Talks presented in 2024

GB3SW repeater updated and working - 29.01.2025

Dave, G6XUV and Jason, the principal actors behind the 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 has taken 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 has been 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 the 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 a 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.

Visit to Mike Marsh Mastering - 30.03.2026

The committee members of the club have organized a visit to the Mike Marsh Mastering Sound studio. It is great to see a member opening his workplace for a visit, and it was a very unique experience to visit Mike in his studio.

Let's first explain what mastering means. As an artist records and mixes their music, it is necessary to audit and improve all tracks which will compose a vinyl, CD or digital release.

This process usually starts these days with receiving a digital audio record (usually in WAV file format) which is then read by a computer and converted to audio signal. The music is being played on the studio sound apparatus, which comprises a series of equalizers, preamplifiers, sound monitors and analyzers. Finally, the music is sent to massive speakers - called monitors. Before the music can be played in the speakers, the signal needs to be amplified using valve amplifiers to provide the best possible quality of sound.

Mike has shown us some of his techniques, how he used to process recorded music before receiving big tapes, or a DAT tape recorded with music.

That all is a distant past now, as everything became a question of the Internet and WAV format. As your webmaster has studied electrical engineering at university, let's dive into forgotten knowledge about audio format. One thing you need to know is that WAV format is stored in linear pulse-code modulation in an uncompressed format sample at 44.1 kHz with 16 bits per sample. The data are wrapped in the RIFF wrapper - the data contain four character tags and the size of the data chunk. A usual C/C++ technique would be to read the header and then set the buffers to read the data. There is much more to it, but I believe a technical society should not shy away from difficult stuff. In the end of the day, most of us will use a standard library to read the file anyway.

The next interesting thing was to look at the process how vinyl is mastered and then written to the master vinyl. A less well-known thing is that there are only 100 machines worldwide which can do the task - it is called lathe and the most famous was made by company Neumann. The task itself is based on conversion from a music track (sound signal) into a mechanical oscillation of the diamond tip, writing into lacquer - it is not a vinyl but a special vinyl-looking surface, which can be cut by that small tip.

As Mike explained, the ubiquitous battle with noise continues always, and vinyl recording is no exception. The inner tracks of the vinyl are being read with a different speed, and also their vicinity to each other needs to be taken into account when producing master.

I was looking forward to seeing the machine itself, but sadly, Brexit, market conditions and others made Mike to sell his sound lathe some time ago. As any business, he must fulfill the market needs and keeping an expensive instrument just as a nostalgia piece could be costly.

But don't despair - you can read a 17-part series about acoustic cutting lathe clicking on the link.
Around the world in 80 lathes part one

There is everything thinkable about the subject, and it is a fascinating reading.

Let's now say a few words about the studio. As Mike worked 30-years in London. his requirement was to build the same dimensions studio as he had. This is critically important as his custom-made speakers and the "production line" is his gold standard for the sound and the room design must have been providing the same audio environment. The music must always sound the same.

As one of the club members has built the studio on Mike's order, we could get a glimpse of detail what is involved in building a soundproof studio. And it is a lot involved! Thick walls, double walls, various dampeners and methods to stop the sound expanding into the space.

Mike then showed us the technicalities of the process of mastering the sound recording. 2 very interesting devices are for measuring the stereo balance between the left and right channel. The photo explains more.

An additional device is a sound spectral monitor. With amplifying and equalizing various frequency ranges, it makes it an interesting challenge.

Mike records all his work in his workbooks. He can then reproduce everything as the original work was done. The digital era is a data destruction era, so it is great to see somebody recording his protocols so meticulously.

Mike has answered many questions and played some of the very old vinyls. The key question to me was - what makes good music?

And Mike's answer was simple: Good music energizes!

Amazing stuff!

P.S. A few days later, I'm reading a book ReaMix: Breaking the Barriers with REAPER. It is a great book, but the visit to the studio has made its reading so exciting with the hugely increased ability to understand what the author is talking about.

Mentioning external references - it is worth mentioning Sigma DSP studio - free of charge which allows designing audio processing pipelines and creating a configuration for Sigma DSP chips.