Chelmsford Amateur Radio Society

CARS Meetings: Jan - March 2022

January Meeting
4-Jan-2022, 7.30-9pm
Online by Zoom
"Cheating at Maths Using Computers"
Damian Bevan G4WPO

Our first talk of the New Year was on Tuesday 4th January, where we welcomed back Damian Bevan G4WPO, for a talk on 'Cheating at Maths using computers'. However Damian said that a more serious title for this talk would be 'Using computers to solve mathematical problems'.

In 1936, in the 'age of electricity', Alan Turing presented his machine which he hypothesised was able to compute anything which is capable of being computed.

It turns out that around a century earlier, back in the 'age of steam', Charles Babbage and Lady Ada Lovelace had already been having similar thoughts about mechanical computing engines, designed to solve mathematical problems. In those days, human 'computors' were used to laboriously calculate and tabulate the solutions to maths problems ranging from trigs and logs, to astronomy, nautical tide tables, banking and insurance information etc. Another famous computor was Katherine Johnson who did maths for Nasa flights (see the film 'Hidden Figures')

The earliest algorithms arouse from Ancient Greeks such as Euclid. Early mechanical / electrical computers models could only do basic maths or a fixed problem (such as Enigma), whereas more general purposes machines gave more flexibility for programming

Damian gave examples of:-

Of course radio is built on maths/physics - inc for propagation, link budgets, EMF calcs, radio circuit design, digital modes and SDRs

Some programming tools that are good at maths are widely available. Python is great at general work, but there are free addons such as Numpy to expand its maths capability.

More specialist tools include Mathematica, Matlab, GNU-Octave, Mathcad, Maple, Julia and SageMath

Summarising, Damian commented that the mathematicians of yesteryear were geniuses, with vivid imaginations, but very limited by the tools available.

In contrast the modern world has been developed on the back of sophisticated maths and amazing computing power -with remarkable capability just in your smartphone/pocket; and with plenty of effort going into Software Defined Radios, CGI effects for gaming/films or virtual reality.

Our thanks again to Damian for his presentation and insights

February Meeting
Tue 1-Feb-2022, 7.30-9pm
Online by Zoom
"Royal Signals and Amateur Radio"
Geoff Budden G3WZP

The February talk was a great insight from Geoff Budden G3WZP into the Royal Signals Museum and its amateur radio outreach efforts

Historically, the Corps of Signals were formally created by royal warrant in June 1920. Provided you register to visit in advance, the Royal Signals Museum at Blandford Camp in Dorset, is a great walk through this history. It features a diverse range of interactive displays illustrating the science and technology of communications.

Founded in 1920, the Signals celebrated its centenary recently with special event call GB100RSM. Exhibits at the museum include Enigma, SOE and Suitcase radios, army radios and command vehicles and much more.

Geoff has also spent a lot of effort on a major project that has been supported by the RSGB, RCF (Radio Communication Foundation), Yaesu et al. The result is a custom-fitted out small trailer to take radio demos to schools and other outdoor events

So whether it’s the museum itself or one of their outreach events – well worth considering!

Geoff G3WZP – Museum Volunteer

The Royal Signals Museum

The Radio Outreach Trailer

G3YUE Inside

Useful links

March Meeting
1-Mar-2022, 7.30-9pm
Online by Zoom
"Digital Amateur TV"
Dave Crump G8GKQ

CARS were pleased to have leading developer and RadCom columnist Dave Crump give the very colourful February talk on the innovative world of Digital Amateur TV (DATV. This is real fastscan and has seen huge progress over the years. It has evolved from 405 lines and valves to take advantage of digital technologies so that high definition colour modes and more.

Until the 1990s the dominant mode was FM-ATV and needed such bandwidth it was largely confined to 23cm, where it is well supported by tv repeaters as well as on the 10 GHz band. Analogue ATV has long since gone from 70cm.

However the amateurs have made major strides by adapting digital modulation and codecs so its bandwidth has dropped substantially to the point it is now common on 437MHz, and 146MHz where it can achieve great distances, as well as highly portable equipment in the microwave bands up to 47 and 76GHz.

Amateur TV Bands

Ranges you can achieve with ATV

The latest developments have seen the 50 MHz bands brought into use around 51.7MHz as it only needs ~300kHz of bandwidth which is achieved by DVB-S2 (QPSK) and High Efficiency Video Coding (HEVC, H265 picture coding, but does need very linear amplifiers. This ongoing progress has recently seen the top of the 29MHz/10m band now also available in the latest band plans for DX experiments. QPSK based modes remain the most common but ongoing work to develop narrowband OFDM is underway which has better multipath performance for long distance DX.

David showed how BATC and others had adapted Raspberry Pi’s, but also designed and made available DATV equipment such as the ‘Minitoune’ receivers and ‘Portsdown’ DATV transceiver.

Portsdown DATV Transceiver

Another landmark facility is that the QO-100 geostationary satellite has a DATV transponder enabling huge coverage over Europe, Africa & Middle East etc. Uplinks are in the 2.4GHz amateur band with downlinks in 10.4 GHz very easily receivable using a modified LNB. To assist CQs and operation, there is an online SDR at Goonhilly which also has a chat-text window.

MiniTiouner DATV Receiver

QO-100 Satellite has a DATV Transponder
It is not entirely digital. Beginners can have fun by adapting low cost consumer FM camera modules on 5.6GHz originally designed for drones that can be easily converted to the amateur allocation. BATC which has ~1400 members, also has an online wiki, forums and an online video streaming facility where many of the repeaters and other events can also be more accessible via the internet too.

During Q+A it was pointed out that Jeremy Royle did an early TV talk at CARS in December 1965 and that Tony Gilbey G4YTG knew Mike Barlow G3CVO at founding of BATC many years ago.

Many Thanks David!

Getting started on DATV

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