Mike - thanks for working on this. I've been reading the mail.
I did some microwave work back in the 70's. Mostly associated
with radar systems sighting for the FAA. Back then - no computer
help! - path analysis was manual - the bible was GTE Lenkurt's
Engineering Considerations for Microwave Communication Systems - I
still have a copy.
I hope we can get something gong. I realize it will be slow to
materialize ,and will take some effort to find good sites. And
the virus doesn't help! I can't even get my boat hauled to do the
bottom because the yard won't let me in to work!
Let me know if you need any help.
On 4/10/2020 2:06 AM, Old Dog wrote:
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
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
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
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.
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.
<pinch2020-04-09 22_22_58-Greenshot image