On 03/19/2011 11:06 AM, devin kelly wrote:
I've only started using the AGC block very recently. I started using
because I wanted some way to control the AGC. This makes me think of
the question, is the AGC on by default? That is, if I don't have an
AGC block will the AGC be doing anything? Also, in the first two or
three ICs in the WBX there is a digitally controlled attenuator and an
LNA, those are part of the AGC correct?
There is no automatic gain control in the WBX hardware. The step
attenuators are set when you set the hardware RF gain of the daughter-card.
The AGC block within Gnu Radio simply applies a multiplicative
coefficient to the data stream within Gnu Radio, based on smoothed
historical signal power estimates.
AGC is useful for certain types of signals, and not for others, which is
why there's no automatic AGC in the hardware. Now various
daughtercards have *manual* gain control, and you can certainly
implement AGC that's distributed between software and hardware,
but that's up to the software. In general, in SDR, you want the
hardware to implement (borrowing from X11 for a second here)
"mechanism, not policy". Consider precision RF measurement
applications, for example. You don't want the hardware implementing
an AGC policy of any kind. Just like you don't want the hardware
implementing "the one, true demodulation mode".
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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