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" [email protected] To: "AMSAT-BB Org" [email protected] 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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