Line of sight/altitude

[bratters]

Obviously there is a correlation between height and distance as regards signal reception but has anybody got any "rule of thumb" advice as to the relationship between altitude and distance?

For example if I have a clear (ish) field of view from my top window with a 100 mile fairly flat run topographically speaking, what would be the minimum altitude at which an aircraft would have to be at a given distance for me to reasonably expect to receive a signal?

I would like to establish some correlation between my radar ring settings and altitude.

Any mathematicians out there?

[MrT]

There is a formula around somewhere for calculating this. I'll try and dig it up.

[tarbat]

Look at http://www.airnavsystems.com/forum/index.php?topic=3335

Describes a website that lets you enter your location, and see the line-of-sight at differetnt altitudes.

Website is at http://www.heywhatsthat.com/main-0904.html

For example, here's what it predicts I should be able to see at FL100 (black line) and FL350 (blue line).

[radarspotter10]

There is a formula around somewhere for calculating this. I'll try and dig it up.

hi bratters
I would say on my own experience i get say around 200miles steady , but i have seen flights 350 miles away
sometime more, there a thing called propagation, its a thing thats always interested me since my c.b. days talking from Ireland to  new zealand.
Would love to see posts from airnav users just to see how far they can get.
One last note, i have seen in the last say days the contrails left by aircraft was little
or 0, but this morning there miles long, i know this have something to do with contrails being composed of ice particles, would this affect radio waves.
more question than answers this morning
from pat enjoying my airnav

[MikeC]

Tarbat, what's blocking your view to the east?  I thought you had an ocean view in that direction?  I'm probably reading thsi wrong?

[tarbat]

Tarbat, what's blocking your view to the east?

The bit of Knockshortie Hill that's near our house.   The nearer a hill is, the more it mask line-of-site.

In fact, that original chart didn't allow for the height of my antenna in the loft.  I've redone it, so look for the Tarbat panorama at http://www.heywhatsthat.com/main-0904.html

[RodBearden]

Tarbat's two pics really show the importance of aerial height in improving reception.

Rod

[tarbat]

Tarbat's two pics really show the importance of aerial height in improving reception.

Yes.  The difference between the two charts is approx. 20ft of extra antenna height.  And for comparison, my actual coverage by altitude - http://www.tarbat.gofreeserve.com/polar.htm

[MikeC]

Thanks Tarbat, very helpful.

[palmar]

Tarbat,

a short tutorial how to generate the plot?

3NM

[flightchecker]

As “gray is all of the theory”, line of sight calculations might be interesting, anyhow one should not  spend too much efforts respectively, as many factors will influence the validity of such a prediction, while disapointment might be preprogrammed if compared to the reality: antenna characteristics, cable & connector losses, propagation variing with weather condition, athmosperical refraction, signal reflections resulting in multipath propagation, (adding to or substracting from the “direct way” signal strength) seasonal effects due to the trees leaves, attenuating a signal more or less. Even the aircrafts bodyshape influencing a transponders signal radiation. There’s even more to the above.
Why not just stick the antenna out “at its best”, use a “plotter” to create  range vs altitude plots and then “see what you get”. It might be more, it might be less as compared to a theoretical calculation, but will tell the truth.

Regards

Karl

[bratters]

Why not just stick the antenna out “at its best”, use a “plotter” to create  range vs altitude plots and then “see what you get”. It might be more, it might be less as compared to a theoretical calculation, but will tell the truth.

Regards

Karl

It's the "truth" that's worrying me Karl!!
Volumes seem well down and I'm getting a bit worried about the box. Tried alternative aerials but same results. Could undoubtedly be due to seasonably reduced traffic, propogation or whatever but numbers are definitely down by up to 50%.

Distances are also down though not to the same extent. Almost as if the box was selecting random flights - picking up some and ignoring others. Definitely not the same symptoms as a front-end filter problem - which I've had in the past.

We'll plod on for a bit and see what transpires.

Thanks to all who replied. The formula(s) for height/distance are straightforward enough, but measuring the effect of intervening obstructions is a bit more tricky.

[tarbat]

Tarbat,

a short tutorial how to generate the plot?

Rod gave some instructions in the thread I linked to - http://www.airnavsystems.com/forum/index.php?topic=3335.  Haven't got time at the moment to do anything else.

In fact, I may be missing from these forums for a few weeks due to other family priorities.