# [amsat-bb] Doppler effect

Daniel F6CDZ daniel.f6cdz at orange.fr
Sat Jan 9 01:16:53 PST 2010

```Hello to all.
My little contribution for an explanation about the doppler effect....
73, Daniel F6CDZ loc: JN39BE

Doppler effect

The Doppler effect is an immediate gap of the received frequency when the distance varies between the point of broadcast and the point of reception.
The variation of frequency depends on the relative speed of link or on estrangement between the satellite and the station ground, of the angle of movement and the emitted frequency.

The Doppler effect varies with the position of the satellite on its orbit, because the relative speed varies with this position.
The frequency increases when the satellite approaches, it decreases when it goes away from the observer.

The "simple" formula is :

F real = F nom (1 + V/C)

V = relative speed of the sat on Km/s

C = light speed (300.000 Km/s)

1+ or 1- depending of the direction sat/operator (to the operator or from the operator)

Mode NORmal  and  REVerse :

¾ NOR        : if I increase 1 KHz on VHF, the UHF increases also of 3 KHz => total gap (+1 + +3) = + 4 KHz

¾ INV(REV)   : if I increase 1 KHz on VHF, the UHF decreases of 3 KHz => total gap (+1 - 3) = - 2 KHz
```