For our talk on 24th February, Walter Blanchard, G3JKV introduced members to the Weak Signal Propagation Reporter system. This uses a clever suite of software which encodes the message to be transmitted, and monitors and decodes other WSPR stations that you can hear, during precisely timed periods with a 2 second cycle time. The monitored signals are decoded and uploaded to a web site which publishes the results in tabular form for further analysing and mapping. In effect it is a world-wide beacon network additional to the traditional beacons (-which are not comprehensibly monitored and tend to have larger power than "weak")
This new digital system is already used by 2 or 3 CARC members (including G3YSX, G4FYY and 2E0MZB) and I hope they will correct and expand on my notes taken during the talk.
In WSPR "weak" means output from the TSCVR of 5 or less Watts and the software can decode signals received with Signal to Noise (S/N) ratio as low as -28dB. This is about 500 times "better" at decoding than the human ear listening to voice on SSB. If like me you find dBs hard to appreciate the WSPR website provides tables of power in Watts and dB equivalents.
The software has been written by Joe Taylor K1JT who is a physics professor at Princeton University, New Jersey, and who with his colleague Russell Hulse won the 1993 Nobel Prize in Physics. Professor Taylor's group continues to explore problems in astrophysics and gravitational physics by means of radio-wavelength studies of pulsars. Among recent highlights are the discovery of many new pulsars, including millisecond and binary pulsars.
In operation the PC generates the encoded signal and switches the radio to transmit at precisely the right time i.e. at the being of each even minute. The PC needs to know precisely the correct time and this is obtained from a time server on the web e.g.
dimension 4 at
http://www.thinkman.com. The last 6 seconds of the two minute cycle are silent. The PC can run Linux, Windows etc. and a processor speed of at least 1.5GHz is suggested by K1JT, although Walter suggested that 500MHz is satisfactory.
InterconnectionInterconnect between the PC and TSCVR is identical to that used for PSK , RTTY etc.
The connection of the PC serial port and the radios Push to Talk (PTT) is often made to part of the accessory port of the TSCVR. This can include optical isolation and 1A power transistor to handle the current needed by some TSCVRs to switch to Transmit. To carry the audio between the PC sound card and the TSCVR an isolating transformer will prevent the PC's dc voltage on the sound card reaching the TSCVR and vice versa.
There is a wealth of designs and information about PC to TSVCR connection techniques at provided by W5BBR (Google says that there should be a www.w5bbr.com/soundbd.html site, but this did not seem to be up when the editor looked for it. However the material can also be found at
http://www.cqham.ru/soundint.htm). The latest version of the software allows interconnection by CAT system, which additionally ensures the frequency set in software matches the TSCVR setting.
The Encoded Signal The transmitted signal contains information using Frequency Shift keying (FSK) at the low shift value of only 6 Hertz(Hz). The encoded transmission includes; sender's callsign, Tx location and Power level in dB. As the shift is so small it can not be heard by the average listener and the transmitted signal sounds like a continuous 1500 Hz tone. When listening typically there is ?beat? occurring between signals and "woof-woof" sound is heard. The signal is contained in a 200Hz Pass Band.
WSPR signals heard are decoded by the PC and can then be upload to the web at
www.wsprnet.org. There are millions of monitored signals on the site and data can be selected for further analysis. To register with the site you need your Maidenhead locator
http://www.levinecentral.com/ham/grid_square.php will give latitude and longitude plus Maidenhead locator directly from your callsign using data from QRZ.com.
Having downloaded the WSPR software, to get started try the 30m band as this has many monitored calls listed in the webpage, where distances and azimuth angles are tabulated. Once monitoring is working and your PC is decoding some of the results you can see on the web, you can consider transmitting. Walter drew our attention to the following points
*Correct UTC time (from internet atomic clock)
*Correct dial and transmit frequency remembering that changing freq on rig does not alter the data set on the PC
*Start with Transmit to Receive ratio set at 20%
*Choose the correct frequency band on the menu bar
*Check Rx noise ? needs to be 1dB plus and minus 10 dB tolerance
*Select USB mode
*Use TSCVR with frequency stability within 2Hz at 28MHz or you may need to add the manufacturer's "high stability Oscillator" cost about £50.
What is it good for? Well there is all the data to analyse in any way you wish. The effectiveness of aerial types, locations, mounting etc. and TSCVR type and power can be monitored by adding switching to change the equipment automatically during the 6 second silent period.
Map of monitored calls 
More information Try
www.g4ilo.com/wspr.html This is a clear comprehensive explanation and I suggest is essential reading. Also search for
wspr in
www.youtube.com to see wspr in pictures!
Further Links Steve Nichols G0KYA, RSGB Propagation Studies Committee
www.qsl.net/g0kyaWalter Blanchard email wb@g3jkv.co.uk
By Ted Aston G7OBF
