At 10:54 AM 5/1/2006, Rob Frohne wrote:
Hi Everyone,
I'm interested in getting back into the software defined radio area
again. The last thing I did was the R2-DSP, and it looks like there
have been some good strides made since then. It looks like the SDR-1000
is an open design, but I'm still looking for the schematic and possibly
source code of the control circuitry board.
Schematics are on the Flex-radio website (the QEX articles have the
schematics, and I think there is a separate file with just the schematics).
There's no processor on any of the boards.. the various latches are all
decoded from bits on the parallel printer interface. Take a look at
http://home.earthlink.net/~w6rmk/sdr1000/index.htm and follow the link to
either the pdf or gif version.
I'm also looking for the
source code and the description of the protocol used to communicate with
the DDS and relays (or possible micro-controller that controls them).
Can someone direct me to all that information?
All hardware latches.
The DDS protocol is just the standard AD9854 registers, in the datasheet.
I don't want to just purchase an SDR-1000, and play with the software; I
would like to play with the hardware a little more this time, than I did
with the R2-DSP. Analog Devices is sampling the AD9954 now, and it
looks possibly more attractive than the AD9854. First, it has 14 bits
on the D/A, and I think it should have lower phase noise; third, it
dissipates about 1/4 the power, which is really nice because the AD9854
some special requirements when it came to the circuit board design
because of the heat dissipation. Down sides are that you will need to
use two AD9954's or perhaps you could use a Johnson divider and drop 6
meters, and the supply voltage is 1.8 volts, and I suppose there may be
some issues with the serial programming instead of parallel and syncing
the two DDS devices.
The SDR1000 doesn't lend itself to hardware modifications of that
scale. However, you could probably build up a board with a couple 9954s
that you could connect up to the TRX of the SDR1000, after removing the 9854.
As you say, there are some subtleties on synchronizing the DDSes, and
that's something that the SDR1000 doesn't make easy. In my own work with 4
SDR1000s, I made use of the fact that once they're running, you can measure
the phase offset between them, and it will remain the same. You can then
either move the DDS phase offset register around to line them up, or take
it out in software processing of the I/Q streams. I did the latter.
What other things should I consider?
Are there better reference oscillators available now? Are there other
tweaks to the circuit that you would recommend?
The standard oscillator is pretty darn good in terms of phase noise, it's
just not stable over temperature. You could feed in an external reference
(and accept the multiplication noise increase), or, calibrate against a
reference periodically.
Why has nobody made Gerber files available for the PC boards for the
SDR-1000?
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
