[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

*Subject*: R: [amsat-bb] A doppler 2.4GHz question*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Fri, 17 Dec 2004 11:27:15 +0100

----- Original Message ----- From: Graham Shirville <g.shirville@btinternet.com> To: <amsat-bb@amsat.org> Sent: Thursday, December 16, 2004 9:28 PM Subject: [amsat-bb] A doppler 2.4GHz question > Hi All, > > We are still working on the possibility for a digital ATV installation for > the ISS and this would probably use the DVB-S system and have a downlink in > the 2400-2450MHz band. > > One of the questions being asked is about how robust the ground segment RX > system would be in the presence of the doppler shifts that occur at that > frequency. > > The next question that then comes is "what is the worse case - i.e. the > maximum rate of change" for the received frequency? > > Now I know this will be when the ISS is approaching TCA on an overhead pass > but I have no idea how to calculate the actual rate of change. > > Any help would be much appreciated. We know that Formula 1 racing cars > coming to sudden stops is not a problem for their headcams and other digital > cameras but this around a 700Hz per sec change and I suspect that we may be > an order of magnitude more than that! > > cheers and happy holidays! > > 73 > Graham G3VZV > ---- Hi Graham, G3VZV I selected the ISS Rev. numbar 34711 of today 12/17/2004 wich pass has a max elevation of 49.955° over Naples and using InstantTrak I have manually computed (T key) the range and elevation very close to my TCA at the following times with intervals of 1 second in between to calculate the speed of approach expressed in km/sec UTC =10:07:31 Elevation= 49.955° Range 1 = 462.156 km UTC =10:07:32 Elevation= 49.589° Range 2 = 464.427 km UTC =10:07:33 Elevation= 49.194° Range 3 = 466.486 km As you can see the ISS just started to go away from the point of closest approach TCA of my QTH going to LOS at the following speeds: Range 2-Range 1 = 2.271 km/sec Range 3-Range 2 = 2.059 km/sec Considering a frequency of 2400 MHz and the speed of light 299792 km/sec the doppler shift at 10:07:32 can be calculated as follows expressed in Hz 6 2400 x 10 x ( 2.271 / 299792 ) = 18180.60 Hz And after one second at 10:07:33 the doppler shift is: 6 2400 x 10 x (2.059 / 299792 )= 16483.42 Hz The rate of change of doppler shift at 2400 MHz expressed in Hz/sec for the above pass at TCA between 10:07:32 UTC and 10:07:33 UTC for the ISS is 18180.60 - 16483.42 = 1697.18 Hz/sec As you suspected the order of magnitude is more than 700 Hz/sec and for latitudes at wich a pass is more overhead the rate of change of doppler shift is even greater than 1697.18 Hz/sec Best 73" de i8CVS Domenico > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author. > Not an AMSAT member? Join now to support the amateur satellite program! > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org ---- Sent via amsat-bb@amsat.org. Opinions expressed are those of the author. Not an AMSAT member? Join now to support the amateur satellite program! To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**A doppler 2.4GHz question***From:*Graham Shirville

- Prev by Date:
**AO-51 schedule page update** - Next by Date:
**Re: AMSAT-BB-digest V2004 #499** - Prev by thread:
**Re: A doppler 2.4GHz question** - Next by thread:
**FOR SALE-W2IHY 8 Band Equalizer** - Index(es):