[amsat-bb] EO-80 FM Transponder doubt

Greg D ko6th.greg at gmail.com
Mon Jun 22 01:56:58 UTC 2015

Yes, Pavel, but since the frequency heard by the satellite as it 
approaches is higher than what you sent, you need to send at a lower 
frequency to compensate.  The idea is that you want the frequency heard 
at the satellite to be constant.

As the satellite passes the midpoint, and recedes from view, the 
frequency it hears is lower than what you transmitted.  So you need to 
send at a higher frequency to compensate, again so that the satellite 
hears a constant signal.

So, during the pass your transmitter needs to go from lower to higher.

The physics works the same for your reception (it better!), but since 
the satellite isn't changing its frequency to be constant at your end, 
you need to move from higher (on approach) to lower (towards LOS) to 

Greg  KO6TH

Pavel Milanes Costa wrote:
> I have a doubt...
> A few days ago Paul put a list of the proposed channel for EO-80..
> I have noted that the TX freqs are from lower to higher (AOS to LOS), 
> is that correct?
> From the sat point of view a Tx on the center freq will appears as 
> shifted up at the AOS because the two point are getting closer 
> (doppler is summing), in fact no matter is the freq is for TX or RX if 
> at AOS the shift must be + not -
> I'm right?
> PS: with the 2.5 Khz of the new Chinese radios the 2m downlink can be 
> shifted to +2.5 Khz at AOS and -2.5 Khz at LOS to improve reception 
> quality
> El 17/06/15 a las 12:59, Paul Stoetzer escibió:
>> Anyone who wants to program memories for EO-80 should follow this plan:
>> EO-80 AOS - TX 435.070 MHz 210.7 Hz CTCSS, RX 145.840 MHz
>> EO-80 2      -  TX 435.075 MHz 210.7 Hz CTCSS, RX 145.840 MHz
>> EO-80 TCA  -  TX 435.080 MHz 210.7 Hz CTCSS, RX 145.840 MHz
>> EO-80 4      -  TX 435.085 MHz 210.7 Hz CTCSS, RX 145.840 MHz
>> EO-80 LOS -  TX 435.090 MHz 210.7 Hz CTCSS, RX 145.840 MHz
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. 
> Opinions expressed
> are solely those of the author, and do not reflect the official views 
> of AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite 
> program!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb

More information about the AMSAT-BB mailing list