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Re: [Discuss-gnuradio] DBPSK and Carrier Suppressed or Not?
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] DBPSK and Carrier Suppressed or Not? |
Date: |
Wed, 18 Mar 2009 13:30:04 -0700 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Wed, Mar 18, 2009 at 02:55:41PM -0400, w w wrote:
> I'm putting together a DBPSK Tx and Rx and running into problems when the
> modulated signal hits the USRP. When I receive the signal on the USRP
> there's a very pronouced carrier....I've confirmed with a spectrum analyser
> that the signal on the FFT is the one that I'm recieving. It seems to me
> that the sidebands should be close to the highest amplitute and the carrier
> should be suppressed.....is this correct? Shouldn't the output of the DPSK
> modulator FFT plot look very similar to the FFT plot on the RX side of the
> usrp? I'm modeling the block connections after the benchmark samples in
> the digital example section. I put a channel filter inline with the usrp
> and the dpsk demod block just like the example.....do I need to put more
> filtering in place to suppress the carrier? If so, do you have any
> examples?
>
> If I take the output of the modulator and go directly to the demod thru the
> channel filter, data flows just fine(bypassing the usrp).
>
> I'm only using one usrp and taking the output of the TX via coax and going
> into the RX side...that shouldn't make a difference should it?
>
> Any thoughts?
>
> Cheers,
> Jody
Before writing your own, did you take a look at the implementation of
dbpsk that's already in the tree?
See the -m dbpsk option below
$ ./benchmark_tx.py --help
Usage: benchmark_tx.py [options]
Options:
-h, --help show this help message and exit
-m MODULATION, --modulation=MODULATION
Select modulation from: cpm, d8psk, qam8, dbpsk,
dqpsk, gmsk [default=gmsk]
-s SIZE, --size=SIZE set packet size [default=1500]
-M MEGABYTES, --megabytes=MEGABYTES
set megabytes to transmit [default=1.0]
--discontinuous enable discontinous transmission (bursts of 5
packets)
--from-file=FROM_FILE
use file for packet contents
-f FREQ, --freq=FREQ set Tx and/or Rx frequency to FREQ [default=none]
-r BITRATE, --bitrate=BITRATE
specify bitrate. samples-per-symbol and
interp/decim
will be derived.
-w WHICH, --which=WHICH
select USRP board [default=0]
-T TX_SUBDEV_SPEC, --tx-subdev-spec=TX_SUBDEV_SPEC
select USRP Tx side A or B
--tx-amplitude=AMPL set transmitter digital amplitude: 0 <= AMPL < 32768
[default=12000]
-v, --verbose
Expert:
-S SAMPLES_PER_SYMBOL, --samples-per-symbol=SAMPLES_PER_SYMBOL
set samples/symbol [default=none]
--tx-freq=FREQ set transmit frequency to FREQ [default=none]
-i INTERP, --interp=INTERP
set fpga interpolation rate to INTERP [default=none]
--log Log all parts of flow graph to file (CAUTION: lots
of
data)
--use-whitener-offset
make sequential packets use different whitening
--excess-bw=EXCESS_BW
set RRC excess bandwith factor [default=0.35] (PSK)
--no-gray-code disable gray coding on modulated bits (PSK)
--bt=BT set bandwidth-time product [default=0.35] (GMSK)
-B FUSB_BLOCK_SIZE, --fusb-block-size=FUSB_BLOCK_SIZE
specify fast usb block size [default=0]
-N FUSB_NBLOCKS, --fusb-nblocks=FUSB_NBLOCKS
specify number of fast usb blocks [default=0]