Chelmsford Amateur Radio Society

CARS Meetings   July - September 2016

Award for All

28th Sep 2016

Added September mmWave talk report

July Meeting
Tue 5-Jul-2016, 7.30-10pm
Oaklands Museum, Moulsham Street
By Justin Johnson G0KSC

Local amateur and entrepreneur Justin G0KSC (InnovAntennas, W&S, Force-12) came to CARS to present a talk on antenna design including novel Yagis. Justin is well known for his pioneering and very successful work including modelling and optimisation for low noise and sidelobes - as well as the materials to make the real thing!

In March 2016, Justin was awarded the '1962 Committee Cup' by the RSGB for his contributions to VHF antennas and in particular the development and publishing of the LFA antenna design.

His latest work on 'bent yagis' was presented (as recently seen at Dayton). Justin slides covered some of the history of bent elements including the Moxon and others; and then proceeded to cover his own work with NEC modelling qnd adapting the idea to his own antenna designs.

Extracts from Justin's talk on bent elements

Following the presentation and tea break, the famous CARS Raffle was held

Chris G0IPU running the raffle

One final matter was the traditional presentation of a CARS Mug to the speaker...

CARS President Tony G4YTG presented Justin with a CARS mug

Our grateful thanks to Justin for a most interesting and absorbing talk.

Useful Links:-

  • Justin:
  • UK:
  • USA: Force12 inc

    August Meeting
    Tue 2-Aug-2016, 7.30-10pm
    Oaklands Museum, Moulsham Street
    "Constructors Competition"
    By CARS Members

    The August meeting was the annual time to show what had been constructed - be it a Linear, QRP Transceiver, an Aerial or some Radio Software. CARS accept all sorts of entries (and have done so in the past) from still photographs to video clips. The only real Rule is that it must be electrically SAFE.

    Over thirty people attended on a very warm evening to see a wide variety of entries. CARS ex-President Carl, G3PEM was the host for the evening. He started by saying that he is often nervous ahead of the event as to whether there would be many entries. However that was not a problem on the night as we had nine:-

    • Alan M0IWZ - A low cost Weather Station
    • Steve G4GHO - An S-Parameter Test set for his network analyser
    • Steve G4GHO - A kit Receiver
    • Tony G4YTG - DF Antenna with a tracking receiver
    • John G4IMS - Signal Generator Upgrade
    • John 2E0DNS - SWR Meter with Digital display
    • Dave M0HBV - Wobbulator test set
    • Dave M0HBV - Fan cooled 75 Ohm Dummy Load
    • Andy G7TKK - VHF Aerial made from copper tape on cardboard

    Tony G4YTG DF Antenna and John G4IMS Signal Generator Upgrade

    John 2E0DNS SWR Meter and Andy G7TKK Cardboard 2m Antenna

    And the Winners...

    New: Frank M1GFE and his 75 Ohm Dummy load

    3rd: David M0HBV came third with his Wobbulator

    2nd: Steve G4GHO came second with his S-Parameter test set

    1st: Alan M0IWZ was first with his Weather Station

    September Meeting
    Tue 6-Sep-2016, 7.30-10pm
    Oaklands Museum, Moulsham Street
    "Millimetric Microwaves"
    By Chris Whitmarsh G0FDZ

    For September we welcomed back Chris Whitmarsh G0FDZ who had previously given us a talk on the Kent GB3VHF/UHF beacons. Many of you will have glanced at the very highest frequencies shown your licence schedule and thought to yourself "Who on earth uses these frequencies?" Well a small but dedicated group of microwave enthusiasts in the UK do and had an they regularly make QSO's, sometimes at surprisingly long distances and with very low power.

    Chris G0FDZ has been operational on these frequencies for many years and brought an extensive slide set that explained techniques used for equipment on each of the mmWave bands, where the wavelength is measured not in centimetres but in millimetres - the smallest being just 1.2mm.

    At these frequencies coax is lossy, so waveguide is used along with microstrip circuit techniques. Antennas are a mix of horns or dishes. A key benefit of small wavelengths is that the antennas are compact but still give remarkably high gain (often 30-40dB) - the downside of which is you have to point things really accurately, so a common feature on much of the equipment was telescopic sights! Most equipment uses some form of transverter to mix up/down from a baseband transceiver - Chris uses FT817s for that role.

    Some of the components used - Antennas, waveguide and mm-Wave mixers

    Chris has operational equipment for all of the millimetre-wave bands and brought it along to show us, along with his presentation. Depite the construction challenge, it was nice to see plenty of slides of people operating, and quite a proportion were in Essex including from Danbury Hill, Brentwood and Hanningfield Reservoir. Alas John Wood G4EAT who was a keen operator became a silent key in Feb-2015, but Roger G8CUB is now pushing ahead nearby.

    Chris has kit on all the mm bands: 24 - 241 GHz

    Dual Band 47/76 and 134/241 GHz Transverters with Elcom Synthesised LO and FT817 baseband transceiver

    Despite the milliwatt powers, the high antenna gains have given impressive UK QSO Distances including:-

    • 24GHz: 408km
    • 47GHz: 203km
    • 76GHz: 129km
    • 134GHz: 35 km

    That doesn’t include moonbounce which is doable on 24 and 47GHz (with TWT power amplifiers)

    A fuller write up of the talk can be read here (PDF) - by Murray G6JYB

    After the break the talk was wrapped up with lots of questions from the interested audience (some of whom are ex engineers or were intrigued by the construction work). Chairman Chris G0IPU helped draw the raffle and we concluded a really educational and eye-opening evening.

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