Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
On Thu, Jul 17, 2014 at 10:15 AM, [email protected] wrote:
My application is currently using an rtl_sdr (FC0013).
I get the best results when I use the built-in AGC option. However, there
are a couple of corner conditions where their AGC is not desirable. My
signal levels very pretty wildly from barely above the noise floor to just
about saturating the input with no gain.
Not surprising. You don’t have a huge dynamic range with those dongles.
When I set the gain on the rtl_sdr to nominal and put in an AGC2 block, I
found that resulting SNR was significantly worse than the builtin AGC of
the rtl_sdr. I limited the max gain, but I still seemed to lose most of my
signal as the noise floor rises significantly.
Again, not surprising. The AGC blocks in GNU Radio are a bit of a
misnomer.
They don’t really adjust the gain, they adjust a digital scaling factor.
So
you’re just multiplying the signal and noise together. These blocks
really
just make sure your signals come in scaled around where you want them,
but
don’t do anything with real hardware gain.
You definitely want to set the gain of the receiver to best maximize
your
SNR. But you’re always going to have the dynamic range issue, often
called
the near-far problem in some application spaces.
specific channel.
Does anyone have a good example or suggestion of an AGC usage to place
right after the source?Thank you guys! This forum, the gnuradio and its collateral project, and
the community have been awesome!
Thanks!
Jim
You’ve stumbled onto a pretty difficult problem that tends to be very
application-specific and hardware-specific. Hope I’ve given enough
basics
above to help you tweak your app.
Tom