Hi LRK,
Thanks for the reply! I thought so too, that this capture effect or
phase locking or limiting should come from the demodulator or clock
recovery block, but looking at the c++ files, I couldn't find anything
related to this. Did I miss something?
The receiver is connected as follows:
self.fmdemod = gr.quadrature_demod_cf(1)
self.freq_offset = gr.single_pole_iir_filter_ff(alpha)
self.sub = gr.sub_ff()
self.clock_recovery = gr.clock_recovery_mm_ff(omega,
gain_omega, mu, gain_mu,omega_relative_limit)
self.connect(self, self.fmdemod)
self.connect(self.fmdemod, (self.sub, 0))
self.connect(self.fmdemod, self.freq_offset, (self.sub, 1))
self.connect(self.sub, self.clock_recovery, self)
But looking at eigher
gr_clock_recovery_mm_ff.cc
http://gnuradio.sourcearchive.com/documentation/3.2.2.dfsg/gr__clock__recovery__mm__ff_8cc-source.html
or
gr.quadrature_demod_cf.cc
http://gnuradio.sourcearchive.com/documentation/3.2.2.dfsg/gr__quadrature__demod__cf_8cc-source.html
didn't help me... any suggestions?
In front of the demodulator is also the Low pass filter:
self.channel_filter = gr.fft_filter_ccc(sw_decim, chan_coeffs)
best regards, B
Quoting LRK <gr-u...@ovillatx.sytes.net>:
On Thu, Feb 23, 2012 at 03:31:03PM +0100, bjoe...@ee.ethz.ch wrote:
> This sounds more like an AGC effect. If the gain gets reduced a bit,
>the decoder may not see sync from the weaker jammer. FM or PSK receivers
>usually have very fast limiting rather than AGC. Fast limiting is what
>you want so you can receive all packets possible.
This sounds promissing...! But how would I access the settings from
the limiting mechanism or the AGC?
I'm using the XCVR2450 Daughterboard on the USRP1. I guess the AGC
should be somewhere on there,
The gain is set in the hardware but the 'automatic' should be in the
software. I think you said you combined the zigbee and tunnel.py.
I use the usrp_fft.py to look at the spectrum and adjust the gain
slider to be just above the point where the noise baseline starts going
up. Mine shows a setting about 34. Then I set my software receive gain
there. Obviously the code needs to be similar and I think the UHD code
may be a lot different.
Your receiver should not need automatic gain control since it should
be either fsk or psk. The demodulator should do the limiter part.
--
The computer is supposed to work for YOU, not the other way around.
LRK
gr-user . ovillatx.sytes.net
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