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RE: AMSAT has a SECRET!



> ------------ Original Message -----------
> From: Edward R. Cole <al7eb@ptialaska.net>
> Date: Fri, 01 Jun 2001 04:53:23 -0800
> 
> Maybe an idea that has not been voiced is the need to consider microwave
> Leo's to add to the current crop of Mode-A and Mode-B birds!
> 

Ed,

Given that Doppler Shift increases with increasing frequency and increases with increasing velocity, I imagine the doppler on microwaves on a LEO orbit would be rather large.  We can get away with it on AO-40 because at apogee, the bird appears to not be moving very fast at all.  But a LEO moves across the sky in less than 20 minutes.

Yes, there is automatic computer tuning and all that.  I KNOW some people will respond with that.  Sure, there is.  But if you don't have equipment that will do that, you will spend a lot of time spinning the dial I am afraid.

That's not to say that it won't work, it just might make operation difficult, particularly for those operators doing it "on the cheap."

OK, in the spirit of forward thinking for those who will say I am stuck in the past, let me offer up the following sort of idea to make microwaves easier:

Make the satellite digital.  It will send out its position calculated from a built in GPS receiver to your radio.  Your radio will have a wide-band IF mod and you will feed the audio level into your Windoze sound card.  Then your computer will take this information, calculate the doppler shift based on your location (also specified by GPS) and the calculate how much to turn your rotor as well as tune the radio.  It's all automatic then.  For that matter, the satellite will assign you a digital voice slot.  Then it will shift that digital voice slot at the satellite to accomodate the doppler shift.  In fact, the onboard DSP could do all this and adjust things so that you won't even really notice much doppler at all.  I can envision all sorts of ideas with this.  Of course, it will require the user to build several control boxes.  The user will have to use a specific type of computer that all the code is written for, etc.  But it could be done.

OK, seriously, it would be an interesting experiment to try SSB voice on a microwave LEO.  It would be fun although perhaps not the easiest to use.

73,

Jon
NA9D
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