Doppler Shift and VO-52 Satellite

One of the critical aspects of Bird Tracking is handling of Doppler shift during the pass of satellite in your area. 

1. What is Doppler shift/Doppler Effect?

The Doppler effect (or Doppler shift), named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.

2. Why does it happen?

 

The relative increase in frequency can be explained as follows. When the source of the waves is moving toward the observer, each successive wave crest is emitted from a position closer to the observer than the previous wave. Therefore each wave takes slightly less time to reach the observer than the previous wave. Therefore the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wavefronts is reduced; so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wavefronts is increased, so the waves "spread out".

3. How to effectively handle the doppler shift for bird VO-52 (HAMSAT)?

The success of bird tacking depends on how effectively you tackle the doppler shift while satellite is approaching you and while it is moving away from you.

Below given is the table which explains you can tackle the doppler shift for VO-52 (HAMSAT) while up-linking (transmitting) on UHF 435.250 Mhz, Keep the downlink fixed at 145.900 Mhz. 

                                                    Uplink(Mhz)         Downlink(Mhz)

 

When Sat is approaching you-----    435.245

When Sat is nearer to you --------   435.250              145.900

When Sat is goes away from you-   435.255

The other way could be to keep the Uplinking frequency fixed at 435.250 and  shift the frequencies while as satellite approaches you as described below:-

                         Uplink(Mhz)         Downlink(Mhz)

 

                                                      145.905----When Sat is approaching you

                            435.250              145.900----When Sat is nearer to you

                                                      145.895 --- When Sat is goes away from you


As you get used to these shifting during the advanced stages you can shift both uplink and downlink simultaneously.

Happy Bird Tracking


73s


Next post i shall give the frequency shifts for AO-51

Five Steps to OSCAR Tracking

Article 2. OSCAR/VU2TQC/02/300710

Five Steps to receiving Satellite Signals (HAMSAT; VO-52)

Step 1. Note down the pass timings of VO-52 for the day , and focus on the passes having maximum elevation above 30 degrees (you may refer this blog or download satscape a free software from http://www.amsat.org), ensure that your are prepare and keep yourself ready atleast 15 minutes before the start of the satellite pass.

Step 2. Store the following frequencies in your VHF Rig (read your respective operating manuals)

145.890 MHZ
145.895 MHZ
145.900 MHZ
145.905 MHZ
145.910 MHZ
145.915 MHZ

You are storing these frequencies at a gap of 5khz to adjust the Doppler effect ( shall discuss this subject separately in another posting, but this will not hamper your current goal of satellite tracking)
Note: The downlink frequency band for VO-52 is ( 145.870 MHZ to 145.930 MHZ)

Step 3. Trigger your rig to check if your antenna (any fixed antenna which you have installed for regular VHF QSO) is triggering the repeater in your area, just to ensure your antenna feed-line is connected to your rig (at times due to excitement in the entire process we may miss out the connection).

Step 4. Start your monitoring of frequencies as mentioned in step 2 from 145.915 MHZ, and keep coming down by 5khz to 145.900 MHZ (be patient here you may not copy anything till the 2 to 3 minutes from the start timing of the satellite pass).

Step 5. Note down the call signs you hear ( you will hear the QSOs as clearly as your regular line of sight VHF QSOs ; the only difference is you may not see any pixels on the bar graph of your rig).
Note: Please make sure do not transmit (uplink) on these frequencies as it would not reach any where and jam the satellite band.