28 Feb 2013 – The Smith Chart

40m Phased  Verts

It’s enough to strike terror into the hearts of many radio amateurs who had to learn how it worked and how to use it.

However, Stewart, G3RXQ showed that it’s not quite as complicated as first thought and the results can lead to an efficient antenna that really ‘gets out’.  Many amateurs are lead to believe that buying an ATU, or more correctly, an Aerial Matching Unit, can solve most antenna problems just by presenting the transmitter with a 50 ohm load.  These units might be more correctly called ‘Transmitters Tranquilizers’ since they do nothing to tune your antenna, only keep the transmitter happy, while the un-resonant antenna at the other end of the transmission line might be wasting up to 95% of the power presented to it, leaving only a few watts for actual transmission.

By using an ‘active’ Smith Chart, Stewart showed how the situation could be visualised and also what was needed at the antenna end in the way of capacitance or inductance to match the antenna impedance, thus using almost all the power for transmissions.

The ‘active’ Smith Chart can be found on the internet at: http://science4all.nl/?Electronics::Pasan  This excellent programme was written by Marien van Westen (PA0MVW) and offered, free of charge.     It brings the Smith Chart of 1939 right up to date!