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Re: [Discuss-gnuradio] AGC loop
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] AGC loop |
Date: |
Wed, 20 Sep 2006 22:33:48 -0700 |
User-agent: |
Mutt/1.5.9i |
On Tue, Sep 19, 2006 at 01:36:55PM -0400, Robert W McGwier wrote:
> Tom:
>
> A good agc has at least two time constants. One for attack and one for
> decay. Your attack is much too slow.
>
> tmp = (reference - sqrt(real(y)^2 + imag(y)^2));
> rate = rate1;
> if tmp > gain rate = rate2;
>
> gain += tmp*rate;
Shouldn't this read:
> if tmp > reference rate = rate2;
^^^^^^^^
> rate2 is decay (where gain needs to be increased) and rate1 is attack
> where gain needs to be decreased. rate1 > rate2 and rate1 must be fast
> enough that you do not clip and destroy the first bits of information in
> a packet. If the packet has some idles, or other announcement data,
> then you want to recover fast enough to recover receiver parameters such
> as clock and carrier in addition to gain.
>
> Since you are doing dsp and have data in buffers, you can do noncausal
> agc as well. I do sense of the required signal level three time
> constants ahead of the place I apply the actual gain where time constant
> is determined by the attack rate. This works spectacularly well in
> DttSP. In addition to this, we actually complicate things a bit more
> much to our advantage by having two tracks of agc. One where rapids
> peaks and impulses flatten the gain but they release quickly. The
> other is a slower agc channel. The gain is the min of the two gains.
> Again, from all indications of the users of the SDR-1000, this is a
> spectacular agc. We allow for thresholded agc which does decrease the
> dynamic range but this is subject to user preference. Where you are
> doing data, and not listening to it, you probably don't care about
> thresholding.
>
>
> Bob
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, (continued)
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, John Ackermann N8UR, 2006/09/18
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, Lee Patton, 2006/09/18
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, John Ackermann N8UR, 2006/09/18
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, Lee Patton, 2006/09/18
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, Bob McGwier, 2006/09/19
- [Discuss-gnuradio] AGC loop, Tom Rondeau, 2006/09/19
- Re: [Discuss-gnuradio] AGC loop, Brian Padalino, 2006/09/19
- Re: [Discuss-gnuradio] AGC loop, Bob McGwier, 2006/09/19
- RE: [Discuss-gnuradio] AGC loop, Tom Rondeau, 2006/09/19
- Re: [Discuss-gnuradio] AGC loop,
Eric Blossom <=
- Re: [Discuss-gnuradio] AGC loop, Bob McGwier, 2006/09/21
- Re: [Discuss-gnuradio] AGC loop, Robert McGwier, 2006/09/21
- Re: [Discuss-gnuradio] AGC loop, Eric Blossom, 2006/09/21
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, Lee Patton, 2006/09/19
- Re: [Discuss-gnuradio] Using DSP for precise zero crossing, measurement?, John Ackermann N8UR, 2006/09/19