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Old July 11th 03, 08:35 PM
 
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Default lining up microwave antenna's

Maybe somebody can shed some light on the following matter:

Recently I have installed an 18 GHz Microwave link, consisting of NEC-
Pasolink gear and Andrews Microwave Dishes.
Because it was a first for me, I had thought over the process of lining
up the dishes. I had heard of and read about the side-lobe vs the main-
lobe.
So I figured out the my coworker on the other end of the link should move
his dish and I would tell him the reading on my voltmeter. The higher the
better and at the peak reading he would fix the dish. Then I would do the
same on my end. And then his end a second time and then my end a second
time
We would repeat this procedure for the vertical line-up as well.
I had calculated an expected attenuation which could be converted in a
voltage reading.

Assume the reading should say 3,5 V. Well I never got anything better
than 2.8 / 2.9 volt.

COnsequently I asked NEC for advice and they said that 'you should line
up you own end using the voltmeter, and not the opposite end'. With this
advice we repeated everything and reached the expected reading of 3.5
volt. The 2.8 volt was a sidelobe of the antenna-beam

What I don't understand is that when I rotate my dish (either
horizontally or vertically) I can go from sidelobe to mainlobe to
sidelobe. I don't move the dish further left or right, I only rotate it
around a vertical or horizontal axis. When I would move the dish further
left or right or up or down, than I can visualize going from lobe to
lobe. Not by rotating the dish
That is why I used the opposite end to move the beam.

Anybody can explain where I go wrong

Regards, Ad
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Old July 11th 03, 09:00 PM
Richard Clark
 
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On Fri, 11 Jul 2003 21:35:16 +0200, wrote:

Anybody can explain where I go wrong

Regards, Ad


Hi Ad,

Looks like cross-polarization issue. As you rotate, they come into
conflict (the polarizations) and then re-emerge from conflict.
Actually, it sounds fairly bullet proof with what you got (plenty of
signal, the system probably doesn't need more than a volt, as you
would measure it).

73's
Richard Clark, KB7QHC
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Old July 13th 03, 02:52 AM
Gary Schafer
 
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Default

On Fri, 11 Jul 2003 21:35:16 +0200, wrote:

Maybe somebody can shed some light on the following matter:

Recently I have installed an 18 GHz Microwave link, consisting of NEC-
Pasolink gear and Andrews Microwave Dishes.
Because it was a first for me, I had thought over the process of lining
up the dishes. I had heard of and read about the side-lobe vs the main-
lobe.
So I figured out the my coworker on the other end of the link should move
his dish and I would tell him the reading on my voltmeter. The higher the
better and at the peak reading he would fix the dish. Then I would do the
same on my end. And then his end a second time and then my end a second
time
We would repeat this procedure for the vertical line-up as well.
I had calculated an expected attenuation which could be converted in a
voltage reading.

Assume the reading should say 3,5 V. Well I never got anything better
than 2.8 / 2.9 volt.

COnsequently I asked NEC for advice and they said that 'you should line
up you own end using the voltmeter, and not the opposite end'. With this
advice we repeated everything and reached the expected reading of 3.5
volt. The 2.8 volt was a sidelobe of the antenna-beam

What I don't understand is that when I rotate my dish (either
horizontally or vertically) I can go from sidelobe to mainlobe to
sidelobe. I don't move the dish further left or right, I only rotate it
around a vertical or horizontal axis. When I would move the dish further
left or right or up or down, than I can visualize going from lobe to
lobe. Not by rotating the dish
That is why I used the opposite end to move the beam.

Anybody can explain where I go wrong

Regards, Ad


When aligning the antennas you must swing each all the way left and
all the way right to where you are well past the beam width and any
lobes. Of course you note the signal strength as you do this. That is
the only way to be sure that you are not on a side lobe. Just moving
it a little each side of a peak or even moving it until you loose the
signal is not sufficient. You could hit a null between the main and a
side lobe and think that you have gone far enough but you still could
peak on a side lobe.
By swinging way past the lobes, each way, and noting the signal
strength as you go will assure that you find the main lobe.
Do the same in the vertical plane also.

73
Gary K4FMX

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Old July 13th 03, 06:02 AM
Richard Harrison
 
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Gary, K4FMK wrote:
"Do the same in the vertical plane also."

Never had a minor lobe identification problem.

Never improved over the bubble-level set of vertical elevation angle on
long paths either, but I always tried.

I had always calculated my path gains and losses, and my best received
carrier power was very nearly always within a db of my calculations. If
not, I had a problem. Fortunately, that was very rare.

Best regards, Richard Harrison, KB5WZI

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Old July 13th 03, 11:21 AM
Floyd Davidson
 
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(Richard Harrison) wrote:
Gary, K4FMK wrote:
"Do the same in the vertical plane also."

Never had a minor lobe identification problem.

Never improved over the bubble-level set of vertical elevation angle on
long paths either, but I always tried.

I had always calculated my path gains and losses, and my best received
carrier power was very nearly always within a db of my calculations. If
not, I had a problem. Fortunately, that was very rare.

Best regards, Richard Harrison, KB5WZI


Did you actually do very many?

The reason I ask is that there are other factors, and you
*can't* calculate them, and in some cases you can't even
adjust for them.

The best example that I know of was a TV microwave repeater that
was put in north of Tucson for a link between Tucson and Phoenix
back in the 1960's. This thing was located 50 miles from town,
at 8500 foot on a mountain top. They had a 50 foot tower
installed on a concrete base that cost $50,000 (think about that
in today's money!). And when all was said and done, they turned
it on, and it worked great!

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!

So they positioned it vertically on the tower for best signal
strength. About 7 feet off the ground... :-)

(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 ruble too.)

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



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Old July 13th 03, 01:59 PM
Richard Harrison
 
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Floyd Davidson wrote:
"Did you actually do very many?"

I`ve done single-hops, several-hop systems, and transcontinental
systems. I`ve done them on-shore, off-shore, and in a multi-hop loop
system on-shore and off-shore. I`ve done several systems with paths
sandwiched between tall buildings. I`ve done 960 radio, 2-GHz, and 6-GHz
systems. I`ve done space-diversity systems, hot-standby, and unprotected
systems. I`ve done solid-state systems, vacuum-tube systems, etc., etc.

I have no reason to say anything which is untrue. Floyd knows of an
anomalous hop in the desert. The path suffers reflections, else it would
not have great variation of signal with height. I know of many anomalous
systems, but I never built one. All of mine worked as designed.

Best regards, Richard Harrison, KB5WZI

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Old July 13th 03, 04:40 PM
Floyd Davidson
 
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(Richard Harrison) wrote:
Floyd Davidson wrote:
"Did you actually do very many?"

I`ve done single-hops, several-hop systems, and transcontinental
systems. I`ve done them on-shore, off-shore, and in a multi-hop loop
system on-shore and off-shore. I`ve done several systems with paths
sandwiched between tall buildings. I`ve done 960 radio, 2-GHz, and 6-GHz
systems. I`ve done space-diversity systems, hot-standby, and unprotected
systems. I`ve done solid-state systems, vacuum-tube systems, etc., etc.

I have no reason to say anything which is untrue. Floyd knows of an
anomalous hop in the desert. The path suffers reflections, else it would
not have great variation of signal with height. I know of many anomalous
systems, but I never built one. All of mine worked as designed.


As I pointed out, that was the most _interesting_ example that I
know of.

However, you've just stated something that I can't quite get my
arms around. "All of mine worked as designed." is stated as if
the "anomalous systems" that have a path which "suffers
reflections" are somehow not common, or not well designed, or
not normal.

Yet you mentioned "on shore" and "off shore" each twice above,
and I'm having a real difficult time thinking you've ever
designed a microwave shot across tidal waters without having
"reflections" which could not specifically be calculated. And
there is simply no way that it "worked as designed" unless you
mean you just allowed for a large enough fudge factor to account
for signal swings from day to day. The original claim that they
*all* came in within 1 dB is just hilarious.

My bet is that you have hung around and do know how these paths
function over time, and I'll bet you just exaggerated a little,
that's all.

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

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Old July 13th 03, 07:12 PM
Richard Harrison
 
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Floyd Davidson wrote:
"---I`ll bet you just exagerated a little, that`s all."

Too many hours of daylight on Floyd are taking their toll.

Everything you work with is known. precisely, including path attenuation
under normal propagation conditions. Normally, you don`t have a path
grazing at a highly reflective point. Your path survey discloses path
detractions and you adjust for the possibility of distructive
interference. You may opt for a high / low antenna placement for the
path ends, diversity, more clearance, shorter paths, and brute-force
fade margins. The high / low option lets you move the reflection point
and the reflection. Long microwave systems must have huge fade margins
anyway due to noise buildup from individual path contributions. A
receiver not too much below the overload signal point is a very quiet
receiver and contributes almost no noise to a system.

When the path design is right, the as-built numbers are almost exactly
as calculated, whether you believe it or not.

Best regards, Richard Harrison, KB5WZI

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Old July 13th 03, 08:38 PM
Floyd Davidson
 
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(Richard Harrison) wrote:
Floyd Davidson wrote:
"---I`ll bet you just exagerated a little, that`s all."

Too many hours of daylight on Floyd are taking their toll.


Look like you need some daylight.

Everything you work with is known. precisely, including path attenuation
under normal propagation conditions. Normally, you don`t have a path
grazing at a highly reflective point. Your path survey discloses path
detractions and you adjust for the possibility of distructive
interference. You may opt for a high / low antenna placement for the
path ends, diversity, more clearance, shorter paths, and brute-force
fade margins. The high / low option lets you move the reflection point
and the reflection. Long microwave systems must have huge fade margins
anyway due to noise buildup from individual path contributions. A
receiver not too much below the overload signal point is a very quiet
receiver and contributes almost no noise to a system.

When the path design is right, the as-built numbers are almost exactly
as calculated, whether you believe it or not.


Lets see, now you are saying that you go out and *measure* the
path, rather than calculate it.

And of course you measure it, *every* *single* *time*, on a day
when you *know* whether it is giving you the best path, the
worst path, or some specific point in between.

Richard you can cut the bull**** out. I've been measuring
microwave paths for 40 years. You don't calculate them to
within 1 dB. You might find out what that is after measuring it
on a regular basis for a year. (I've done *continous* path
measurements of several paths for over a year, and on two for
10 years.)

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

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Old July 13th 03, 09:49 PM
Richard Harrison
 
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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.

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.

Best regards, Richard Harrison, KB5WZI

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