pdf. There are several
different models for UHF that offer different gain, pattern shape (beam width)
and front to back ratios. You should be able to find a model that fits your
application. Same rules apply about getting the other antenna nearby oriented
behind yours.
Bill
----- Original Message -----
From: Dan Hancock
To: repeater builders
Sent: Saturday, November 21, 2009 8:47 AM
Subject: [Repeater-Builder] Re: Antenna Pattern Question
Bill, thanks for the tip, however the repeater is a UHF. I don't see
anything on Comprod's site showing a UHF with a reflector screen.
I guess I will just have to improvise! I was looking to see if any
other members had done such a thing before so I didn't have to re-invent the
wheel so to speak.
73,
Dan N8DJP
Re: Antenna Pattern Question
Posted by: "William Becks" [email protected] wgbecks
Date: Fri Nov 20, 2009 7:18 pm ((PST))
Dan,
The VHF fiberglass Omni's within 6 feet of your building-top antenna
can cause pattern distortion just as is the case with side mounted tower
installations. However, I recall from your original posting that your
application requirement is to produce a deep null +/- 45 degrees with as much
gain as possible elsewhere around the compass. The best candidate for this
application would be a corner reflector array such as the Comprod 470-70
(Assuming VHF) that develops 30 dB Front to Back with a main horizontal beam
width of 67 degrees. Check URL:
http://www.comprodcom.com/en/antennas/base/pdf/471-70.pdf
If the 67 degree horizontal beam width is too narrow for your intended
coverage area and you can live a little less front to back ratio, then a better
choice would be the Comprod F-3713 that has a flat reflector screen mounted
behind the folded dipole radiator elements. Check URL:
http://www.comprodcom.com/en/ecatalogs/BaseStation2005-Full.pdf
You should expect to obtain nearly the same published pattern shape and
gain with either of these antennas for your building-top installation provided
that you are able to mount your antenna such that the fiberglass Omni's are
behind the reflector and not out in front of the main beam of the array. This
gives you the advantage of a large reduction in radiation (excitation) toward
the Omni's that significantly reduce overall parasitic radiation from these
sources with little or no net change from published pattern shape and gain. A
secondary benefit is an increase in isolation from the other VHF systems that
may prevent or reduce the possibility of receiver desense or transmitter IM
among the three systems sharing the rooftop.
Good luck with your project!
Bill, WA8WG
