You are here

Home » Forums » General discussion

Sector Antenna Vertical Beamwidth

3 posts / 0 new
Log in or register to post comments
Last post
Thu, 09/26/2024 - 13:27
#1
K7EOK
Sector Antenna Vertical Beamwidth
I'm trying to figure out practical meaning of the vertical beamwidth on a sector antenna.  I want to understand the vertical zone that is useable.
 
Lets say I'm putting a sector with no down tilt electric or otherwise, having a 4 deg vertical beamwidth on a tower.  If I make a triangle where the acute angle is 4 deg, the long side (adjacent) is 5000 feet (about 1 mile distance from the antenna) and then that means tan4=x/5000 where x is the usable vertical distance (contained in the 4 degree vertical width) at 5000 foot distance?  That makes about a 350 foot beam spread vertical at 5000 feet usable.  So ... if the tower has the antenna 350 feet above AGL with no downtilt, then I can start using that sector well once I'm 5000 feet away?  If I want the sector to be usable closer to that tower then I have to calculate the down tilt for the bottom edge of the vertical beam width to get the location within the usable X distance?
 
Is this the general idea how to calculate?  I don't want to aim the centerline of the vertical beamwidth to be aimed right at my other node if it's at ground level, as half the rf will go into the ground ... right?

Just want the basic yes or no to the concept.  Useable vertical beam width varies with distance from the sector ... so several miles away elevation changes beome less relevant.  Correct?  Not interested in obstructions and fine details of the frenel zone ... just basic is it possible or not possible.
 
Ed
Top
Thu, 09/26/2024 - 17:43
K6CCC
K6CCC's picture
First thing to remember is
First thing to remember is that the signal does not go from massive to gone as soon as the vertical beam pattern is exceeded.  The beamwidth pattern is a curve and we assign some rating of the beamwidth being at the point where the signal has dropped some amount from peak.  That may be 3 dB, it may be 30 dB, it likely will be something in between. The other part you did not consider is for the station that is close, the path loss is low enough that the off axis simply does not matter.  As an example, I have a Mikrotik LHG-5HPnD here in my office (just the driven element - no dish) pointed straight up.  It is talking to a Ubiquiti Rocket M5 that is pointed over 100 degrees off axis to the LHG.  But it's only a 30 foot path.  Works fine.

So yes, I believe your math is correct, but it's a trade off.  You also don't really want half your RF wasted going above everything else.  In real simple terms, if the vertical beamwidth is 4 degrees, it would not hurt to put in a degree or two of downtilt to reduce RF going over everybodies heads.
 
Top
Thu, 09/26/2024 - 21:02
K7EOK
Thanks for the thoughtful
Thanks for the thoughtful response.  I wanted to make sure my rough estimates were in the ballpark, and absolutely clear that "lobes" and various intracacies in the pattern can affect quality.  The actual site I'm preparing to use has some potential connections 10 miles away at the same elevation, and users that would try to connect from a half mile away 700-900 feet lower.  So I'm going to analyze what downtilt on each node is my best bet and hope it works the first time!

Ed
 
Top

Theme by Danetsoft and Danang Probo Sayekti inspired by Maksimer