(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 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)