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[Karlnet] Re: Sector Antennas

To: karlnet@WISPNotes.com
Subject: [Karlnet] Re: Sector Antennas
From: Blair Davis <blair@wmwisp.net>
Reply-to: blair@wmwisp.net,Karlnet Mailing List <karlnet@WISPNotes.com>
Date: Fri, 16 Jul 2004 03:44:44 -0400
List-post: <mailto:karlnet@WISPNotes.com>


I currently have 2 16db H-pol sectors each with 100 deg beamwidth.

I have a splitter and have carefully made the cables from the splitter
to the sectors exactly the same length.

I placed the sectors at the exact same height and at an angle centerline
to centerline of 100 deg with a separation of about 5inch.

It seems to work, but I have some odd gaps in the coverage. There seems
to be a null about 10-15 deg wide in the middle of the 200 deg span.... Also, the outer ends of the span have quite low gain.


any ideas? Anyone done this before?


Of course you're going to have nulls! All over the place too, not just the center. That's a whacky setup you've got there... What are you trying
to accomplish?


What I am trying to do is get 180-200 deg of coverage with H-pol. The
location is at a lake shore and I do not wish to waste power by radiating toward the water.

I have a similar setup using V-pol 120 deg sectors at another location that works just fine.

--


The simple soloution is to use 1 radio per antenna. You can't expect to split a TX signal to 2 antennas and not get nulls everywhere. Think about throwing 2 stones into a pond, the waves created by each stone are going to interact creating peaks & troughs (constructive & destructive interference points), now extend this idea into 3 dimensions and hopefully, you'll realize what you're doing wrong.


Antenna arrays have been used in radio/ microwave for decades to increase gain, to narrow beam width or to change the radiation coverage pattern. I just seem to have overlooked something in this particular setup.


I have several V-pol arrays that work great. Coverage as designed, gain is as expected and no weird nulls.

This is, however, my first H-pol array and nothing is working as expected.

BTW, When I asked if anyone had done this before, I meant on H-pol. Several years ago, it was very common for WISP's to use 2 or 3 V-pol sectors in an array on a mast or tower to get more down tilt while still getting 360deg coverage.

Blair Davis
West Michigan Wireless
269-686-8648

A Division of
Camp Communication Services, INC




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