Order Tray | Contact Us | Home | SIG Lists

[aprssig] Field Day ISS APRS Contacts? Doppler

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Jun 20 18:58:24 UTC 2012


Let me take a mental guess at this one....

The satellite is coming towards you very fast, squishing its transmitted 
waves and making it appear to be a higher frequency that you need to 
tune to hear it.  When the satellite is going away from you, the 
frequency lowers (think train whistle doppler to a stationery listener), 
so you need to tune lower than it is transmitting so you can catch it.

Now, for it to hear you, when it is coming towards you, your waves are 
going to a higher frequency so you need to transmit lower in order to 
hit it at the frequency at which it is listening.  When it is going away 
from you, it's now hearing the lowered frequency so you need to transmit 
higher so that you hit where it's listening.

Lynn (D) - KJ4ERJ - Yes, I puzzled this one mentally when I read it as 
well...

On 6/20/2012 2:52 PM, Dave wrote:
> How can they be in opposite directions? ?
>
> Bob Bruninga<bruninga at usna.edu>  wrote:
>
>>> I have made a few attempts and managed to copy one
>>> weak beacon packet. I was at 437.550 +- doppler.
>>> It is not easy like the vhf packet was.
>> And remember TX Doppler is in the opposite direction of RX Doppler.  So you
>> need 5 memories:
>>
>> RX 437.560  TX 437.540  Approaching
>> RX 437.555  TX 437.545
>> RX 437.550  TX 437.550  Closest point
>> RX 437.545  TX 437.555
>> RX 437.540  TX 437.560  Receeding
>>
>> Bob
>>
>>
>> _______________________________________________
>> aprssig mailing list
>> aprssig at tapr.org
>> https://www.tapr.org/cgi-bin/mailman/listinfo/aprssig
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> https://www.tapr.org/cgi-bin/mailman/listinfo/aprssig
>




More information about the aprssig mailing list