[aprssig] Field Day ISS APRS Contacts? Doppler
Lynn W. Deffenbaugh (Mr)
ldeffenb at homeside.to
Wed Jun 20 13:58:24 CDT 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
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
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>> aprssig at tapr.org
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