This note sets out an initial plan of campaign for activities by the Anglian VLF group, and its Radio Amateur and other associates, after the granting of amateur LF licence permits. This strategy is not intended to be over-detailed. Specific details will be worked out later. A number of possible experiments are detailed in an Appendix.
The essential strategy is to perform some simple, robust activities aimed at establishing an initial and useful LF presence. A small network of low-power LF beacon stations gives a framework for:
Two transmitter sites, tentatively one in Suffolk and one in Leeds, would make a good basis for comparative experiments. The table below records some instant possibilities, there are certainly others.
|Leeds (1)||The University of Leeds would be a possibility. It has a large clear area within the town where a reasonable amount of aerial might be deployed. There would be certain EMC considerations to be looked at. Such a beacon could perhaps be run in conjunction with official University activities.|
|Suffolk (1)||John Rabson has a house in a rural village. The back garden is not over-large, but there is the possibility of negotiating access over farming land behind the house.|
|Suffolk (2)||A large industrial site in Suffolk has possibilities, but there would be EMC considerations. Securing permission to operate would require careful negotiation.|
|Suffolk(3)||A former extensive operational site, dependent on its new owner.|
The transmitter equipment would be as simple (and low-cost) as possible. It may prove possible to design and build a standard beacon transmitter based around some robust and cheap technology, perhaps using cheap FETs or power amplifier modules for the PA stage.
The initial beacons would be of low ambition and elaboration, and may be described as follows:
|Antenna||Site-specific, but probably electrically short, loaded and therefore of high Q for maximum radiation efficiency. (High Q implies low bandwidth.)|
|Frequency||The transmit frequency would be crystal controlled to a high stability.|
|Modulation||Low rate binary data, probably with a fixed pattern. The beacon would also require a statutory Morse identification. There might be periods of unmodulated carrier.|
|Operation||Subject to licencing conditions the beacons could be designed for unattended operation; this would require a (possibly procedural) panic button.|
|Parameter logging||Optional logging of parameters such as transmitter output power, feed current, temperature etc. would be possible using external logging equipment.|
|RF Power||Approximately 10W RF fed to the antenna, to permit simple construction, low power requirement and to minimise EMC problems.|
|Polarisation||Dependent on local conditions at the site chosen: horizontal, vertical or mixed.|
The internal and external co-ordination arrangements for the group's activities need further thought.
The initial beacon network would provide direct practical experience in a frequency range which Radio Amateurs have been absent from, as transmitters, for very many years. The results from the experimental beacon network would be fed in to proposals for one- or two-way data transmission at LF, and of course for further experimental and beacon studies.
The proposed small beacon network would quickly allow the Anglian VLF group and other Radio Amateurs to get to grips with a number of interesting problems. The results of the experiments would provide practical guidance for further developments, and would provide a mechanism for experimenter and general listener participation.
The good work of the RSGB licence liaison committee would be seen to be capitalised on. The RA would feel that their not inconsiderable work had been taken up and run with. Other people would be encouraged to join in the fun.Robin Gape
Experiments which could be supported by the proposed beacon network include, but are certainly not limited to, the following outline study areas:
|Propagation studies||Checks of path loss between beacon and receiving stations, and comparisons with other stations; time based observations of path loss; ground wave versus sky wave.|
|LF receivers||The design, construction and operation of LF receiving equipment, including computer controlled systems.|
|LF communication systems||The design of systems designed for communications at LF, using equipment and resources sensibly available to Radio Amateurs.|
|Morse tests||Detecting low speed morse at distances of, say, 10 km and 100 km. Low speed data. Detecting 1 bit/s data at an error rate of 1 in 104 at distances of, say, 10 km and 100 km. Detecting 10 bit/s data at an error rate of 1 in 104 at distances of, say, 10 km and 100 km.|
|Polarisation studies||Comparison of horizontal and vertical polarisations.|
|Transmitting Antenna studies||Estimation of transmitting antenna parameters (polar diagram,radiation resistance, etc.) both directly and from received signal parameters.|
|EMC||Study of EMC problems, as these relate both to transmission and reception.|