Re: [amsat-bb] AO-27 Freq, and my first AO-27 QSO

["KF4FDJ (Mike in Ft. Myers, FL)" <seven77@xxxxxxxx>]

Hi John,

John Mock wrote:
> Please do NOT attempt to correct for doppler on AO-27 uplink.  The satellite
> has a wideband receiver and takes care of that for you.  When one does so,
> it increases (doubles??) the amount of bandwidth that AO-27 consumes on the
> uplink in the 20 KHz wide 2m space sub-band. It is required for UHF uplinks,
> such as the MIR/SAFEX repeater [SK??], but not for AO-27.
 
?????

I really don't understand what you are stating here.  Doppler shift on a
rapidly moving object is a reality based on the laws of physics. 
Correcting for Doppler is NEVER wasteful, but makes good sense.

If my HT was capable of tuning steps smaller than 5 kHz, then I would
constantly compensate for Doppler on both uplink and downlink, much as I
do on my home based Oscar station.  As it is, an HT user is well served
by the 5 frequency pairs I posted originally:

>     436.805 - 145.845
>     436.800 - 145.850
>     436.795 - 145.850  middle of pass
>     436.790 - 145.850
>     436.785 - 145.855

The nominal center of the pass band and Doppler shift on AO-27 are: 
	Uplink 145.850 MHz +/- 3.5 kHz
	Downlink: 436.792 MHz +/- 10 kHz

So, if I wanted to tune the center of the transmitted signal at AOS, I
would have my receiver set to 436.802.  If I also wanted my signal close
to the center of the satellite receiver pass band, I would tune down 3.5
kHz and transmit on 145.8465. 

Especially if I am accessing the bird with a low ERP, concentrating my
uplink signal at the center of the sat receiver pass band will help
guarantee my success.

The receiver pass band on AO-27 is sufficiently wide that it WILL hear
my signal if I don't compensate for Doppler, but if I am competing with
other signals, at times I need every advantage.

I am not using any more bandwidth, and am not being wasteful.  Whoever
told you that John must have been pulling your leg.

73, Mike in Fort Myers, FL

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