RadCom 'Antennas' column supplementary material

In the January 2009 edition on Antennas in RadCom I described methods of measuring impedance and admittance.

I also described how you can make a simple impedance calculator (Smith Chart) using charts supplied here. 

You can obtain these charts by clicking on  Smith to download them. They can then be printed to form the basis of your calculator.

There are three separate charts in the zipped folder.

Smith Chart 50RR is based on a 50 Ohm prime centre and has a restricted impedance range, which would result in an SWR of less than 3:1. It is much easier to read than a full Smith Chart.

Smith Chart 50 is a conventional Smith Chart  based on a 50 Ohm prime centre. Both these charts are suitable for calculating coax cable electrical length, determining coax velocity factor, calculating antenna impedance from measured impedance and determining SWR of a given impedance - all on 50 Ohm systems.

Smith Chart Normizd is a normalized Smith Chart, which can be be used at any impedance and not restricted to 50 Ohms like the previous two. This is achieved by assigning 1 to the prime centre. This chart can be used to convert admittance to impedance.

Construction and use of the charts is described in The Antenna Experimenter's Guide, Second Edition from RSGB bookshops.

The transmission line calculations are more easily done using appropriate computer programs these days. The main reason for including the Smith Charts is that you can learn a lot about transmission line calculations by using them.

A suitable computer program can be found at www.vk1od.net/tl/tllc.php.

If you are only interested in in converting Impedance to Admittance or Admittance to Impedance a very simple and easy to use program, written by Rik Strobbe, ON4YD, can be downloaded by clicking ZYconv.

February 2009 Antennas was devoted to the RG 1602-B Admittance Meter. Some readers apparently have this instrument but not the Instruction Manual. This manual can be obtained from http://bama.sbc.edu which is run by Ken Grimm, K4XI.

BAMA, which stands for Boat Anchor Manual Archive, is an excellent service by K4XI to those in Ham Radio who have an interest in restoring or operating older radio equipment or test equipment. If you have any difficulty in downloading the RG 1602-B manual you can download it by clicking 1602.

Updated 2nd Feb 2009