Chelmsford Amateur Radio Society

CARS Meetings April - June 2015

Award for All

7th Jun 2015

Added June Meeting report on Microwave Operating

April Meeting
Tue 7-Apr-2015, 7.30-10pm
Oaklands Museum, Moulsham Street
"Raspberry Pi"
By Peter Onion G0DZB & David Whale

First released in Feb-2012, the Raspberry Pi has been a best-selling phenomenon with over 5 million of these low cost credit-card size computers sold.

They use an ARM processor, can run Linux and have a variety of options for interfacing to sensors and radios. Originally targetted for educational use, a whole community has grown up around it.

Peter G0DZB was joined by co-presenter David Whale who is a STEM ambassador and Pi expert. Peter introduced the Pi hardware and accessories in its various guises, whilst after the break David showed its software and how it was used in schools.

Peter started his talk with some of the history and aims of the of project, which was to re-introduce programming skills into schools, as these had declined considerably since the days of the ZX-Spectrum, BBC Micro et al. The Raspberry Pi Foundation owns the designs but relies heavily on RS and Farnell (and Sony manufacturing in Wales) along with a host of support by the wider community. Since the introduction of the original A and B models in 2012, a series of revisions has led to a number of newer versions, as Peter illustrated in this rather neat slide:-

Raspberry Pi models

Peter went through the basics of what is required to get the Pi going (monitor, keyboard/mouse) and gave some tips on powering it - a steady 5v supply is required, not a cheap USB phone charger! One of the many accessories available is a Pi-styled USB hub which relieves the power supply load for USB peripherals.

With the latest Pi2 model just released, Peter explained that with four 900MHz cores and 1GB of RAM, you essentially have a "computer" that can be used for e-mail, web-surfing, music playback. It may not be able to do it all at once, but it is certainly useful as a simple "surf the net" system. Many are used without a screen simply as a file-server, perhaps to distribute music/video around a home network.

The input/output pins on the Pi make it easy to connect buttons, sensors and LEDs which can be used to teach electronics and programming. The Python language is typically used, as well as a system called "Scratch" that encourages youngsters to build programs by dragging, dropping and joining code-blocks to create a working application. With a wide range of sensors available, low-power and compact projects such as weather gauges, wildlife recorders are all within the grasp (and budget) of most.

For demonstrations, Peter had Pi's connected to a small tablet and a LED Array

Peter finished by saying that help with coding was readily available through forums, social-media and a growing community of Raspberry Pi "Jams". The latter are regular meet-ups where ideas can be discussed and assistance given.

After the break and raffle, David Whale explained his role as STEM ambassador and how computing and coding in schools had become stagnant since the decline of the BBC Micro and the introduction of the Personal Computer. With the Pi (and cheap electronic accessories) comes the ability to easily transport up to 50 "computers" for a lunchtime "Pi Club".

Portable kits and a trolley faciliates enables a quick setup and classroom use

Quite a number of visitors were present, and CARS had its famous raffle which included two Pi's as prizes.

The top CARS Raffle Prize was a new Pi-2

David Whale (left) drawing the raffle - and David Ingrey M0HBV receiving his Pi Prize from Carl G3PEM

A CARS tradition - our speakers with their CARS Mugs

A good evening, which was very well attended by ~60 people - many thanks.
All photos above by Murray G6JYB

Useful Links:-

  • Raspberry Pi: Main Pi website
  • David Whale: Pi Blog

    May Meeting
    Tue 5-May-2015, 7.30-10pm
    Oaklands Museum, Moulsham Street
    "Operating Portable"
    by Charlie Davy M0PZT

    Operating outside the four-walls of the Shack presents a wealth of opportunities (not-to-mention hurdles) for the Amateur. Fresh from organising the outdoor GB1STG Special Event, in this talk, Charlie outlined his 'Big Three' - "Whys, Wheres and Hows", of portable operating.

    Charlie introducing the topic - and his portable kit

    Operating outdoors requires preparation and can be a challenge. However it has the benefits of:-

    • Escaping the restrictions of a home qth (neighbours, small gardens etc)
    • Quiet RF Location - can be near zero noise
    • An Opportunity to Experiment
    • A Social Event - can be a group event, or attract visitors
    At 85m high, Galleywood Common is a one of Charlies favourites but there are others around Essex (though no Summits!). Around fifty people attended to hear a great presentation all about portable operating, including quite a number of visitors.

    Telescopic Fishing Poles are a popular prop for HF antennas

    Both HF and VHF antennas were a key topic

    Preparation as well as safety outdoors is of course important and tips included first aid kit as well as:

    • Keep Cables Tidy - dont trip!
    • Battery safety - dont let dogs sniff/lick them!
    • Bright Colours - bright yellow aerial wire, tent pegs etc avoid losses and trip hazards
    • Secure the Poles - Ensure aerials are secure, inc cords, cable ties etc

    Charlie had a good deal of kit on display (with a few extras courtesy of Peter G0DZB). The single largest was a home made 'Porta-frame' that can hold his FT857, battery and accessories and fit in a ruck sack. It was soldered together from a total of ~4m of 15mm copper water pipe to provide a robust structure.

    Handmade carrying frame for an FT857 and accessories

    As per some other recent talks the CARS raffle had some themed prizes - this time it was for "portable" (acquired from SOTAbeams) - won by Martin G4TOO

    Portable Kit Raffle Prizes - and lucky winner Martin G4TOO receiving the dipole kit from Chairman Chris G0IPU

    Useful Links:-

  • Checklists - Essex Ham
  • ARPOC - Amateur Radio Portable Operators Club
  • SOTAbeams

    June Meeting
    Tue 2-Jun-2015, 7.30-10pm
    Oaklands Museum, Moulsham Street
    "The Bodger's Guide to Microwaves"
    By John Worsnop G4BAO

    The greatest DX is not on HF but on the microwave bands, which are home to construction and innovation (much of which feeds down to lower bands). Without microwaves there would be no smartphones, Wi-Fi or SatNav.

    Dr John Worsnop G4BAO who is the treasurer of the UK Microwave Group and a member of the RSGB Propagation Studies Committee travelled from his Cambridge qth to enlighten us as to what is now possible.

    John's talk first covered a bit of history from the first QSOs in the 1950s, but he was keen to dispel some of the common myths related to propagation and distances. The focus was on narrowband terrestrial DX, but he was also keen to point out other aspects includes data links, satellites/ISS, moonbounce (EME) and amateur TV.

    A distinguishing feature of microwave bands is the availability of high antenna gains and the absence of atmospheric noise making it worthwhile aiming for state-of-the art Tx stability and Receiver performance. This has driven new GPS-locked sources and innovative modes such as JTxx (initially for moonbounce) that have all rippled down into the lower amateur bands.

    John G4BAO with a high gain 23cm Yagi Antenna introducing his talk

    Why Bodger? - well it highlights that microwaves is a field where DIY/Construction is alive and well - although nowadays many items are available off the shelf as well. The amateur licence gives us access to a huge amount of bandwidth relative to HF, so you certainly aren't as limited to just narrow modes, but the move from the original very wideband sources to narrowband did offer huge benefits. In terms of history, John gave a quick summary of how technology had evolved (and continues to do so) over time:-

    History in the UK

  • 1950: first 10GHz QSO - 1.7 miles between G3LZ - G3BAK
  • 1960s - Klystrons
  • 1970s - Gunn diodes ( eg doppler alarm modules)
  • 1980 - Narrowband technology introduced - G3JVL Low Power waveguide transverter (Tx 0.5mW, Rx 8dB NF)
  • 1990 - First microstrip/PCB modules introduced by Charles Suckling G3WDG

    Nowadays most solutions are 'silverboxes', (not black ones). Whilst HF Receivers may have a noise figures of 15dB, amateurs have pushed the state of the art at microwaves with the G4DDK VLNA designs being ~0.2dB

    Modern microwaves - a 23cm Very Low Noise Amp (VLNA) by Sam Jewell G4DDK

    Advances in transmitters have been helped by both synthesisers and GPS. This becomes increasingly important if you wish keep your few kilohertz of CW/SSB stable at for example 75.976 or 134.928 GHz calling frequencies. Much of the UK microwave beacon network is now exploiting sources like this so you can often be sure you are accurate to a few Hertz!

    Modern microwave sources exploit the latest synthesis techniques

    John was keen to dispel three Myths - that it was line of sight (ie not much DX), that it was expensive and that it was overly technical. His qth in Cambridge is barely above sea level but his 23cm and 10GHz kit had achieved very impressive QSO distances acrosss the UK and Western Europe. Modern kit often uses transverters that can be driven for a common multimode such as a FT817.

    Dispelling the Myths - Its not too dear or technical - and you can certainly do DX

    Having highlighted the 1000+km distances he had achieved, he then went on to explain the propagation mechanisms. Most are natural, but a recent one exploits knowing flight paths - for Aircraft Scatter QSOs.

    • Optical: 24/7 – Line of sight – hilltop to hilltop
    • Tropo: Enhancement and Ducting - weather–dependent – Enhanced range up to 2500km (esp if near the coast)
    • Tropo Scatter: 24/7 – Over the horizon up to 500km - esp if you have some power
    • Rain Scatter: Weather–dependent - Over the horizon up to 800km
    • Aircraft Scatter: 24/7 – Over the horizon up to 800km

    Modern Microwave DX is very directional and long range, resulting in 2m talk back falling out of favour and the Internet helps instead. Most terrestial microwave DX/spots are notified by chat rooms, of which ON4KST by far the most popular. Modern technlogy and free software also helps those who want to start on a low budget - John had a low cost Dongle and SDR-Touch on a low-cost Android tablet that could receive 23cms inc the GB3MHZ Martlesham Beacon. UK Microwave Group (UKuG) membership , which is just £6/year, entitles you to the monthly 'Scatterpoint' magazine, free surface mount components (the UKuG 'chipbank') and a lot of technical advice and elmers.

    Getting Started can be as simple as a USB Dongle for 23cm reception and a look on ON4KST for QSO activity/spots.

    Carl had organised the CARS Raffle Prizes whilst John G8DET managed the draw. Carl also maintained the tradition of presenting the speaker with a souvenir CARS Mug!

    John G8DET running the raffle - and Carl G3PEM presenting the CARS Mug

    Our thanks for a most enlightening and well presented talk. You can see John at Microwave Roundtables, the RSGB Convention in October or the monthly Codgers 'Last Saturday Breakfast' near Orwell.
    All photos by Murray G6JYB

    Useful Links:-

  • John G4BAO website:
  • UK Microwave Group: UKuG main website
  • ON4KST: VHF / Microwave Chat Room
  • Beacon Reports: BeaconSpot

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