Radar Range...

[mlhifi]

I live in the North West UK, on the Wirral Peninsular. For the last few days, any air traffic that "drops" below 2400 feet are not showing. I therefore assume that a receiver in the area is switched off, or faulty.
So, a more distant receiver is picking up the signal when the aircraft gets above a certain height! How far away from me is that receiver likely to be? I know it depends on aerial height etc, but as a rough idea? Are we talking 5, 10, 100, 200 miles? Based on the answer, this determines how many receivers we need to give 100% coverage down to ground level.
When I can afford a receiver, rest assured I will do my best to keep it on 24/7. I would love to know where the nearest receiver is to me actually... anyone?
Regards,
Mike

[Anmer]

The Net2 feed has a receiver based near Liverpool which may have been offline.

ModeS data is line of sight. The receiver that's picking up data above 2,400 feet could be anywhere. I can see aircraft down to 4,000 feet at London Heathrow from 90 miles away, but so too could any receiver between me and Heathrow.

You may find this calculator of help:

http://radarproblems.com/calculators/horizon.htm

This calculates that a target at 2,400 feet can be picked up as far away as 60 nm (or nearer). Assumes no obstacles to block the signal. such as hills or buildings.

[mlhifi]

The Net2 feed has a receiver based near Liverpool which may have been offline.

ModeS data is line of sight. The receiver that's picking up data above 2,400 feet could be anywhere. I can see aircraft down to 4,000 feet at London Heathrow from 90 miles away, but so too could any receiver between me and Heathrow.

You may find this calculator of help:

http://radarproblems.com/calculators/horizon.htm

This calculates that a target at 2,400 feet can be picked up as far away as 60 nm (or nearer). Assumes no obstacles to block the signal. such as hills or buildings.

I couldn't have asked for a better or more concise answer. Thank you, very much appreciated.
Very handy calculator too.
Regards,
Mike

[andbur]

Rough Calculation line of sight and other range factors

The formula to calculate the distance of the line of sight is:

Distance NM = Square Root of the Altitude in feet times 1.25
Here some samples

2.000 feet = 45 times 1.25 = 56 NM
5.000 feet = 71 times 1.25 = 88 NM
10.000 feet = 100 times 1.25 = 125 NM
20.000 feet = 141 times 1.25 = 181 NM
30.000 feet = 173 times 1.25 = 216 NM

The next consideration is where the transponder antenna is placed on the aircraft.
Most of the aircraft have this antenna underneath the fuselage, some have it on top of the cabin - some even have it placed somewhere on the wings. The position for it is choosen at installion on this specific aircraft - is dependant on other systems operating on or near the same frequency that may disturb this specific antenna - and - if more than one transponder system is installed. The idea is to reduce possible interference with other systems.

With changing of pitch and bank the antenna could be shielded off - and - the signal may disappear for some time. This may also happen in rare occasions when, due to the position of the aircraft in relation to the antenna the transponder antenna is shielded.

Greetings

Andreas