AMRAD SDR & DSP Projects

This page supports both SDR and DSP work.




I replaced the original program-once 76.8MHz master oscillator with a custom Silicon Laboratories SI570, programmed for 76.8MHz. The new oscillator dramatically reduced the phase-noise related artifacts when stronger signals hit the Charleston Receiver board. This SI570 can be ordered directly from SI Labs, at a cost of about $13 each, but I recommend group buys. The SI Labs part number is: 570CAC000729DG. In order to have access to the extra I2C program pins (not absolutely required), I placed my SI570 on top of four zero-ohm SMT resistors, that act as spacers between the board and the SI570 itself.


Rob Bowers and Frank Gentges have built a Live-DVD that allows a computer to boot right into Ubuntu 10.04 and X. One of the two icons on the X desktop will load and execute Quisk for the Charleston SDR Receiver. This greatly simplifies demos and quick tests of computers for compatibility.


Quisk running on Charleston Receiver

  • AMRAD is working with the Charleston SDR board, developed by Dr. John Schwacke. An article describing this board was in the Jul-Aug 2009 AMRAD Newsletter. Also, see the Charleston SDR page for more information, including the newly-added Quisk for Linux as modified for the Charleston Receiver. This info is in the MIDDLE of the page.


I have added the text file for building the Charleston SDR version of Quisk 3.4.8 on Ubuntu 10.04.1. It is modified to add instructions to fix the broken wx-gtk link caused by a change in the latest Ubuntu. The file is:charleston build.txt


If you prefer, James Ahlstrom has given us permission to make available a single tarball of his Quisk 3.4.8 code, along with the Charleston modifications. It is: quisk-3.4.8 chas.tar.gz, and was added here on August 21, 2010 (and updated October 2010 to fix it with Ubuntu 10.04.1). To use this, simply download the tarball (probably to your home directory), uncompress it, change to the quisk-3.4.8 directory, and run "make". It should automatically compile the Charleston stuff as well as Quisk. You can then view/print the file charleston_build.txt file (in the quisk-3.4.8/charleston directory) for notes on dependencies and the rest of the requirements necessary to get Quisk for Charleston running.


James Ahlstrom has released a new version of Quisk (3.4.8), which has a number of improvements, including adjustable decimation rate (on the config menu). Jim's source (for Linux) is available at:, then do a search for "quisk".

Terry has modified the Charleston SDR Receiver support code to take advantage of Jim's additions. A tarball if the charleston directory is here:charleston-1.0.tar.gz . Once you download the tarball and unzip it, move all the files into a directory called charleston, inside your quisk-3.4.8 directory. You will then need to compile the quisk directory (type "make" while in that directory), then cd to the ./charleston directory, and run "make" again. NOTE: The file charleston-1.0.tar.gz was updated on Aug. 10, 2010 to correct a typo in the install instructions. Discard any previous versions.

Inside the /charleston directory are a couple of (hopefully) helpful files on how to get the proper libraries and build Charleston support, and a folder with mods to the file to add an audio filter shadow to the display.


We assembled a group of AMRAD members on a Saturday and we built Charleston receivers. We started by putting solder paste on the PCB using the stencil. Each builder built one or more PCBs by placing the parts on the boards. We left off the connectors, the LPF and transformer.

The boards were placed in a toaster oven. We tried to use visual inspection to tell when the solder paste was melted and while this worked, we ended up using the techFX reflow controller from which makes a professional reflow oven out of a simple toaster oven.

Then the connectors, LPF and transformer were added using a small tip soldering iron and the board was tested for power draw. It was not at all unusual to find pins on the fine pitch parts with a solder bridge to clean out. Sometimes one or more pins were not soldered down to the PCB. With a power check the final bridges fixed, most boards came up and worked. We want to pass on our knowledge to others on the group build. For one thing, it sure is more efficient than building just one receiver. We find we have fun and make acquaintances who will be working with their receiver.

Download and Follow the Read Me First File here.ReadMe1stV2.pdf

Block Diagram


To understand the receiver, first go to and search on the part number AFEDRI8201 and get the data sheet.

Then we have some information on the CIC Filter you can download. CICI.pdf cic1.pdf

CIC Understanding.pdf CIC Understanding..pdf

We checked new boards with our Power Test Fixture made out of an old floppy disk cable.



Here is more information and you can download the CD ISO image of our Quick Start CD V2.0 image here.


The CD includes some pictures of all the fun people were having. AMRAD members will get more info than the material we present here on-line. We are putting together information on writing design code for the Charleston receiver. That is a huge area to be explored.

March 2010 SDR Exciter news:

Terry has designed a companion exciter to the Charleston SDR Receiver. The design uses the Analog Devices AD9744 D/A converter, similar to both the openHPSDR Penelope board, and the James Ahlstrom exciter. An article describing the exciter appeared in the Sep-Oct 2009 AMRAD Newsletter.

AMRAD is looking for software and FPGA experts to help with both the Charleston SDR Receiver and the companion exciter. Windows or Linux platforms are of interest. Both projects use a Digilent Nexys2 500k FPGA board, which has a Xilinx Spartan 3E FPGA on it. More details can be provided.

Frank Gentges has organized one "run" of 20 Charleston SDR Receiver boards, all of which are running. A second run has been done. We have accumulated a lot of experience and it is presented in the Group Build page.

AMRAD has been interested in Software Defined Radio (SDR) since it became of practical application within amateur radio. We were fortunate to have a talk by "the Godfather of the Software Radio", Joseph Mitola III. He authored and co-authored several classic books on the subject.

(note: the following four items are not yet built/completed)

Some of AMRAD's recent and current activities are described beginning on the SDR Specific page.

SDR-related hardware information starts at: sdrhwinfo

SDR-related software information is available at: sdrswinfo

Miscellaneous SDR links: sdrlinks

Terry Fox, WB4JFI, is quite active in SDR experimentation, as described here: sdrwb4jfiovw

Frank Gentges, K0BRA, has constructed an SDR demonstration display, to use as a demo and recruiting tool at hamfests. A picture of a recent demo(SDR-IQ & Mini-VNA): SDR-IQ & MiniVNA demo

Some SDR background information can be found here: sdrbackground

A simple example of a Software Defined Radio (SDR) using only normal computer hardware including the sound card, to receive SAQ and other VLF (0-22kHz) signals han be found here: Johan SM6LKM SAQ SDR Receiver. This receiver implements a complete phasing receiver for VLF in C++. Source code and project description is also available, and a good place to study SDR and DSP techniques.

Here are some David Brainerd (WB6DHW) DDS/PIC/QSD boards:

Brainerd QSD


AMRAD has been actively involved with Digital Signal Processing for many years. Originally, we used the Motorola 56000EVM board, and various TI DSP evaluation boards.

As PC computing power has increased, the use of special-purpose DSP CPUs and boards has diminished significantly. Today, many DSP functions are being handled by the normal PC or MAC (desktops or laptops).

AMRAD (and Terry) still have some of the special-purpose DSP hardware and software, but is VERY RARELY used.

Some related DSP information (temporarily shown):

DOS-based spectrum analyzer: dosanalyzer

SM5BSZ hardware/software: sm5bsz

Additional information will appear here soon.

There is another important source, and that is YOU, dear web surfer, who may have the most exciting news yet! If so, send email to the webmaster (click on link at the bottom of the page) pronto.

Mel Seyle (W4MEL) and Terry Fox (WB4JFI) mods to Edson's sdr_shell (Linux):


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