One of the concerns in tracking a balloon is the distance that a on-board transmitter needs to reach a listening (APRS) station. The table that follows shows the line-of-sight
distance to the horizon based on balloon altitude - assuming perfect
conditions. The formula is: distance
(miles) = 1.22 x SQRT (height in feet). A radio signal from a balloon payload
should be able to reach an APRS repeating station over 90 miles away at a height of 7,000 feet; and at 110,000
feet, an on-board transmitter has a line-of-sight of over 385 miles!
On the return trip down, a payload's radio signal should reach out as far as 29 miles at just 700 feet up, giving a
reasonable approximation of the touchdown location right up to landing!
Line of Sight Radio
Distance / Altitude
Altitude in Feet
|
Miles to Horizon
|
Square Miles Area
|
Altitude in Feet
|
Miles to Horizon
|
Square Miles Area
|
120,000
|
422.6
|
561,113
|
600
|
27.1
|
2,300
|
110,000
|
404.6
|
514,354
|
500
|
24.7
|
1,916
|
100,000
|
385.8
|
467,594
|
400
|
22.1
|
1,533
|
90,000
|
366.0
|
420,835
|
300
|
19.1
|
1,150
|
80,000
|
345.1
|
374,075
|
200
|
15.6
|
767
|
70,000
|
322.8
|
327,316
|
100
|
11.0
|
383
|
60,000
|
298.8
|
280,557
|
90
|
10.5
|
345
|
50,000
|
272.8
|
233,797
|
80
|
9.9
|
307
|
40,000
|
244.0
|
187,038
|
70
|
9.2
|
268
|
30,000
|
211.3
|
140,278
|
60
|
8.6
|
230
|
20,000
|
172.5
|
93,519
|
50
|
7.8
|
192
|
10,000
|
122.0
|
46,759
|
40
|
7.0
|
153
|
9,000
|
104.8
|
34,495
|
30
|
6.0
|
115
|
8,000
|
98.8
|
30,662
|
20
|
4.9
|
77
|
7,000
|
92.4
|
26,829
|
10
|
3.5
|
38
|
6,000
|
85.6
|
22,996
|
9
|
3.3
|
34
|
5,000
|
78.1
|
19,164
|
8
|
3.1
|
31
|
4,000
|
69.9
|
15,331
|
7
|
2.9
|
27
|
3,000
|
60.5
|
11,498
|
6
|
2.7
|
23
|
2,000
|
49.4
|
7,665
|
5
|
2.5
|
19
|
1,000
|
34.9
|
3,833
|
4
|
2.2
|
15
|
900
|
33.1
|
3,449
|
3
|
1.9
|
11
|
800
|
31.2
|
3,066
|
2
|
1.6
|
8
|
700
|
29.2
|
2,683
|
1
|
1.1
|
4
|
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