[linux-dvb] scanning for symbol rate [re: zig-zag thread]

Jeremy Hall jhall at maoz.com
Mon Oct 1 15:53:44 CEST 2007


Hello,

Recently I've been writing a program that tries to guess the symbol rate of a carrier, assuming it is QPSK, and that the frequency is right.  It's pretty basic right now, it sets the fe parameters, waits a specific period of time, drains the events, then attempts to determine whether it has a lock or not.

so I originally told it to wait 5 seconds in the timeout, and in another window I ran dvbsnoop -s feinfo to determine what was goign on.  To my horror, I noticed the srate was varying.  I was incrementing srate by 1, and the driver was helping me.  This makes the scan take a _LONG_ time, because it is scanning the same symbol rate multiple times.

so if I assume the FEC is auto, and that spectral inversion is auto, what is the best method to use to hold the frequency constant and vary the symbol rate? Even if this method gets you off by one or two, you can figure it out manually, but trying to run dvbtune in a loop or writing a special program seems a bit difficult.  The program would be fine, but it takes several hours to find the symbol rate depending on how far off your guess is.

It's a stv0299.  how long does it take to lock a carrier, and can somebody describe what it does to 'help' you? Maybe in that I can actually let it help me in a useful way.

_J



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