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Re: Help with AO-16 and "reverse tracking"



By the sounds of it, you'll just need to get some practice tuning for 
doppler on the AO-16 downlink.  For this sat, it is not even necessary to 
use doppler correction for your transmitter, but the FM might sound a little 
clearer, if you do.  No need to make things harder than they need to when 
yo're just getting started!

You can use either LSB or USB for listening to AO-16, but they will sound 
very different.  listening to LSB with no doppler-correction causes tones to 
go UP  in frequency as the sat passes, where they go DOWN when using USB. 
Either way, your receiver should be tuning downward all throughout the pass.

You will have to manually center your receiver before applying 
doppler-correction as you will need to be within 100Hz of the actual signal 
to hear the audio correctly.  The computer can't get it fine enough on it's 
own.  Also, of note, the speed of the doppler-shift is orders-of-magnitude 
faster while the satellite is directly overhead, compared to when it is 
aproaching or receding.  This is less-pronounced when the satellite pass is 
not directly overhead, but accross your horizon, and is much easier to track 
on these lower passes.

I have no automated doppler-correction, so I can only suggest what works for 
me... AO-16, when not in use, sends a constant tone.  You can use this tone 
to center your receiver at first, or if you get lost during the pass.  Just 
set your receiver to USB, and then look for the tone.  The tone should be 
around 30-60 Hz in order for the audio to be heard.  I think you will find 
that you can hear yourself talking when this tone is anywhere below 60Hz. 
You can test your computer's doppler-correction too, by seeing how well it 
follows this tone during a quiet pass. If you have only basic antennas, you 
won't need to send any more than 20 watts to hear yourself, unless, maybe if 
it's almost directly overhead and you're using vertical-omni's.  With better 
antennas, you might as well just crank your power all the way down, this is 
a VERY sensitive satellite!  One last thing: the tone will shift, or 
disappear completely when you key your transmitter -it's a nice clue that 
the sat is hearing you, when this happens on-cue.

Enjoy!

73's
Auke
VE6PWN
DO33go


----- Original Message ----- 
From: "Rick Mann" <rmann@latencyzero.com>
To: "AMSAT-BB Org" <amsat-bb@amsat.org>
Sent: Monday, March 17, 2008 5:13 PM
Subject: [amsat-bb] Help with AO-16 and "reverse tracking"


> Hi. I'm pretty new to all this. I've had one successful contact in my
> life (with ISS, no less!), but I decided last night to try AO-16. I
> have an ICOM IC-910H. I put it into satellite mode, and set it up to
> receive LSB/USB on 437.0260 MHz, and transmit FM on 145.9200 MHz.
>
> One thing the IC-910H instructions said to do is transmit a tone (like
> a whistle) and be sure one can receive that. After listening for some
> time (to a nearly overhead pass), at 5am, I tried doing that. Now, I
> *think* I heard myself, but a weird thing was if my whistle tone got
> lower in pitch it sounded higher. Not sure if that was just my
> imagination.
>
> In any case, MacDoppler seemed to be changing frequencies differently
> for transmit vs. receive. The 910H's manual talks about reverse
> tracking, where doppler on receive goes up while it goes down on
> transmit.
>
> Could someone clarify these things for me? Why would they be different?
>
> Thanks!
>
> -- 
> Rick
>
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