The total distance between the transmitting and receiving antenna of a
microwave link at 10GHz, is 30 Km. the height of the Tx antenna is
above ground level is 20 m. the maximum acceptable total path loss is
169 dB. Furthermore there is hill located 10 km away from the
transmitter antenna with a height of 80m.

calculate the height of the receiver antenna for the path loss to be
just equal to the maximum acceptable value?

1. Antenna essentially operates in free space with no near field ground
losses because the wavelength is extremely small (3.3cm) compared to 20m
antenna height at the transmitter.

2. The effect of the 80m hill 10Km away is negligible. The arc tan is only
.008 degrees, thus the transmitter hardly "sees" it.

3. The path loss seen by an atenna at 0 feet is then 131.8 dB (Path Loss =
20log(4*pi*d/lambda)), which is much less than the desired 169dB maximum.

Answer: 0 Feet.

Definitely NOT 0 feet.

Even without the hill in the way the curvature of the earth means that the
radio horizon is at about 20km with the tx on a 20m mast. 0.6 Fresnel
clearance occurs at about 6km. and the path loss exceeds 180dB.!!
The Rx mast needs to be at about 25m to obtain a 0.6 fresnel zone clearance,
WITHOUT a hill.This would give about 150dB path loss.

Adding the 80m hill at 10km gives a single knife edge diffraction, that
increases the path loss enormously to about 200dB!!

This path loss does not change significantly until the Rx antenna height
gets so large that near line of sight is achieved. That is over 100m!! To
obtain the 169dB required figure the mast height would have to be about
250m!!!!!!!

Regards
Jeff

hello
Jeff
i am very thank full to your help, i have got Rx height 101.2

Regards
naqvi

wrote in message
oups.com...
hello
Jeff
i am very thank full to your help, i have got Rx height 101.2

Regards
naqvi

Who is right, you or Jeff? You are more than 100% off from each other.

In truth, i could receive that signal holding a hand held 10GHz receiver
while sitting on the ground. The 80m hill is nothing from an observer 10KM
away...only .006 degree from the top of the transmitter tower. It is part of
the horizon. I love it when you guys talk like you are sol knowledgeable yet
lack the common sense to conceptualize the problem as it really exists.

" In truth, i could receive that signal holding a hand held 10GHz receiver
while sitting on the ground. The 80m hill is nothing from an observer 10KM
away...only .006 degree from the top of the transmitter tower. It is part
of the horizon. I love it when you guys talk like you are sol
knowledgeable yet lack the common sense to conceptualize the problem as it
really exists.

So you are saying that you can achieve 30km at 10GHz to a hand held receiver
at ground level with a 300 foot hill in the way!!! I am sure that you could
not do this with any sensible power even at 2m let alone 10GHz.

Perhaps it is your concept of what is going on that is wrong. Have you heard
of Fresnel Zones??
When obstructions come within the first Fresnel zone significant attenuation
occurs.

With the situation that you are describing the path is totally obstructed,
with the path only possible due to diffraction from the hill top. The hill
top impinges to at least the top of the 5th Fresnel Zone, hence the
attenuation is very high.

As the height of the Rx antenna increases the attenuation is still very high
until the hill top only start to intersect with of the first zone (antenna
height~150m). It then drops quite rapidly until there is true line of sight
and bottoms out when the hill top is clear of the second zone.

You make a great deal of the hill only being 0.006 degree at the horizon. If
you plot it accurately and with reference to the Fresnel zones, it does make
a big difference. With the Rx antenna at ground level the top of the Fresnel
zones are never below the horizon, which is completely different to the
situation when the hill is there (-5th Zone obstructed).

Also, without the hill you only have to raise the Rx antenna to about 15m to
achieve line of sight compared to 200m with the hill there!!!!!! Quite a big
difference I think you will agree, and one that your 'conceptualisation
doesn't seem to allow for!!

73
Jeff

wrote in message
oups.com...
hello
Jeff
i am very thank full to your help, i have got Rx height 101.2

Regards
naqvi

Please show your work.

"Stefan Wolfe" wrote in message
...

wrote in message
oups.com...
hello
Jeff
i am very thank full to your help, i have got Rx height 101.2

Regards
naqvi

Please show your work.


Hi Stephan

Your posts seem to inply that the receive antenna will "see" the 20 meter
high transmitting antenna when the receiver antenna is in the shadow of the
80 meter hill. It seems that the receiver needs to be out of the shadow of
the hill unless you are able to estimate refraction from the hill.

But, your aparent confidance in the statement "0 feet" makes me wonder if
I have this problem wrongly analyzed. I have so much confidance in Richard
Fry's data that I had accepted his estimation of 270 meters to be as close
as you can estimate.

Do I misunderstand your post about what minimum height is needed?

Jerry

"Jerry Martes" wrote in message
news:iLuyh.5336$384.156@trnddc05...

"Stefan Wolfe" wrote in message
...

wrote in message
oups.com...
hello
Jeff
i am very thank full to your help, i have got Rx height 101.2

Regards
naqvi

Please show your work.


Hi Stephan

Your posts seem to inply that the receive antenna will "see" the 20
meter high transmitting antenna when the receiver antenna is in the shadow
of the 80 meter hill. It seems that the receiver needs to be out of the
shadow of the hill unless you are able to estimate refraction from the
hill.

But, your aparent confidance in the statement "0 feet" makes me wonder if
I have this problem wrongly analyzed. I have so much confidance in
Richard Fry's data that I had accepted his estimation of 270 meters to be
as close as you can estimate.

Do I misunderstand your post about what minimum height is needed?

Jerry
Hi Jerry,

how many shadows have you seen that are 20Km long?

From: "Stefan Wolfe"
how many shadows have you seen that are 20Km long?
______________

Can we count the shadow of the moon on the earth during a
fully-eclipsed sun?

If so, that's a bit more than 20 km.

RF

"Stefan Wolfe" wrote in message
...

"Jerry Martes" wrote in message
news:iLuyh.5336$384.156@trnddc05...

"Stefan Wolfe" wrote in message
...

wrote in message
oups.com...
hello
Jeff
i am very thank full to your help, i have got Rx height 101.2

Regards
naqvi

Please show your work.


Hi Stephan

Your posts seem to inply that the receive antenna will "see" the 20
meter high transmitting antenna when the receiver antenna is in the
shadow of the 80 meter hill. It seems that the receiver needs to be out
of the shadow of the hill unless you are able to estimate refraction from
the hill.

But, your aparent confidance in the statement "0 feet" makes me wonder
if I have this problem wrongly analyzed. I have so much confidance in
Richard Fry's data that I had accepted his estimation of 270 meters to be
as close as you can estimate.

Do I misunderstand your post about what minimum height is needed?

Jerry
Hi Jerry,

how many shadows have you seen that are 20Km long?


Hi Stephan

Tell me where I have misunderstood the problem. I assumed the
transmitting antenna was Lower than the top of the hill. But, you seem to
imply that the transmitter can be seen even when the hill is blocking the
"view" to it.

I have actually never measured a shadow longer that a few feet, but I
assumed they continued to exist to infinity when an object blocks them from
view.

Jerry

"Jerry Martes" wrote in message
news:2Yvyh.37369$5U4.35764@trnddc07...

"Stefan Wolfe" wrote in message
...

"Jerry Martes" wrote in message
news:iLuyh.5336$384.156@trnddc05...

"Stefan Wolfe" wrote in message
...

wrote in message
oups.com...
hello
Jeff
i am very thank full to your help, i have got Rx height 101.2

Regards
naqvi

Please show your work.


Hi Stephan

Your posts seem to inply that the receive antenna will "see" the 20
meter high transmitting antenna when the receiver antenna is in the
shadow of the 80 meter hill. It seems that the receiver needs to be out
of the shadow of the hill unless you are able to estimate refraction
from the hill.

But, your aparent confidance in the statement "0 feet" makes me wonder
if I have this problem wrongly analyzed. I have so much confidance in
Richard Fry's data that I had accepted his estimation of 270 meters to
be as close as you can estimate.

Do I misunderstand your post about what minimum height is needed?

Jerry
Hi Jerry,

how many shadows have you seen that are 20Km long?


Hi Stephan

Tell me where I have misunderstood the problem. I assumed the
transmitting antenna was Lower than the top of the hill. But, you seem
to imply that the transmitter can be seen even when the hill is blocking
the "view" to it.

I have actually never measured a shadow longer that a few feet, but I
assumed they continued to exist to infinity when an object blocks them
from view.

Well you see Jerry, the reason you only see it for a few feet is because the
attenuation of the light varies inversely with the distance from the object
that blocks the light. I think you have done a good job in making my point.
Thanks,