Category Archives: meeting report

August Meeting Report

At a well attended August meeting, Giles G0NXA introduced us to the basic principles of antenna matching and the Smith Chart.

smithchart-audience

Giles explained that we need to match the antenna to the feeder for three main reasons:

  1.  to maximise power transfer,
  2.  to minimise the SWR (standing wave ratio) on the feeder so as to avoid power fold-back or shut down by (solid-state) PA protection circuitry,
  3.  to minimise power loss in the feeder (which can occur with a high SWR).

He then went on to talk about complex impedances, how they can be described and measured, and concluded with a description of the Smith Chart as a method of solving matching problems by graphical means.

Another very good club meeting, with lots of interesting and useful information being presented.  Many thanks go to Giles G0NXA for giving us the talk and for presenting the information in  a readily understandable manner with many tangential stories to illustrate the points he was making.

Many thanks also to Peter G3YJE for yet again manning the tea/coffee bar – volunteers for future months would be most welcome.

Derek G3NKS

July Meeting – Restoring an Air Ministry T1154 and R1155

This month we had a very interesting talk by Tony, G3YYH, who is working to restore an Air Ministry T1154 transmitter and T1155 Receiver, or, as I tweeted at the time;

The radio was designed in the late 1930s, around 1939 it went into production at various manufacturers, with production continuing throughout the war.

Around 75,000 R1155 were produced, Tony tells us

I can’t tell how old mine are, but I’m fairly sure the R1155 is an early one because it has the early tuning knob that W/Ops hated and was therefore replaced

Tony discussed the various issues with restoring these radios, from difficulty finding suitable screws (apparently BA or British Association aren’t hard to find, but new ones aren’t dirty enough) to lack of spare parts.

Because so many were made, it was common for hams, and other  hobbyists, to butcher the radios for parts, or even just to get a good box. Sadly there were some guilty parties in the room.

As these radios were designed or, and used in, aircraft, they have some interesting and unique features, such as a Morse key specifically designed to be immune to vibrations, and not produce sparks, as the operator would be sat between, and often in, the aircraft’s fuel.

The radio would also be directly connected to the aircraft’s internal headset system, and as Tony doesn’t have a whole Lancaster in his shack, he’s had to produce his own.

Tony’s radios are mostly in fully working condition, although no one replied when he called CQ in voice, or CW

And finally, for those who like to see the inside of things…