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Chelmsford Amateur Radio Society

Smith Chart Calculators

On Sunday 12th August 2007, Murray Niman G6JYB of the Chelmsford Amateur Radio Society (CARS) presented two rare Smith Chart calculators to Trish Robinson of the Sandford Mill Museum.

Trish & Murray, G6JYB
Trish Robinson, on behalf of the Museum, receiving the Smith Chart Slide Rule from Murray, G6JYB.
Photo by Trevor, M5AKA - Click for Medium Resolution

The calculators were made by Scanners Limited of Bill Quay, Gateshead. They made the gimballed platforms for the radar division of the Marconi Wireless Telegraph Company. Eventually Scanners Limited were bought by Marconi and became a manufacturing and assembly plant for Marconi Radar.

They were owned by Mr H M Chandler (known as Vic to his friends) who worked at the Gateshead plant from the late 1940s to late 50s. Vic died some years ago and they were found by his son Nick Chandler following the recent death of his mother and consequent house clearance. Nick, a Chief Scientist at BAE Systems, Great Baddow, Chelmsford gave them to Murray G6JYB.

The Smith Chart Calculator
The Smith Chart Calculator
Photo by Trevor, M5AKA - Click for Medium or High resolution

Smith charts enable plotting of impedance, Z and its inverse (i.e. admittance, Y) for design of matching circuits - a process that is usually performed by computers nowadays rather than by hand. The central circular chart can be rotated and the picture shows them in the rarer Admittance position - as used in the Marconi and CARS roundel logos. Normally they are used 180 deg around in the Impedance position. The chart was developed by and named after Philip H Smith in 1938. His original book is a collectors item.

In addition to the calculators the Marconi company printed a wide range of graph papers and pads including Smith charts under the MG (Marconi Graph) series.

Useful Links for Further Reading

Philip H Smith

The Smith Chart

Bill Quay, Gateshead and Culture/ls/Places/Bill Quay.aspx

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Chelmsford Amateur Radio Society 2007
Last revised by Murray G6JYB - 5-Sep-2007