On a very cold evening on the last day of January, we were expecting some snow but members turned out to hear Gareth present his introduction to antenna modelling. He stated he would give a gentle introduction to modelling back garden antennas. The presentation was not meant to be the definitive guide to modelling antennas but more of what you might achieve. Gareth stated that modelling is not too difficult, provided you don’t expect perfection. It can provides a lot of insight into how your antenna works and provide a good basis for making improvements.
He then went on to list the programmes available, either free or ‘paid for’ and explained what can be expected from each. One that he tried was MMANA-GAL which was provided on a CD with the RSGB’s “Introduction to Antenna Modelling” by Steve Nichols, G0KYA. This free programme does have some limitations but can be useful as a start.
Next examined was EZNEC, not free, but there is an EZNEC Demo which is free but limits the complexity of antennas you can analyze. Gareth also mentioned ‘Transmission Line Details (TLD)’ which calculates SWR and loss for lengths of transmission lines of different types, a good addition to antenna modelling situations.
A live demo then followed with several examples, one of which was Ian’s massive doublet, 360 feet long and up 60 feet. The doublet ends are supported at 46ft and 29.5ft high, the system is fed with 400 Ohm ladder line. Although the PC took a while to compute, the result showed that matching would be possible on all bands, 160 to 10m, with the best match on 20m.
Gareth said Part 2 would focus on a practical application of this software.