As you know, the SoftRock-40 is a small and low-cost 40-meter
"software defined radio" receiver that plugs into a computer
USB port and delivers I-Q audio signals to the computer's sound card.
It's a stellar performer with an MDS of about -128 dBm and killer
"PC front panel" ... The
PowerSDR Console program presents a virtual front panel that looks just
like the front of a real fancy (read: expensive) commercial transceiver
with lots of pushbuttons, controls and a graphical spectral display of
the received frequency.
But there are many different directions that users can take by
experimenting with the SoftRock's "quadrature sampling
detector" basic core. This page overviews some of those
experimental projects in progress.
Portable
SDR with the "SoftRock-908" ... George N2APB and Lyle KK7P
We have been experimenting with an integration of the SoftRock with the
Micro908 and a new "dual DDS" daughtercard. The DDS
driver of the Micro908 was modified to control the dual-DDS board (coming
soon from KK7P). This DDS2 card generates the individually- and
precisely-controlled local oscillators used with the quadrature sampling
detectors in the SOftRock, thus producing the IQ audio
representation of the received signal. Now, connect those two
audio streams into the DSPx Daughtercard contained within the Micro908,
add the appropriate demodulation software, and we'll have a standalone,
portable Software Defined Radio ... no PC required! Pretty cool
for that little Micro908 platform, eh? This
"SoftRock-908" SDR radio is one of the main applications for
which the Micro908 was envisioned back when designed and introduced
last year. And it all keeps on getting better and better!
.jpg)
New
KK7P “DDS2” card (card
on left) serving as an
extremely flexible and precise dual local
oscillator for a prototype of
the SoftRock-40 receiver (upper card), making multi-band operation
possible. This sub-assembly can be plugged into the AmQRP Micro908
motherboard in place of its current (single) DDS Daughtercard. With a
new software driver for this DDS2 card, the Micro908 rotary encoder and
LCD serve as the “front panel” for controlling the SoftRock-40
receiver operation anywhere on the 40m ham band.
DDS2+SoftRock
board in position
inside the Micro908
instrument. The Micro908’s user interface and built-in nature of the
DSP card (daughtercard in the lower right corner) make a standalone
Software Defined Radio quite possible. In this prototype, the SoftRock
audio signal cable is plugged into the input jack of the Micro908
enclosure (cable input at upper left of diagram), which then routes the
audio signals over to the DSPx Daughtercard on the motherboard.
“Using
a DDS Card to Drive the SoftRock-40” … Bill, KD5TFD
When I built my SoftRock-40, I wanted to perform some experiments and pair it up with a DDS Daughter Card from the AmQRP to give it more tuning range, so I replaced some of the components on the SoftRock-40 board with headers so I could tie-in the DDS signal from the daughtercard. Specifically, I replaced the Q1 pass transistor with a 78L05 5V regulator and did not populate R18 and R1. I also put headers in place of R2 that powers the crystal oscillator, and C8 that feeds the output of the oscillator to the comparator. I also mounted headers at R18 (for input power to the 78L05) and at C2 (shorted together for ground). In the basic daughtercard setup shown below, R2 and C8 are mounted on the daughter board so the receiver
functions, then I built a little daughter board where I mounted R2 and C8 so I could run the basic stock version of the SoftRock-40.
The
basic version works great. IQ amplitude and phase balance of the
down-converted signal looks good and is easily balanced using the
PowerSDR software. A modified version of PowerSDR tunes +/- 24 kHz using
the DttSP receive oscillator (http://dttsp.sourceforge.net).
I also looked at the IQ output of the board from 6.9 MHz to 7.2 MHz. The
amplitude and phase response look fairly linear in this range, so tuning
wider ranges should be quite workable when using 96 kHz and 192 kHz
sampling rate sound cards.
Using
an NJQRP DDS Daughtercard and an
Atmel AVR Butterfly controller card, I was able to create a VFO using KD1JV
software. I figured this would make a good LO to drive the
SoftRock-40, so I connected them all together using a carrier board from
ERCOS
Technology, with the result shown below.
SoftRock-40 (on right) being controlled by an AVR Butterfly card driving
an NJQRP DDS Daughtercard, thus replacing the fixed crystal oscillator
and allowing the SoftRock-40 to reach across the entire 40m ham band. [Note:
The square pcb SoftRock-40 board used in this experiment was an earlier
prototype.]
In
this lash up, the Butterfly and KD1JV's software is used to control the
NJQRP DDS Daughtercard. The output of the DDS card is fed via a 47 pF
cap to the SoftRock-40 through the header installed in place of C8. The
header at R2 is left open, disabling the oscillator on the SoftRock-40
board.
Results
of the breadboard are quite good. Using the DDS card to drive the QSD
allows the tuning range of the SoftRock-40 to be moved all over the
40-meter band.
Updates
to this experimentation can be found on my web page: www.ewjt.com/kd5tfd/sdr1k-notebook/sr40/sw.html
Other
Development Directions ... Tony Parks, KB9YIG
The SoftRock-40 represents a minimalist SDR design, meaning that it cannot compete with the designs of more complex software defined radios like the SDR-1000 from Flex-Radio. However the low-cost nature and sheer simplicity of the SoftRock-40 hardware, when combined with the incredible power provided through the PowerSDR software running on the PC, all work together to make the project an astounding value. The educational benefit gained by using these basic
circuits and the excitement of operating a receiver with this degree of performance cannot be overstated.
We may try adding a USB-based sound chip to provide a direct interface to
USB so it can be used with any computer with a USB port - no sound card required! For laptops, this is especially cool because most of them lack
a stereo ‘line in’ connector for the internal sound card.
We'd also like to try the SoftRock with some of the other SDR software currently available. We've already used the board with Alberto Di Bene's (I2PHD) SDRadio
(www.sdradio.org)
program with good results. Phil Covington (N8VB) is planning on doing a SoftRock-40 version of his PowerSDR-derived SharpDSP code. This can be found at
www.philcovington.com/SDR.html. A neat feature currently in Phil's code that will soon be available in PowerSDR is the capability to have multiple simultaneous receivers within the bandwidth sampled by the sound card. Since it is all just software, having multiple receivers within the swath of RF coming from the hardware is only a simple matter of software. You would just need to setup another software mixer, filtering and demodulation chain and you've got multiple receivers.
And the best part of all this is that most improvements made to the PC
software can work with the SoftRock-40!
