Mark began with a survey of members to find how many, the type and age of their meters after he said his presentation would detail multimeter types and uses, vintage examples from his collection, taking readings and understanding the uncertainty, ending with making and using precision references which he had brought to display.
Mark showed a few meters and how they should be used, followed with photos of several vintage models, dating from the nineteen twenties, including the fascinating ‘Pocket Watch’ model. He also showed photos of advertisements from the British Vintage Wireless Society and gave comparisons prices in today’s money which indicated they certainly were not inexpensive.
It was explained that even with today’s modern meters, it was necessary to understand the uncertainty of the readings. The list of parameters to assure the ‘goodness’ of readings included: Error, Validity, Reliability, Repeatability, Accuracy, Precision, and Resolution. Mark explained just what these terms meant. The first being: “In all measurements there is a certain degree of error present. An error is the deviation between the actual value of a measurand and the indicated value produced by a sensor or instrument used to measure the value. Error is inherent and is not the fault of the person making the measurement. Error is not the same as a mistake! Measurement error can be minimised by procedural methods.” (JosephJ Carr – Practical RF Test and Measurements: A Technicians Handbook)
Each of the remaining parameters was explained with the same thoroughness. Mark ended by detailing the precision references available commercially or to build and the members then had a chance to test their own meters.
This was the last meeting before the summer break. Regular meetings will resume on 13 September.
A very good turn out heard Brian Hawes tell of the progress in U.S. Photo Reconnaissance since the end of WW2. Early information was gained by use of existing military aircraft, but the range and altitude was limited. In May 1960 the world became aware of the U2 aircraft when one was shot down by the Soviets.
From the U2 to some of the latest satellites, Brian detailed Photo methods and equipment. The earliest satellites using film were limited by the fact that the film had to be recovered from space and developed before intelligence could be gained. Once the film was used up, the satellite was allowed to burn up by falling to earth since it could not be reloaded! The advent of digital photography meant better photographs and near instant recovery of images.
While most of the information appears to be Top Secret, in fact, it has now been downgraded and is even being published in a Haynes Manual!
An 18:30 start saw a dozen members meet at the RSPB headquarters at Sandy for an evening tour of the grounds. Two guides divided the group in half and each started off in a different direction. We were shown how areas of land are being managed to provide habitat for different birds and other animals. The tour guides provided a commentary as we spent the next hour and a half following trails finally returning back at the starting point
David Lloyd, G8UOD found us after about 50 minutes and travelled 15.4 miles. Gareth, M5KVK who did not have a directional antenna ran out of time when we called it a day after an hour.
As for the location, we were parked under trees on a triangular grass area at the intersection of three roads in Shillington. We all met up at the Brewery Tap afterwards.