What is the Maximum Range I can Get?

[abcd567]

INTRODUCTION
The Maximum Range achievable at any location depends on
(1) Curvature of earth
(2) The  terrain around that location. Terrain plays a very important role as hills & changes in ground level will restrict maximum range.

This is due to the fact that propagation of radio waves in GHz/Microwave range is line of sight. The range is therefore limited by curvature of earth, and is about 250 nautical miles / 450 km for an ideal condition of perfectly level terrain. Hills &  rise in ground levels further restrict maximum range to less than 250 nautical miles / 450 km.

FIND YOUR MAXIMUM POSSIBLE RANGE
In order to determine what maximum possible range you can get at your location, follow the steps below:
(1) Visit the site http://www.heywhatsthat.com
(2) Select tab "new panorama"
(3) Enter your latitude and longitude
(4) Enter your elevation (=enter elevation of your antenna)
(5) Enter title
(6) Hit "submit request" button
(7) Wait and view sponsor's advertisement while panorama is generated
(8) When panorama is generated, scroll down to map, and click "up in the air" tab on top right of map.
(9) Zoom-out the map till you see two circular curves in blue & yellow colors, showing maximum distance of aircrafts at 10,000 feet & 30,000 feet elevation.
(10) Below the map you will see text boxes light yellow & light blue with default aircraft heights 10,000 feet & 30,000 feet. Change these to suite your requirements, and press "Enter" button. The two curves will modify to new height figures you have entered. I recommend to use 10,000 & 45,000 feet, as normally commercial flights are 45,000 feet & below.








REFRACTION OF RADIO WAVES
The layers of air cause refraction of radio waves, and radio line of sight may extend beyond optical line of sight by as much as 50 to 100 nautical miles. Your maximum possible range therefore may be up to about 50 to 100 nautical miles more than the maximum possible range shown by the curves you got from heywhatsthat.com site.






ANTENNA LOCATION
To achieve your maximum possible range, your antenna should be installed at a height where it is above trees & houses surrounding it, and can "see" the horizon.


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[neroon79]

Some additions to abcd567's post.

The maximum range depends on antenna hight, airframe altitude and atmospheric condition.

The additional range in standard atmosphere due to atmospheric refraction with an antenna mounted 2m above any nearby obstacle is 30nm for airframes at 32000ft (FL320) an 35nm for airframes at 45000ft (FL450).

As the refraction varies with temperature, pressure and moisture the range can and will vary several nautical miles, in some cases even throughout the day.

If the website heywhatsthat.com takes the visual  atmospheric refraction into account while calculation the range rings, the additional range for received airframes will be much lower than 30nm to 35nm. The addition in range above the visual range after refraction correction is only 11nm (FL320) to 13nm (FL450).

Ingo

[abcd567]

@neroon79

Hi Ingo
Thanks for pointing out about refraction.
The default refractive index used by "heywhatsthat.com" is 0.14, which is used for visible light.
The recommended refractive index for microwaves is 0.25

The results obtained by using refractive index for microwaves are only slightly different from visual range and are only a conservative/average value.


If any one wants to get his curves for microwave recommended refractive index of 0.25, he has to enter the "heywhatstha.com" site using the following link:

http://www.heywhatsthat.com/?refraction=1

When you go to "New Panorama" page through the above page, you will find there an extra option to enter the desired refractive index.

5. Optional parameters:
Refraction     .....
   Leave blank for default of 0.14


The real increase comes with atmospheric conditions like temperature, humidity etc. These atmospheric conditions fluctuate, and often result in range increase more than 50nm. This is the reason I have used a figure of extra 50nm to 100nm in my first post. This is confirmed by my practical observation. My maximum range for 40,000 ft elevation is about 260 nm in the best direction, but often I get planes up to 300 nm, and occasionally up to 355 nm. Please see screenshot below. The two irregular rings are heywhatsthat.com range rings for elevations 10,000 ft and 40,000 feet, refractive index 0.25.
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[neroon79]

Sorry abcd, that's what I would call a false proof.

It's more likely that these 300nm+ receptions are caused by receiving of corrupted data packets* than by additional range due to atmospheric conditions. As a matter of fact these effects are only valid for HF and partly for VHF radio signals. But it doesn't work with UHF signals like ADS-B transmissions. Espsecially due to the fact that ADS-B is a digital databurst with relatively wide bandwidth.

Another reason can be the reception of surface reflected/diffracted signals. These can be identified if "overrange" receptions are always happening in the same direction.

*Bit change in a way that the checksum of  Error correction is still valid/true. Occurance increases with number of airframes in range.

Ingo

[pramodhbraj]

Very Helpful Post!

[TomNJerry]

Moderator:

This very useful thread was created 4 years ago.
Why it is not made sticky yet?

Making it sticky will benefit a very large number of members of this forum.