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Author Topic: line of site  (Read 7940 times)

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Airmad

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line of site
« on: April 24, 2008, 02:24:41 PM »
I am wondering if signels are reflecting off something as there is no way i have line of site
to east midlands airport. have high buildings in that direction but look at alt from aircraft ???

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steveb25

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Re: line of site
« Reply #1 on: April 24, 2008, 02:36:13 PM »
I would imagine that the frequencies that are being used for this system would not allow bouncing of solid objects. They usually get absorbed.

Do you get this kind of reception all the time or could it be atmospheric?

Airmad

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Re: line of site
« Reply #2 on: April 24, 2008, 02:50:34 PM »
I would imagine that the frequencies that are being used for this system would not allow bouncing of solid objects. They usually get absorbed.

Do you get this kind of reception all the time or could it be atmospheric?
No  steve most of the time. but real radar do's refect off aircraft but do not know at what frequency radar works on

Allocator

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Re: line of site
« Reply #3 on: April 24, 2008, 02:50:51 PM »
I am wondering if signels are reflecting off something as there is no way i have line of site
to east midlands airport. have high buildings in that direction but look at alt from aircraft ???

The aircraft is about 2 miles finals, and on a 3 degree glidepath it would be at 600 ft above ground level.  East Midlands is 300 ft above mean sea level, so if you had the correct QNH set in RadarBox, the aircraft should be indicating about 900 ft on the map.

Did you use the airfield/QNH autoset in the SmartView tab?

Even so, seeing the aircraft down to 600 ft agl is still pretty good :-)

Airmad

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Re: line of site
« Reply #4 on: April 24, 2008, 02:59:09 PM »
I am wondering if signels are reflecting off something as there is no way i have line of site
to east midlands airport. have high buildings in that direction but look at alt from aircraft ???
how do i set qnh nt sure of this

The aircraft is about 2 miles finals, and on a 3 degree glidepath it would be at 600 ft above ground level.  East Midlands is 300 ft above mean sea level, so if you had the correct QNH set in RadarBox, the aircraft should be indicating about 900 ft on the map.

Did you use the airfield/QNH autoset in the SmartView tab?

Even so, seeing the aircraft down to 600 ft agl is still pretty good :-)

Airmad

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Re: line of site
« Reply #5 on: April 24, 2008, 03:13:50 PM »
 have i set QNH correct now (Sorry not very good at replying yet)

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Allocator

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Re: line of site
« Reply #6 on: April 24, 2008, 03:20:07 PM »
have i set QNH correct now (Sorry not very good at replying yet)

It will be interesting to see what the aircraft are showing on the map now.

Your previous picture showing the aircraft at 95 ft and if the actual QNH of 1016 mb, would indicate that you had 989 mb set before (or thereabouts - if I've got my maths right!)

"Wind on millibars, wind on height"

ac 900 ft amsl

indicating 95 ft

900-95 = 805 ft

805/30 = 26.8  (say 27 mb to keep things simple and 1 mb =30 ft)

Actual QNH = 1016

1016-27 = 989 mb

So if QNH set was 989 to show 95 ft

wind on mb (increase) to 1016 and height winds on (increases) to 900 ft

« Last Edit: April 24, 2008, 03:44:25 PM by Allocator »

steveb25

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Re: line of site
« Reply #7 on: April 24, 2008, 03:57:39 PM »
Airmad

The frequencies that radar's work on is a closely guarded secret, especially the ones that the military use.

I agree that radar does reflect, otherwise the ground stations would not receive a return from the aircraft, hence radar would be useless. What I was trying to say is that these emissions are from the aircraft so even at 600-900ft would would still get something.

Just to say that at 1.09Ghz the frequency being used are very short wave signals and do get absorbed by things very easily, therefore I doubt you are getting reflections

Airmad

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Re: line of site
« Reply #8 on: April 24, 2008, 04:12:54 PM »
Thanks allocator for all your help. No aircraft landing at the moment. but this is my polar diagram just for your interest.

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Airmad

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Re: line of site
« Reply #9 on: April 24, 2008, 04:52:11 PM »
Thanks allocator for all your help. No aircraft landing at the moment. but this is my polar diagram just for your interest.
Thanks steve understand. i have some nice radios like to listen to aircraft on shortwave 5616Khz atlantic flight, but not much on vhf/uhf only east midlands on 124.000Mhz tower and 134.175 approach
« Last Edit: April 24, 2008, 05:00:04 PM by Airmad »

WiMo

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Re: line of site
« Reply #10 on: April 25, 2008, 07:31:46 AM »
I am wondering if signels are reflecting off something as there is no way i have line of site
to east midlands airport. have high buildings in that direction but look at alt from aircraft ???

High frequency and love go strange ways.

Yes, these signals can be easily reflected (although partially) by buildings with even surfaces, but also by ionospheric effects. We have seen signals many 100 miles distant due to athmospheric inversion layers, I personally experienced on several occasions reflections which led to very surprising signals.

Rgds,
Ekki/WiMo

Airmad

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Re: line of site
« Reply #11 on: April 25, 2008, 09:20:54 AM »
THANKS Ekki/Wimo. had an idea they did all the best Tony