Haven't heard about WSPR yet? WSPR stands for Weak Signal Propagation Reporter. It is a very clever digital mode to explore the propagation conditions on all amateur bands. Joe Taylor, K1JT wrote the software for it and he did a terrific good job. When your transceiver is linked to a personal computer or laptop, the software generates a short digital code containing your call, the first four characters of your QTH locator and your output power level. The line output of your computer generates an 4-level FSK signal that modulates your transmitter. A transmission always starts exactly at the beginning of the even minutes of the UTC time and it takes about 110 seconds to transmit the data mentioned above together with sync and forward error correction bits. Other WSPR amateurs also have installed the WSPR software and are listening on the dedicated WSPR bands. Because the WSPR decoding software is very sophisticated, signals that are 25 dB below the noise level can be detected. Once correctly received, this data is sent via Internet to the WSPR server together with the call and location of the receiving station. The transmitting station can go to the server website (www.WSPRNET.ORG) and look on a map or in a table where his signals have been received. Amazing to discover you have been received on all continents with 1 Watt of RF power within 24 hours as is shown on the WSPR map above. And the nice thing about it: you can start the software and leave it running. All you have to do is to look at WSPRNET.org to see your progress. Also as a shortwave listener you can participate. Just use the software to receive WSPR signals and automatically upload them tot the WSPR server. there is a lot more to say about is but just go to http://physics.princeton.edu/pulsar/k1jt/wspr.html to learn more about this magnificent way of sending your signals around the globe.

 Starting with WSPR

Is it difficult to start with WSPR? Oh no! You just need a simple interface between your computer and the transceiver (or receiver).  About that later. Just download the WSPR software from the website mentioned above and follow the instructions for setting it up. But remember that the frequency calibration of your transceiver must be adequate to tune it to one of the 200 Hz wide WSPR bands on the amateur bands. Reasonable modern transceivers would not give any problems since they have accurate timebases. Another point is to have your computer clock running exactly on time (within one second or better). A simple way is to synchronise it by hand with a radio controlled clock. A better way is to use one of the automatic computer clock synchronizing tools wich can be found on the internet. The photograph of the WSPR screen shows the received WSPR signals in every 2-miute interval by horizontal traces. you can choose the percentage you wil be on the air yourself. And to make things easy: the screen tells you the exact frequency you have to tune your transceiver to in order to be right on the WSPR band. At the bottom of the screen, you will see the status of the software (waiting for the next 2 minute interval, receiving or transmitting) and the received noise level which must be kept around 0 dB for optimum results. 

The WSPR interface

If you already have a digimode interface you are ready to go! Otherwise, building such an interface is not difficult. The schematic shows my solution. At the bottom of the diagram you will see the audio interfacing between computer and transceiver. Audio transformers TR1 and TR2 are used to galvanically isolate the transceiver from the computer in order to avoid ground loops. With the two potmeters the modulation level and the audio input level for the computer can be controlled. You can use the line-in and line-output connectors of your computer or buy an external USB sound card. If you have to use the computer's microphone input, use the attenuated signal on J13. The transceiver's audio output and modulation input connections can be found on the Accessory connector. The only thing we still need is a transmitter-ON command signal to bring the transceiver in the transmitting mode when the WSPR software decides to start a new transmission. There is a simple way by detecting the presence of the modulating signal genrerated by the computer. Comparator U1 "sees" the incoming modulation signal and translates it in a series of negative going pulses at the output of T1. NAND gate U2a provides a time delay which keeps its output high during the time the modulation signal is present. U2b gives an additional delay to eliminate glitches in de output signal of U2a. MOSFET T1 acts as a switch that grounds the transceiver's TX-on line as long as the modulating signal is present. Most transceivers have this TX-on line available on the accessory socket. Voltage regulator U3 is available to provide a 8 V supply voltage from a 12 to 16 V source. In most cases either 8V or 12 V is available on the accessory socket. A pcb has been developed for our local radio amateurs society. It measures 5 x 3 cm and is still available, either without components or stuffed with the surface mount components at the bottom side. Also the audio transformers for this PCB are available as well as all other components if requested. The block diagram shows the external connections of the PCB and the connections to the 13-pin accessory connector of the ICOM IC7200 and IC7600 transceivers. Other transceivers may have a different connector type and pinning. A neat encapsulation with the two potmeters for audio and modulation is used to protect the interface against the avarage shack environment. If you are interested in obtaining the PCB and assembly instructions or a partially or fully assembled one, please contact me by email: This email address is being protected from spambots. You need JavaScript enabled to view it.. for further details.