Digital modes are making their mark on VHF and above through their ability to process very weak signals (tropo and EME), to make use of very short meteor bursts or cope with multi-path signals (Aurora). Examples of performance are as follows:

WSJT stands for Weak Signal communications by K1JT, Joe Taylor. Its FSK441 mode has been specifically designed for meteor scatter. It can use random meteors that are available throughout the year. It works best in the range 800 km to 1800 km where contacts on 144MHz can be completed with 100 watts and a single yagi in typically 40 minutes.

Download Program at: http://physics.princeton.edu/pulsar/K1JT/

Operating Procedures in VK: FSK441-Proc

Performance: WSJT – FSK441

WSJT’s JT65 mode has replaced the JT44 mode provided with earlier versions WSJT. It is designed for EME and works well on tropo scatter. It uses Forward Error Correction techniques to decode signals, even with heavy QSB, down to -24 dB below the noise in an SSB passband and by correlation against a data-base of known callsigns can decode down to -28 dB. Tuning is not critical as it will pick up and decode signals anywhere within 600 Hz of the correct frequency. It requires computer time to be within a few seconds for correct decoding.

Stations with 100 watts and a single 10 element yagi can work the 10 or so super stations around the World who have 16 yagis or more and also work medium sized four yagi stations when moon conditions are favorable and by taking advantage of ground gain. The mode is useful at UHF and is starting to be used more widely on 432 MHz for EME. Tests show that providing one has good stability (less than a 10 Hz drift over each 46 second TX period) it can also be used for 1296 MHz EME. On 432 MHz one can work the larger stations (8 or 16 yagis) with a single long yagi (8wl) and 100 watts and on 1296 MHz a pair of stations with 3 meter dishes can work each other with 100 watts.

Download Program at: http://physics.princeton.edu/pulsar/K1JT/

Operating Procedures in VK: JT65-Proc

In its faster forms (5xHell and 9xHell) Hellshreiber works well on meteor scatter on six metres. However, it is too slow for random meteors on two meters and has been superseded by FSK441. In its slower forms (1xHell to 1/8^th Hell) it works well on tropo scatter but cannot compete with JT65. Despite this it is a real time mode that allows one to see the effects of propagation and is well worth the experience.

The one area in which Hellshreiber holds its own is auroral propagation. The reason for this is that it in its slower forms (1xHell to 1/8^th Hell) it copes well with both the multi-path propagation and frequency spreading caused by auroral propagation. Experience has shown that it can produce a readable signal from auroral propagation in circumstances where the signal cannot be heard by ear.

Some overseas stations have been experimenting with slow Hellshrieber for microwave EME where it has the advantage over JT65 that it can cope with libration frequency spreading.

Download program at: http://xoomer.virgilio.it/aporcino/

Spectrogram and Spectran and Spectrum Lab are waterfall programs that show the audio frequency spectrum and can detect signals in very narrow bandwidths even though they are looking across a much wider bandwidth. Essentially this gives one the advantage of a very narrow receiver (say less than 1Hz) but with the ability to watch for a signal across the full SSB passband. They are particularly useful in looking for very weak signals from beacons.

Spectrogram works to a resolution (equivalent to receiver noise bandwidth) of 0.3 Hz whereas Spectran will work down to 0.02 Hz and Spectrum Lab down to less than a milli-Hz. Of course to use milli-Hz resolution one requires exceptional stability such as provided by GSP locking and it may take tens of minutes to detect a signal. Earlier versions of Spectrgram were available for free but the latest versions require payment of a fee. Spectrum Lab and Spectrum are both free. Spectrum Lab has the widest range of functions but can take some getting used to. Spectran is an easier program to get started and is a good starting point. The later versions of WSJT include a waterfall program called SpecJT which is optimized to work with FSK441 and JT65.

Download Programs at:

Waldis, VK1WJ and Graham, VK2GOM, have been experimenting with a number of HF digital modes that have advantages where the QSB and the rate of change of Doppler is too fast for modes like JT65 and yet the weak signal performance of these modes allows contacts that are not possible on SSB. They seem to be useful for using backscatter from aircraft where the aircraft is not in line between the two stations. In such situations the tropo-scatter signal and the weak aircraft scattered signal often interfere causing very rapid QSB. Information on these modes can be found at the web site operated by Waldis at:

The requirements to run all of the above modes are:

An SSB transceiver and antenna

A PC with around 300 MHz Pentium or better and Windows 95 or above

An interface such as those widely used for PSK31: for example see article by Alan Gibbs VK6PG in Amateur Radio, March 2000, page 36.

Software that can be downloaded from the Web as above.

For the full bandplan refer to the following WIA site:

http://www.wia.org.au/bandplans/

The key elements for terrestrial use of the digital modes are:

The first frequency is the focus frequency and the second is an alternate. A similar pattern applies on all higher bands eg 432.225 for JT65.

At this stage there is no specific band plan for JT64 EME activity, however activity seems to be concentrated between 144.110 and 144.160 MHz on 2 meters. On 70 cm and 23 cm there is a trend to concentrate JT65 EME activity between 432.065 and 432.085 MHz and between 1296.065 to 1296.085 MHz.