(Richard Harrison) wrote:
Floyd Davidson wrote:
"Richard you can cut the bull**** out."

Floyd claims to have measured microwave paths for 40 years. I`ve been
doing it since 1960, so that`s about as long.

I`ve made repeated measurements over a number of years on the same
repeaters. During normal propagation, which is by far most of the time,
path loss like other system losses is very constant.

Of course there are periods of anomalous propagation. It depends on
location, season, and time of day. It`s worse when the atmosphere is
stagnant.

So now you say it's constant except for when it's not! Your designs
are within 1 dB except when they aren't.

I *am* impressed.

I`m sure that marginal paths with insufficient clearance and other
problems may have propagation which comes and goes. I`ve seen some, but
I haven`t built any like that.

That's why I asked if you'd built many.

In fact it is quit common, and most paths have anomalies. Most of
course aren't very interesting. But others are. Suggesting your
designs have never collided with such an anomaly just means you
either didn't really do many or you're failing to recall them.

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd Davidson wrote:
"Suggesting your designs have never collided with such an anomaly just
means you didn`t do many or you`re failing to recall them."

It means care was taken in path planning. Microwave propagation is very
predictable. The only variable is the atmosphere and long statistical
records are available which allow a design for a percent reliability,
99.99 out to the limit of your budget.

Of course, on any particular path, there will be fades on some foggy
morning, but that doesn`t guarantee failure if you`ve planned for it.
The phone company uses alternate routing. I`ve designed similar systems.

What I said was, the as-built hops performed as designed during normal
propagation. That`s nearly all of the time. The received carrier power
measures remarkably close to the predicted value nearly every time and
if it doesn`t when the the alignment is complete, in my experience, it
has been always due to a defect in the system, not in its design..

I have never had to go back and "beef up" a hop to obtain reliability,
and I`ve put some hops in tough territory. The arithmetic is simple and
so are the criteria.

Best regards, Richard Harrison, KB5WZI

Floyd Davidson wrote:
"This thing (TV microwave relay station) was located 50 miles from town
at 8500 foot up on a mountain top. They had a 50 foot tower (at the TV
studios I suppose)----they turned it on and it worked great."

So, if it wasn`t broke, why did they fix it?

Floyd also wrote:
"But somebody had the smart idea to see what happens if they slide the
dish down the tower to see if the signal would improve. It did!."

I wasn`t there, so I can only speculate, but I might have not been
surprised by those results.

On a 50-mile path with plenty of mid-path clearance, propagation is
similar to communications with a satellite. One difference at the
Arizona latitude is the vertical angle the dish path makes with the
Earth. The low angle the dish on the terrestrial path makes with the
Earth, makes it vulnerable to reflections from the Earth. The higher the
dish is placed, the more vulnerable it becomes. That`s a reason to go
high / low on a reflective path, and not high/high. (Low/low won`t make
the trip on most long paths due to Earth curvature).

Best regards, Richard Harrison, KB5WZI

(Richard Harrison) wrote:
Floyd Davidson wrote:
"This thing (TV microwave relay station) was located 50 miles from town
at 8500 foot up on a mountain top. They had a 50 foot tower (at the TV
studios I suppose)----they turned it on and it worked great."

So, if it wasn`t broke, why did they fix it?

Floyd also wrote:
"But somebody had the smart idea to see what happens if they slide the
dish down the tower to see if the signal would improve. It did!."

I wasn`t there, so I can only speculate, but I might have not been
surprised by those results.

On a 50-mile path with plenty of mid-path clearance, propagation is
similar to communications with a satellite. One difference at the
Arizona latitude is the vertical angle the dish path makes with the
Earth. The low angle the dish on the terrestrial path makes with the
Earth, makes it vulnerable to reflections from the Earth. The higher the
dish is placed, the more vulnerable it becomes. That`s a reason to go
high / low on a reflective path, and not high/high. (Low/low won`t make
the trip on most long paths due to Earth curvature).

A 50 foot tower on top of an 8400' mountain. What are you
talking about high/low etc etc. I wasn't there when the
decision was made to put it on a 50 foot tower, and neither you
nor I have any idea why that was done. Perhaps the topo maps
were wrong, and some obstacle they assumed was there didn't
actually exist. Perhaps the engineer made a mistake. I don't
know and you don't know. But, you don't suppose the engineer
knew exactly what he was doing, eh???

A 40 foot change in elevation suggests there simply were no
obstacles, so one has to wonder what the 50 foot tower was
supposed to accomplish... other than allow a range of adjustment
to find the best point for signal strength. Because this was
not a 50 mile shot, it was much closer to 100 miles and no doubt
they were very interested in optimizing the signal strength.
With no obstacles, not even earth bulge, calculating reflections
isn't so easy... unless you move the antenna vertically to find
the right position.

But, it doesn't emulate "a satellite" shot even in the slightest.
Or, not for real satellite shots at least.

E.g., the look angle for a geosynchronous satellite here is only
10-12 degrees or less depending on where the satellite is. I
don't agree at all that a 50 mile microwave path with no
obstacles is approaching similarity to a satellite shot! Some
satellite links have *less* clearance.

Of course, your exposure to satellites might not be that great.

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd Davidson wrote:
"But, it doesn`t emulate "a satellite" shot in the slightest."

A satellite is a microwave repeater in the sky which is usually not
susceptible to earth reflections.

Terrestrial microwave paths are often designed to minimize earth
reflection.

Reason is, on a long path, the lengths of the direct ray and the Earth
reflected ray are almost the same. Reflection reverses the phase of the
reflected ray so that the reflected ray detracts from the direct ray
when they combine at the receiver. They arrive out-of-phase, at least at
some antenna altitudes.

The phase of the signal undergoes 180-degrees of phase change as we
examine the signal either forward or backwards from the plane of the
signal. That is to say, the phase of the signal is a function of
distance along the path. When a second signal source is created by Earth
reflection on the path, the combination of the direct and reflected rays
produces strata of stronger and weaker signal intensities as altitude
changes. No reflected signal, no significant variation of signal with
altitude, given sufficient path clearance. This is a worthwhile design
goal.

No matter which end of the TV relay path was varied to produce a
significant signal strength change, the attenuation at the higher
elevation was probably caused by an Earth reflection. Another reflecting
surface near the microwave path could have been the reflector. I`ve seen
that in the city canyons I`ve had to squeeze signals through. But on
most paths, the Earth is the most likely reflector.

Best regards, Richard Harrison, KB5WZI

Floyd Davidson wrote:
"---the look angle for a geosynchronous satellite here is about 12
degrees if the satellite is directly south."

Floyd is in Alaska. Floyd`s example of anomalous propagation from
reflection to a terrestial transmission was in Arizona. On the equator,
the "look angle" may be nearly straight up.

The reason a satellite dish is less susceptible to earth reflections is
that the satellite dish is not aimed to pick the reflections up. The
satellite dish is aimed at the sky.

A terrestrial microwave dish aimed directly at the satellite dish is
likely not transmitting an interfering frequency, but if so, it is
unlikely to be aligned well enough or above the horizon of the satellite
dish.

The approximate specifications of a 6-foot dish for beamwidth and gain
versus frequency a

1.3 GHz 9 deg. 25 dbi

2.3 GHz 5 deg. 30 dbi

3.5 GHz 4 deg. 33 dbi

6 GHz 2 deg. 36 dbi

10 GHz 1.5 deg 43 dbi

25 GHz 0.5 deg 50 dbi

Sources of the above are the "RSGB VHF-UHF Manual" and the ARRL Antenna
book (they agree).

In moderate latitudes, the satellite earth station antenna is really
looking up. It is quite likely terrestrial signals are not within range
of its bandwidth, beamwidth, or distance.

Best regards, Richard Harrison, KB5WZI

(Richard Harrison) wrote:
Floyd Davidson wrote:
"---the look angle for a geosynchronous satellite here is about 12
degrees if the satellite is directly south."

Floyd is in Alaska. Floyd`s example of anomalous propagation from
reflection to a terrestial transmission was in Arizona. On the equator,
the "look angle" may be nearly straight up.

The reason a satellite dish is less susceptible to earth reflections is
that the satellite dish is not aimed to pick the reflections up. The
satellite dish is aimed at the sky.

The reason your example is poor is that it assumes something
which *clearly* is not always true. Satellite dish antennas are
not always aimed significantly far away from the earth's
surface.

A terrestrial microwave dish aimed directly at the satellite dish is
likely not transmitting an interfering frequency, but if so, it is
unlikely to be aligned well enough or above the horizon of the satellite
dish.

That is not necessarily true. And in fact I've seen 4 gig
terrestrial microwave systems cause grievous interference to
satellite systems. (In one case, by reflections off a metal
building across the street from the satellite dish, which caused
the weird effect of the interference coming from a microwave
that was 20 miles distant directly *behind* the direction the
satellite dish was pointed!).

The approximate specifications of a 6-foot dish for beamwidth and gain
versus frequency a

This doesn't account for side lobes, and hence gives a *very* false
indication of the actual susceptibility to interference arriving at
angles off the main lobe.

1.3 GHz 9 deg. 25 dbi

2.3 GHz 5 deg. 30 dbi

3.5 GHz 4 deg. 33 dbi

6 GHz 2 deg. 36 dbi

10 GHz 1.5 deg 43 dbi

25 GHz 0.5 deg 50 dbi

Sources of the above are the "RSGB VHF-UHF Manual" and the ARRL Antenna
book (they agree).

In moderate latitudes, the satellite earth station antenna is really
looking up. It is quite likely terrestrial signals are not within range
of its bandwidth, beamwidth, or distance.

But not all microwave systems requiring path engineering are
located so convenient for your specifications. It is simply false
to claim that, even at moderate latitudes, the satellite antenna
is *necessarily* looking at a high angle above the terrain. Locations
with small latitudes *can* see some satellites at high angles, while
locations at high latitudes *never* see a geosynchronous satellite
at a high angle. But in either case there are *many* satellites
at lower angles.

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd Davidson wrote:
"And darned if a few years later a build up of rhime ice on the 43 feet
of tower above the dish didn`t fall down and bend that dish into a pile
of rubble too,"

By Floyd`s logic the lesson must be that a dish must always top the
tower, out of harms way.

The antenna does not have to receive zero interference, though that
would be nice. We are always susceptible to some interference from
somewhere at some time. Multiphop systems often must reuse just a few
frequency pairs over and over. It`s all the regulators will allow.
Situations arise when anomalous propagation provides strong signals at
extraordinary distances.

Planning includes avoiding azimuths which would repeat to present
interference at a great distance along with a repetition of a frequency
which might interfere. A solution to interference is coordination.
Another is often high performance dishes which do a better job of
rejection. I`ve used the shielded variety from Antennas For
Communications (AFC) with good success.

Ice may be falling, but the sky isn`t in the case of microwave
interference.

Best regards, Richard Harrison, KB5WZI

(Richard Harrison) wrote:
Floyd Davidson wrote:
"And darned if a few years later a build up of rhime ice on the 43 feet
of tower above the dish didn`t fall down and bend that dish into a pile
of rubble too,"

By Floyd`s logic the lesson must be that a dish must always top the
tower, out of harms way.

Richard, stop being an ass. Nothing that I've said suggested
any such stupidity, yet you frivolous and insulting.

The antenna does not have to receive zero interference, though that
would be nice. We are always susceptible to some interference from
somewhere at some time.

So you finally got my point! It *is* going to have variations,
and those variations are *not* something you will likely
calculate to with the 1 dB you claimed to do _every_ _single_
_time_.

Multiphop systems often must reuse just a few
frequency pairs over and over. It`s all the regulators will allow.
Situations arise when anomalous propagation provides strong signals at
extraordinary distances.

More frivolous commentary that has nothing to do with the topic
of discussion. What is your point?

Planning includes avoiding azimuths which would repeat to present
interference at a great distance along with a repetition of a frequency
which might interfere. A solution to interference is coordination.

Coordination is not optional. You cannot get a station license
without it.

Another is often high performance dishes which do a better job of
rejection. I`ve used the shielded variety from Antennas For
Communications (AFC) with good success.

Ice may be falling, but the sky isn`t in the case of microwave
interference.

The only sky falling is your claims that you calculate path
losses to within 1 dB for *every single* microwave shot. It
just doesn't work that way Richard, and you are either 1) not
doing many path calculations, or 2) are forgetting about the
ones had some anomolous differences causing unexpected results.

Perhaps 98% of all microwave paths work out just about as expected,
but the other 2% are really interesting and sometimes we never do
figure out exactly what is causing the difference between calculated
and actual results. Any path over tidal water comes to mind... :-)

--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd Davidson wrote:
"The only sky falling is your claim that you calculate path losses to
within 1 dB for every single microwave shot."

I wrote many boring postings ago:
"---my best received carrier power was very nearly always within a db of
my calculations."

That was very nearly, not every single microwave shot. That was during
normal propagation conditions, not during fades. It was and is a true
statement. Such results can be achieved by anyone who plans the system
correctly using the required accurate information.

Best regards, Richard Harrison, KB5WZI