[aprssig] PCSAT2 Downlink Challenge

[Robert Bruninga]

When PCSAT2 is enabled on Monday or Wednesday,
(1,3 Aug) we'd like to capture as much of the 
1200 baud and 9600 baud telemetry on 437.975
MHz as possible.  See the plan on:
http://www.ew.usna.edu/~bruninga/pec/pc2ops.html 

1200 baud telemetry is just an occasional packet
every 10 or 60 seconds just like PCsat.  1200 bd
stations can simply feed their downlinks directly 
into the global APRS system like normal.  These 
will help update the LIVE PCSAT2 telemetry page
by G4DPZ at:

http://www.pcsat2.info/PCSat2Web/RealTime.jsp 

1200 baud capture files will not be requested to be
emailed unless there is an anomoly and we need 
some missing data.

9600 baud stations will see the special solar cell 
experiment data which is used to measure cell 
degradation over time.  We need the first data sets 
as a benchmark for future comparisons.  Having 
many ground stations capturing the data will  help 
assure a complete initial data set.

54 lines of 9600 bd data are transmitted as a beacon 
group once every 3 minutes 20 seconds consisting of 
11 one-sec data bursts of 5 lines spaced every 2 secs.  
The 5th byte of each line is human readable as a 
serial number starting with "A" through "Z", then 
"a" through "z" and then "0", and "1".

The "challenge" is due to the high UHF Doppler and
the burst nature.  You have to anticipate the Doppler 
to get a complete set since there is nothing to tune 
in until it has begun.

Volunteers who want to take on this challenge:

1) Please be sure to set your TNC and PC clock to
UTC within a second or so.  Be sure time-stamping
is ON.  Use Hyperterm or ALOGGER or any other
capture tool (ALOGGER format is preferred).

2) Use this file name convention with time stamp
and your callsign to save the file, and also use 
the same format for the subject line of the Email. 

    PC2_YYMMDD_HHMM_CALL.txt

3) Email to PC2 at grc.usna.gov 

Soon we will have a separate SATGATE server just
for collecting this data and a specialized version of
ALOGGER which can not only log, but also serve
as a simple IGate for feeding your serial port TNC
into the SATGATE server.

ALOGGER is available from: http://www.billdiaz.dynip.com/ 

TUNING DOPPLER:  Remember that at AOS the
UHF signal will be as much as 9 KHz high and at LOS
will be as much as 9 KHz low.  But at these times
the doppler is *changing* the least and this is
probably the best time to catch a complete file
without any tuning glitches.

In the middle of the pass, the Doppler rate of
change is the highest and although the signal
will be strongest, over the center 2 minutes
the doppler will shift as much as 8 KHz!  This
is why we expect to have to combine files 
from multiple users to get a complete set.

Computer tuning may not help, since the step-
transition during a tuning step may garble a
packet?

Also, all of our web pages will be down during
this ccritical time since our entire building will
be shut down for long planned electrical power
work.  Our command station will be operted via
an emergency generator and a single long
extension cord offering 15 amps.  So read these
web pages well prior to the event.

Good luck.
Bob Bruninga, WB4APR
USNA Satellite Lab