Eric Blossom wrote:
Matt, Bob McGwier (N4HY) and I spent last week working on GNU Radio
face to face. We got an incredible amount of stuff done, and not much
sleep!
Below are some of the highlights:
---------- snip ----------------------
You left out why it was possible to work this hard for a week and get a
lot done. The Blossom family hospitality is second to none. I stayed
in one of the newest and most lavishly decked out casino's in Reno
(cheap, $50 a night!) and did not put one red cent into a single slot
machine. The only time I managed to even enter the casino, it was to
walk through to the diner! It was a busy week, but an extremely
valuable learning experience for me and I am very happy Matt and Eric
persevered in my training until I could see how to do things. For those
that do not understand how things work behind the scenes, it is a
remarkable piece of work. With Stephane's recent contributions of the
SSE/3DNOW based routines for filtering and the FFTW SSE based FFT
routines, this code is remarkably efficient and is truly beginning to
meet all of its great promise.
My apologies on the Kaiser window. I got trapped like everyone else
that does a quick search. They get the Numerical Recipes code (usually
without a single line of attribution) as I did. Go to Julius O. Smith's
CCRMA resampling treatise and you will find the entire rationale for
what was done here for the rational (integer up, integer down)
resampler. Smith's fractional resampler is also very neat but we did
not need it for the week since the Eric/Matt had already implemented a
"compromise" but very fast fractional resampler. From my observations,
and where we are using it, it is not much of a compromise and as I
said, it is very fast.
Matt and I started the Costas loop and we all detoured to the PLL
blocks. We can and should finish the Costas loop to enable a fancy DSB
detector, QPSK demodulator, etc.
In gnuradio-examples/python/usrp you will find usrp_wfm_rcv_pll.py.
The difference between it and usrp_wfm_rcv.py is the latter uses the
arctan demodulator and the new one uses the PLL demodulator. The PLL
design parameters probably need tweaking. Give it a try if you have the
tuner. To my ear, it sounds brighter, but your ear might hear
differently. Let us know. I thought it might be more expensive
computationally but if it is, it is not by much. Matt ran it on his
abacus, err uhhh, 1.8 GHz (constantly throttled back for thermal to
600 MHz) laptop.
We looked at the FlexRF board for 70 cm and as Eric mentioned, we used
it for the GMSK. Matt's abacus could not send faster than 756 kbps
without glitching so I am sure it will run at least 1 mbps on a
desktop. In looking at the FlexRF, we managed to do the necessary
adjustments to suppress the LO to an extraordinary (and entirely
unnecessary) and to suppress the image to > 30 dB. This will be fine
for the 70cm, 900, 1296, and 2304 bands. I have two transverters for
1296 and 2304 that do not have this level of suppression. Matt used a
quadrature mixer in a neat package and it works.
The other thing we discussed as Eric mentioned and still need to make
progress on is the modification to the bit file for the USRP and then
implement the code to enable the phased array code. The need to modify
the bit file and the discussion of the applications of this hardware and
software to the C to C band transponder for AMSAT=NA's Eagle spacecraft
mission kept us from attempting an implementation of the phased array code.
My apologies to Matt. We had great fun at his computer's expense though
it worked just fine. I brought my great laptop only to discover that it
has USB 1.1 and had to spend 3 days getting SUSE 10 set up to compile
and run GnuRadio to even find that out!
What else did we forget?
Bob
I'm sure I've left out something important!
This wouldn't have been possible without the enthusiastic efforts of
Bob and Matt! Thanks guys!
Eric
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