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Re: 400.1 MHz again ...



AS an ex Submarine navigation ET of 22 years, I have listed to more than a
few Transit passes.  The Transit satellite, when operating properly, was a
carrier only.  At the even minute that was a "Barker word" that was
transmitted.  This was the orbital elements/almanac for all satellites in
the constalation.  The computer used the Barker Word to determine time, you
had to know time within one minute to track a pass.  The computer used the
doppler shift of the carrier to compute latitude and longitute offsets.
The computer would first generate a set of expected doppler curves for
where the nav system thought it was.  The doppler curves obtained from the
navsat were overlayed in the computer.  The difference in the curves
represented the LAC and LOC.  The Navsat used two channels one at just
below 150.00 MHz (149.995 I think) and one just below 400 MHz (399.995 I
think).  The two channels improved the fix accuracy to eliminate
difraction, refraction and containment due to the difference in propagation
properties of the two frequencies.  

I do not remember the type of modulation for the Barker word.  It sounds
like a short duration data burst tone through the headset.

Just for information.  And BTW the Coast Guard says the Transit system has
been turned off.  I found this out after I bought a Magnavox Navsat
receiver at a local pawn shop.  This was a commercial receiver and used the
400 MHz channel only.

73

Glenn
WB4UIV

At 09:36 PM 1/6/00 +0100, you wrote:
>As far as i remember, the Transit carrier were psk modulated and carried
>the orbital elements of the sat as well as the almanach. F  was 150 and
>400.00 Mhz. After check it seems that telemetry from orbcomm is on
>400.1.
>Ghis,
>
>Satedu Team.
>
>Richard Allen wrote:
> > 
> > my original message:
> > 
> > > Can anyone tell me what satellites are transmitting
> > > what appear to be unmodulated carriers on 400.1 MHz
> > > +- > 7 kHz of Doppler?  There appear to be many LEO
> > > birds transmitting.
> > 
> > Thanks to the 25 or so folks that replied so far.
> > 
> > They are definitely not TRANSIT since the carriers are never
> > modulated.  Evidently Iridium and Teledesic are out.  One
> > reply said ORBCOMM with what appeared to be certainty and
> > another two blamed the Russian navsats.
> > 
> > Richard  W5SXD ...
> > 
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>
>-- 
>______________________________
>Ghislain RUY 
>F1HDD/ON1RG
>---
>SATEDU TEAM
>______________________________
>
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>
>
---------------------------------------------------------------------------
Glenn Little                         glittle@awod.com   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv@amsat.org   AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)                      ARRL  TAPR
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