[NLRS] 24 ghz EN04RB 2nd Attempt

[Mike - KM0T]

Hi all, Gene - N0DQS and I tried 24 ghz again to EN04RB from EN13vc here at
the rooftop tripod location.

No Joy here, but some intresting observations.

Humidity was way up in the morning, but started backing off real quick,
about 20% reduction while we were in the beacon mode both ways taking turns.

We started early in the morning, about 9:15 or so and went till past
10:00AM.
During this time, humidity levels ranged from 95 to 70% on my side, lower at
Genes location in SD.

We heard each other right away, but as time passed, it got harder and harder
to hear each other.  In fact, at the end, it was pretty much impossible,
except for a brief smattering here and there.

We both tried to peak the signals, and both tried elevation tilt up and
down, etc.  No improvement could be found as the signal seemed to have a
wide distribution, no apparent peak when pointed in the correct direction.
With signals as weak as they were, this was hard to evaluate.  However, when
he got back here and we discussed what we were experiencing, we both had
come to the same conclusions independantly.

It was better with the higher humidity in the early start of the trys.
There was a broad varience, no real peak.  Up or down tilt of a 1/2 or 1
degrees did not help at all.  I even tried more tilt, but nothing there
either.

I had done some upgrades to the dish in the last few weeks in terms of
ergonomics and pointing aids.  I am using a "digital protractor" type of
device for leveling the dish, accurate to 0.1 degrees.  I also mounted a
12x40 bushnell scope on the dish, being as careful as possible to make it in
alignment with the waveguide feed to be within a 1/2 degree or so.

I am also useing a KVH datascope, which has a monocle view finder with
digital compass readout and declination offset.  All accurate to 0.1 degrees
too,

So I pick out an object with the datascope on the correct heading, then use
the rifle scope on the dish to point at that same object.  Then I know im on
the right heading.  ( I would have mounted the KVH scope on the dish, but
metal interaction from the dish screws up the compass - so I have to do this
two step method)

Well, the signal was where it was supposed to be in terms of heading, but as
I used the rifle scope.  I noticed a metal building a 1/2 mile away and a 2
story house roof probably 1/4 to 1/2 mile after that.  With the scope, I was
able to see it clearly that they were taller than me being on my roof.  The
metal building is about 30 feet tall as well.

I got to talking to Gene about this and my conclusion is that our path is
obstructed by these items.    The metal building is at the same elevation as
my house, but on the roof Im only 22 feet or so.  So it would appear that
most of the signal is being reflected or absorbed by this metal building.

Then as I said, a quarter mile father away, is a two story house.  Its roof
is clearly above mine, as my house is only single story and the house
elevation grade is 10' above mine.  Any signal left over from passing the
metal building is probably absorbed by the shingles of the 2 story house.

So, the fact that we even heard each other I think is very important in this
reguard.  It must be "scattering" of signals that are making their way back
and forth.

Gene had a great analogy...stick your finger in front of a garden hose.  It
will spash and deflect the main amount of water, but you would still get a
bit of mist and splatter directly behind the finger.  No apparent direction
and strenght of this splashing.  Not predictable.  (I personally dont know
if this works for RF, but it sure made sense and sounded good!)

So, I think this may be what can be attributed to the broad width, no
apparent peak, the varience in the strenght and in-consistancey of the
signal.  This is how the signals appeared a few weeks ago when we tried it,
but I did not pick up on this until I looked thru the rifle scope.

I think if I can get my dish up high enough, then this path will not be an
issue.  We are going to try some paths to the east, which are same distance,
worse terrain, but no up close obstructions.  If we try at the same humidity
levels, I think it will be a good test.  Heck, we are talking about only 25
miles more than what we did before.

I am seriously thinking of making my main tower - 902 Mhz and up
only....could be lots of work!

Comments welcomed.

73

Mike - KM0T