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Re: Radar Pings off ISS



Bob,

The frequency is 216.98 MHz. There are two other transmitters a couple of
KHz above and below the center frequency. These transmitters illuminate the
west and east sides of the US. They use lower power. I see objects all over
the place in frequency (+/- 10 KHz). I am using a 150 KHz spectrum span for
my captures. I analyzed my ISS recording after sending my previous message
and I actually found the ISS reflection at two of the frequencies. By
analyzing the Doppler curves for more than one transmitter, we can calculate
the satellite trajectory. I have posted a second image that shows the ISS
crossing the Texas and Alabama fences. There is a slight difference in the
timing and Doppler curves.

http://www.rfspace.com/ISS2.gif

Pieter, N4IP


----- Original Message -----
From: "Bob Bruninga" <bruninga@usna.edu>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, December 02, 2003 8:09 PM
Subject: Re: [amsat-bb] Radar Pings off ISS


> > Navy Satellite Radar at 217 MHz:
> >
> > On our third attempt we still havent heard anything other than computer
> > birdies...
>
> And I just figured out why!... Duh...
> I had figured that the +/- 5 KHz doppler all occured during a single
> ping (like it does for a typical LEO pass).. so exact tuning wasnt
> important....
>
> WRONG.  Now that I think about it, the instantaneous Doppler is only a
> function of WHERE and at what angle it goes through the fence and it does
> NOT go through the full 10 KHz on a pass like a normal horizon to horizon
> LEO pass goes.  We only hear 1 second of a reflection and the
> instantaneous Doppler change is insignificant during that instant.
>
> Bottom line.  We must ANTICIPATE the exact Doppler and pre-tune the
> receiver to exactly that correct frequency or we wont hear it at all...
> Cant wait to try again...
>
> Oh, and you have to vector sum the Doppler from you to the ISS and from
> ISS to SPASUR to get the right answer...
>
> Bob
>
>
> ----
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----
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