Talks presented in 2024
SWR Bridge - 18.9.2024
The presentation from Pavol, 2E0LCP, included an overview of the theory behind standing wave properties and their amplitude measurement.
We travelled back in time to a seminal paper published by Warren Bruene from Collins Radio Corporation in 1956 and get acquainted with his work and principal schema for the circuit. We analysed a theoretical circuit. Furthermore, we also looked at the practical experience of building the device and demonstrating its function.
WSPR Beacon - 30.10.2024
The October talk was given by Barrie, G8GTV, on the subject of WSPR (Weak Signal Propogation Reporter).
He described the application function and how WSPR can be used for checking propogation conditions and aerial efficiency and directivity. It was also interesting to see how very low power signals can be received globally. The construction of a WSPR beacon was described together with the protocols and an offer to help anyone who might wish to construct a beacon for themselves. The talk ended with his beacon in transmission mode and an almost instantaneous reception report from Finland. The transmitted power was 200mW.
Talks presented in 2025
GB3SW repeater updated and working - 29.01.2025
Dave, G6XUV and Jason, the principal actors behind GB3SW repeater group, gave a talk about the update of the repeater.
The repeater was originally located in Honiton, and managed by Alec Duffield (Silent Key). Since 1995, Dave Lee, took the maintenance over.
The repeater group is an independent body, not affiliated to SARS, however some members of the group are also members of SARS. Since 1995, the repeater was hosted in Norman Lockyer Observatory, until 2014. The repeater was then moved to Lower Sweetcombe Farm, location IO80JR.
Last year, the repeater group was faced with a deteriorating performance of the existing hardware kit. A decision was made, to update the repeater. By some lucky coincidence, YAESU UK, offered a long term loan on the new hardware for repeater. Thanks to their technical director for stepping in!
Apart from existing VHF analogue capabilities, the repeater is planned to be updated with DMR and C4FM.
Jason explained technical challenges, which are providing separation of send/receive frequencies, which are just 600 kHz apart. To meet the requirements, a duplexer is used. This duplexer has very sharp transfer characteristics, allowing about 60 - 100 dBm of separation between signals. The duplexer consists of4 barrels with tunable resonators. In addition, a circulator is used to help to separate the signals, as there is only one antenna used in the repeater.
The repeater was switched on again on 29th of December 2024. It quickly became an asset for the regional radio amateur community. The presentation clearly demonstrated that rebuilding the repeater was a gargantuan task. Technical problems, starting from refurbishing of steel cabinet, adding heat isolation, and being able to tune resonators inside the cabinet easily, have demonstrated the motivation and enthusiasm of the repeater group. Seeing is believing, and all the fancy equipment used to get the job done, just evidences motivation and skills of the repeater group.
On behalf of the society, thank you all, providing such a great asset and a fascinating presentation.
The History of Honey - from Caveman to Touch&Pay - 26.02.2025
Stewart, HA5RV, talked about money.
The History of Money - A brief exploration of the evolution of money, from the self-sufficiency of autarky to the rise of fiat currency, examining how it works and some strengths and weaknesses of each system and why they ultimately gave way to new forms of exchange.
The presentation first defined money as a store of value and means of exchange. Also, several key characteristics of money were listed - such as scarcity, the ability to store the value, possibility of division, the equality and division to smaller units. A few initial slides gave a good handle on what money is, and how they were created, and why they were created.
Some typical examples of ancient currency and inflation were mentioned. The typical example is an ancient Rome, where two types of coins were introduced, one with a lower intrinsic value. In the end, the public did not want to use the new coin, and the old coin kept in circulation.
Several other inflationary scenarios were explained, based on the fact that in 1971, the value of USD was separated from gold. This process introduces fiat currency, that money became ubiquitous, plentiful, and with no intrinsic value.
The value of the money is represented by the trust in the governments and central banks issuing the money.
Finally, the presentation explained compound interest, its mathematical formula, and effects.
On behalf of the society, thanks to Stewart for sharing his professional knowledge on the subject.
Personally, it is clear that large-scale investing is a debatable subject, as the value to be produced physically will not exist. I will ask Stewart for some of his slides to be linked to this summary.
A brief history of communication usign light. 02.04.2025
Presented by Diane, M6YWX.
Diane first explained the speed of light measurement by Galileo. Galileo and his assistant were standing on the hills' tops, with a known distance between them. However, the light was too fast to measure the delay.
Danish astronomer Olaus Roemer, measured the speed of light, based on observations of the eclipses of the moons of Jupiter.
The speed of light as we know it today is 300 000 000 m/s - 3x108 m/s.
Some typical examples of ancient currency and inflation were mentioned. The typical example is an ancient Rome, where two types of coins were introduced, one with a lower intrinsic value. In the end, the public did not want to use the new coin, and the old coin kept in circulation.
Ancient Greeks used hydraulic telegraph, mounted on the hills' tops to transmit messages. It was as early as the 4th century BC.
It consisted of a container filled with water and a vertical rod floating within. The rod was inscribed with various messages along its height. When the remote torch signal was received, water from the container was slowly drained until the signalling torch went out again. Through the position of the inscribed rod, the water level could be correlated with a specific message.
Similar principle was used by Chappe brothers in France, in the late 18th century. They erected a network of semaphore towers in France for military communications. The movable wooden arms connected by crossbar allowed to display 196 symbols. The symbols were transmitted from tower to tower.
Finally, more modern means of communication were described.
- Aldis lamp
The Aldis lamp was invented in the 1860s by British Royal Navy Captain Arthur St. Vincent Aldis. The first Aldis lamp was a kerosene lamp with a convex lens and perforated shutters. With ideal conditions these lamps could send messages accurately up to about 20 miles in daylight, ship to ship.
- Lasers
- Lifi
Fully networked optical wireless technology that uses the spectrum of light instead of radio waves to exchange data.
