ENIGMA 2000 Newsletter - Issue 33

March 2006
Articles, newsreports and Items of interest :enigma2000-owner@yahoogroups.com

A software defined radio for numbers or oddities

By CapitaneX

And now an interesting SDR receiver from ENIGMA 2000 Member ‘CapitaneX’ :

1. The Hardware

I am familiar with radio and specially with ham radio for about 15 years. But never I had a better receiver-system than today.

The good news are, that, if you have a good computer, or specially a good soundcard, the costs for the receiver are about 20,- Eur's.

That is not to much.

The main advantage for use all this for finding Numbers and Oddities is, that you can easily separate them from Utility and Broadcast Stations.

In the best conditions you will have a 96 kHz wide view at the spectrum.

At first, the design of the receiver is not from me, but i put this all together to a complete system.

softradio electronic design
The original design is from Edson Pereira, PU1JTE.

Please see: http://appr.org.br/qrpbr/resource.php?rid=9

As may you notice, this is not so complicated. There are only three integrated circuits and a few resistors and capacitors.

The bad news are, all of the integrated circuits are SMTs. But there are some articles on the web, that will show you, that it is not that complicated to solder SMTs, as you may think. For Soldering SMT Details, see for example here:
http://www.elexs.de/smd.htm

But this is only the quadrature sampling detector circuit. As a local oscillator I added AD9850 DDS-Circuit which I built from the design of the AMQRP DDS-daughtercard.

Please see here:
http://www.njqrp.org/dds/index.html

The AD9850 is controlled via a simple little C-Program, which I have rewritten for me.

Specially for Linux exists a Environment which gives a feeling, like sitting in front of a expensive DSP-Receiver.

For Linux Details please see here:

Java-GUI from John Melton, G0ORX/N6LYT
http://microsat.homelinux.org/dttsp/
Dttsp-Shell from Edson Pereira, PU1JTE
http://ewp.homelinux.net/dttsp-shell/

There are many theoretical articles about quadrature receivers, so I will describe here the usage in Monitoring the Shortwave. For general SDR Infos please look here:
http://www.arrl.org/tis/info/sdr.html

It is important to read the base articles from Gerald Youngblood (AC5OG) over the “Software defined Radio for the Masses”. You will find four article at the Link from above at ARRL-Headquarters.

In an Software Defined Radio (SDR) the main digital signal processing is done by the Sound card. You can use every Sound card, but later you will notice, that the cheaper Sound cards have a very bad noise level and are limited to a receiver bandwidth of for example 48 kHz.

I use the M-Audio Delta 2496 Audiophile Sound card. This Sound card is able to process up to 96 kHz of full bandwidth. This Sound card costs about 88,- Eros ( http://www.m-audio.com ).

2. Some Software Examples / Screenshots

a) Flex-Radio PowerSDR

http://www.flex-radio.com/downloads.htm#PowerSDR

Open Source Software by Flex-Radio

Power SDR screenshot
Screenshot taken from Software PowerSDR

In this example you see the beacon “D”. Lower part of the Picture with full bandwidth and in the upper part with selected signal and filter set. This is done with one simple Mouseclick.

b) Rocky

http://www.dxatlas.com/rocky/

Freeware by Alex VE3NEA

Please follow the link to see the System Requirements

Rocky screenshot

Screenshot taken from Rocky
http://www.dxatlas.com/rocky

In this example you see the full bandtwidth of 96 kHz at about 6.000 MHz. You see some Broadcast (A3E) and two DRM-Broadcaststations in the Middle of the Picture. In the Spaces between you can often find Number Stations.

This Picture shows the 40-Meter Ham Radio Band. You see at the left, the CW-Portion, in the Middle some PSK-Stations and at the right the J3E-Stations (lower-sideband).

The disadvantage is that this system described, is only able to go up to 7,5 MHz, because the QSD-Circuit needs a four times higher local oscillator.

The next version of my SDR will be the Softrock-V5 which is able to receive directly on the frequency, so that I will be able to cover the full shortwave bands.

For Details of the Softrock-Receiver see here:

In the next Newsletter I will describe to use all this with Linux.

Stop press

I just found this really good website of Building the Softrock-Receiver together with a DDS-Controller. He described lots of Bandpassfilters to use the System from 500 kHz to 22 MHz.
http://www.geocities.jp/qrper72/srv5spurious.html

73 for now CapitaneX