Re: 5.8 GHz PtP Backhaul Options

Old Dog

Ken, Dave;

Thanks for the info on that tool.  I dusted off my old Radio Mobile models this evening.

Ken that path was from my roof top (second story about 20 feet AGL)  very close to where you first placed me.  The end at the school was at about the 200 foot level. It was set up with three 5.8 GHz APs on sector antennas.  They were to be a PtMP backhaul system to serve the POPs we had in Mathews.  Below that around 120 feet we put the 900 MHz APs.  We used 900 MHz as our last mile system in that network. There was a backhaul above it that ran 5.8 between that site and White Stone.  The AP at White Stone was somewhere between 150 and 200 as that tower was only 200 feet.  I don't recall but it would not surprise me if the high end of that backhaul from White Stone was on the Mathews side at around 250 to 270 feet.    

Dave, this area is blessed with trees ;).  A rule of thumb I was taught in my misspent youth is simple enough to be done in your head and accurate enough to be useful in the field (or before computers).  Above 300 MHz you loose ~1 dB to absorption for every 100 MHz of frequency through every 100 meters of veg.  So a 900 MHz link through 1800 meters of trees which is otherwise Fresnel clean will exhibit about 9 x 18 dB of absorption.  Clearly it won't work.  A 2.4 GHz shot through 400 meters of trees is going to shed about 4 x 24 dB and again going to be pretty darn iffy.  It might run with a couple of 27 dB grid dishes at each end.   But that 900 MHz link through 400 meters of trees is going to easily make if you have a 17 dB Yagi on each end.  An interesting phenomenon is that as frequencies slip into the upper SHF there are often paths through the vegetation which are not occluded and function almost like tunnels. 

I look forward to working with you gentlemen.   I have much to learn.

On Thu, Apr 9, 2020 at 11:03 PM Dave Hewlett via <> wrote:

I’m glad to see we are starting to see some coordinating amongst areas to interconnect. That is exactly what we were aiming for when we started this group. 

I do have a point to add to your discussion concerning terrain. While it is true in theory that trees will reek havoc with your signal, in Hampton they found that in the 5gig band, if your end points are directional (i.e. dishes) the ERP will make a significant improvement, and in some cases, negate the effect of trees. 

One of the backbone links (before one end got hit by lightning) connected a hospital with the eoc. It did this through a fairly dense expanse of trees. 

The real world does not always fit the nice neat equations so the best thing to do is give it a try. 


Dave WA4OPE 

On Apr 9, 2020, at 10:34 PM, Ken Jamrogowicz via <> wrote:

If you are not familiar with the 'heywhatsthat" tool - the coverage pattern is for a receive location six feet off the ground - roughly the location of a human eyeball.  For specific locations, you put in the coords, click parameters and put in the height of the other end (AGL or ASL).

For your Matthews location, a path is indeed possible - although it has a bit of a problem - depending on the height at the other end(see attached).

The "pinch point" is actually covered by a lot of trees, so you have to clear those as well as the dirt there (second image attached).

Looking at the satellite map, I see quite a tall tower at the Matthews end, so I am guessing you are quite high on that tower and thus I would expect it to work.

I am too far north to reach down your way.  "Assets" around here tend to be tall buildings where people are employed and various places where there are already VHF/UHF repeaters (hospitals, water tanks, hotels).   I can suggest you look in a repeater directory.



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