Chelmsford Amateur Radio Society
G0MWT, GX0MWT, GB5HF, GB100MWT & GB95-2MT

CARS Meetings: Jan - March 2020




January Meeting
Tuesday 7th Jan 2020, 7:30-10pm
Oaklands Museum, Moulsham Street
"HF Propagation"
Steve Nichols G0KYA

Early January is often an awkward slot to get speakers to travel. This year RSGB Propagation Chairman Steve Nichols G0KYA kindly made available new copies of a pair of talks he had pre-recorded complete with extensive audio commentary and show notes.

So the new year began with an beautifully crafted HF talk which was ably introduced and compered by Chris Chapman G0IPU, complete with interactive Q+A at key points thru the show.

The novel format worked particularly well on the room projector and audio system.

Note: Colin G0TRM plans to feature the shorter VHF talk as one of the '3 Short Talks' later this year

The first CARS raffle of 2020 created some happy faces

 

The accompanying talk notes had lots of links for further information including these:-

Space Weather

  • www.solarham.com - SolarHam
  • www.swpc.noaa.gov - Space Weather Prediction Centre

    Propagation News

  • RSGB: GB2RS Propagation News

    Ionosondes

  • car.uml.edu/common/DIDBFastStationList
  • www.ukssdc.ac.uk/ionosondes/
  • Ionospheric sounding and digisondes

    Prediction Tools

  • Propquest: www.rsgb.org/propquest - real-time MUFs
  • Predtest: www.rsgb.org/predtest - path probabilities for different modes - by Gwyn G4FKH
  • VOACap: www.rsgb.org/voacap - propagation to 28 global locations, as used for RadCom
  • Proppy: www.rsgb.org/proppy - uses the latest ITURHFProp tool for the same 28 locations

    Post Meeting Note: This HF video was released by RSGB on to Youtube on 9-Apr-2020 during the Coronavirus lockdown period. Click to Watch



    February Meeting
    Tue 4-Feb-2020, 7.30-10pm
    Oaklands Museum, Moulsham Street
    "OAS & Portable Operation"
    By Dave Cutts M0TAZ

    The February meeting had a good turnout for the return of Dave Cutts M0TAZ who updated us with a double bill consisting of:-

  • The new RSGB Operating Advisory Service - for which Dave is the Region-12 rep
  • Operating Portable - though with a few differences!

    Dave started with a brief overview of the new OAS which has replaced AROS. Whilst AROS volunteers were kept secret and supported Ofcom, the new approach is a far more public and broader one. Under the overall OAS national coordinator are OAS regional operating advisers working in liaison with the existing RSGB Regional reps. The OAS role is to:-

  • Advise local amateurs - via club presentations and responding to cases
  • Share experience nationally - what has helped elsewhere
  • Promote good practice to help you control the situation.
  • Potentially assist new amateurs with operating advice (inc one-to-one for RSGB members)

    The OAS will not:

  • Intervene personally (it makes matters worse)
  • Give legal advice (they are not qualified to do so)

    In the case of on-air abuse remember to never respond to on-air abuse in any form. More about OAS is at: www.rsgb.org/oas

    Dave then moved onto one of his own favourite topics – portable operating:-

    His slides covered the various motivations, considerations and benefits from getting out to rf-quite countryside for some DX from decent heights.

    Whilst much portable operating is associated with QRP (and Dave has had a go at that), he has also tried his hand at more power. However the big cautionary note is that needs a generator as it is all too easy to flatten your car battery!

    Dave is also a DIY fan when it comes to antennas. Rather than spending £99 on a CWA1000 kit, one of his preferred arrangements is below, which has the added benefit of not needing an ATU


    A QRP modem for PSK31

    One of Dave’s Antennas for Portable use

    Our thanks again to Dave for another great presentation



    March Meeting
    Tue 3-Mar-2020, 7.30-10pm
    Oaklands Museum, Moulsham Street
    "Measure It!"
    By Dave Ellis G4AJY & Bob G4MDB

    The March meeting featured a double instalment on measurements - classical and modern.

    Meters: Dave Ellis G4AJY started the first session with the moving coil meter. These may seem to be out of date in the modern ham radio scene, but they can still do things that a digital multimeter cannot - and you can pick them up for as little as a pound at a rally.

    Dave started with the 'back-to-basics' of how a moving-coil meter is made and how it works. He noted that on better meters there are mirrors to avoid parallax errors when reading the needle. Simple applications of course include using it as a Voltmeter, Ammeter or Ohmmeter.

    Whilst DMMs can be superior in some cases (esp in high impedance voltage measurements), the inherent inertia of the moving coil mechanism lends itself to be rather handy. Dave explained how it can rms average variable/pulse waveforms.

     

     
    Dave Ellis G4AJY - From the basics, to useful properties of moving coil meters

    This led Dave to show some special projects for a moving coil meter, including a frequency counter and a Morse Code WPM speed meter.


    Dave's Moving Coil Morse Speed meter

    So dont ignore cheap/surplus ones in a rally. Every ham shack should have one!

    VNAs: After the break and raffle, Bob Tokley G4MDB gave an insight and demos of another measurement tool - really useful for Antenna Design & Measurements.

    Bob started with more classic equipment such as SWR meters and the Bird power meter. He then went on to describe and demo the operation and functions of his two miniature Network Analysers as Bob owns both a miniVNA and a NanoVNA. The latter model includes its own small display.

     
    Bob G4MDB and some of his test items

     
    VNA models

    A Vector network analyser (unlike a Scalar one) can measure both the amplitude and phase of reflected (S11) and tranmission signals (S21). Amplitudes can be displayed in dB or VSWR vs frequency, using its own internal source and receiver. Using the phase information, additionally impedance can be plotted on Smith Charts to give insights and assist matching circuit design.

    Our thanks to Dave & Bob for insightful presentations and hands-on hardware demos.

    Useful links:

  • CW Meter: August 2012 Constructors entry
  • minVNA: miniradiosolutions.com
  • NanoVNA: nanovna.com


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