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[Discuss-gnuradio] Block & Specification Queries
From: |
Michael Hill |
Subject: |
[Discuss-gnuradio] Block & Specification Queries |
Date: |
Mon, 25 Jun 2012 21:29:01 +0930 |
I have a 5 questions that are probably relatively straightforward so I
thought it'd be easier to lump them all in together.
Some of these have
been touched on in some other disussion threads I found but I wanted to
clarify the answers..
To put things in
context, I am doing radar research and am looking at replicating simple signals
such as CW, Doppler Pulses, FMCW Chirps etc.
Thanks in advance,
I'm very new(ish) to alot of signal processing and even linux so its been a
steep learning curve for me!
**Amplitude
Parameter
The Amplitude
parameter affects the Amplitude dB output, but from what i've determined / read,
it is only linear up to a certain level.
E.g. I thought I
read somewhere that 1 should be considered the maximum digital amplitude
but (for example) that for the RFX1200 the maximum should be considered to be
0.2 before the dB amplitude increase as a factor of the amplitude parameter
starts to be come non-linear. Is this due to the fact that the maximum power
output is stated as being 200mW? E.g. Can I therefore correctly assume that for
the XCVR2450 that 0.1 should be the maximum value for the linear
region?
Also is the
amplitude (db) fft plot the idealised / theoretical power I
assume?
**Freq Modulation
Block.
This block has a
sensitivity parameter, but is this effectively just a tuneable parameter, e.g.
if I put in a 4 how does that differ from a 2 or a 1?
E.g. Does that
mean the frequency will be modulated to a frequency 1/4 of the original, as
opposed to 1/2 or 1/1?
Over what time
frame will this change take place? I'm aiming to create chrips using existing
blocks. I've read that feeding a saw tooth into a Freq Mod block is the best
option.. but i'd like to be able to control the time and compression
factor.. i guess the time is affected by the period time for my ramp, and
amplitude is my sensitivity but again.. what does this equate to? :/ I'm just
not sure.
**Bandwidth
The XCVR2450 has a
bandwidth of 33MHz according to the first link below, but according to the second.. it
says it can cover
Tx: 24, 36, 48 MHz; Rx 15, 19,
28, 36 MHz. I'm a bit confused by this
**Sampling
Rates
When running some
grc files via gnuradio companion with my USRP N210 (with a Basic Tx
Daughterboard),
I often
find that I get an output saying something to the effect
of
Target Sampling Rate
= 22Msps
Actual Sampling Rate
= 20Msps.
In fact when testing
through a bunch of sampling rates I find it almost selecting sampling to
rates such as 20Msps, to 25Msps or sometimes 33.333Msps.
What
impacts the selected sampling rate? E.g. is this a factor of the clocking
frequency of my computer, the USRP, both or something
else?
**Real time
Scheduling
I still can't seem
to get Real Time Scheduling going despite having added the
@usrp
- rtprio 50
to
/etc/security/limits.conf
(and also setting Real Time Scheduling to "on" in my top
block)
My computer is a
3GHz Quad Core, so i'm surprised I can't this isn't working
Would chaning
it to @usrp
- rtprio 99 make a
difference?
- [Discuss-gnuradio] Block & Specification Queries,
Michael Hill <=