[NLRS] 24 ghz EN04RB 2nd Attempt

[Mike - KM0T]

Curt, thanks for the note.  You will find numorous references to water vapor
path loss for frequencies above 10 to 12 GHZ.  In the ARRL UHF/Microwave
handbook is where I found most.  Im sure the ARRL handbooks touch on it as
well.  As far as how much attenuation is at 10 ghz, I have yet to find it
significant in terms of making of contact there.  In fact, for 10 ghz, rain
and fog seems to be a good thing.

AS a reminder to all, the rain scatter season is quickly approaching!

73

Mike - KM0T

----- Original Message ----- 
From: "Curt Peterson" <RCPeterson@mmmpcc.org>
To: "Mike - KM0T" <scsueepe@mtcnet.net>
Sent: Monday, March 22, 2004 2:18 PM
Subject: Re: [NLRS] 24 ghz EN04RB 2nd Attempt


> Hi Mike - I am extremely new to this high frequency propagation stuff.
What
> data are there that shows relative humidity to be significant ??  Curt
> Peterson KC0FQZ
>
> ----- Original Message -----
> From: "Mike - KM0T" <scsueepe@mtcnet.net>
> To: "Northern Lights Radio Society" <nlrs@mailman.qth.net>
> Sent: Monday, March 22, 2004 12:44 PM
> Subject: [NLRS] 24 ghz EN04RB 2nd Attempt
>
>
> > 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
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
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