[Karlnet] Re: Sector Antennas

[Blair Davis <blair@wmwisp.net>]

> 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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