November Meeting – Antennas

Although our November meeting was to be an open evening with no guest speaker, the evening turned out to be a really interesting and busy evening with great input from club members.

Les G8AMK kindly stepped-in at very short notice to give us a presentation on the characteristics and effects of antenna wire and it’s diameter on the RF frequency and tuning. Les explained the effects through calculations and graphs and also explained why the K-Factor was so important in the calculations.

Steve G4AUC had brought along his home constructed 4m 70Mhz Dipole Antenna, built using wire elements mounted on the outside of a PVC tube. During testing, Steve found that the PVC had a frequency drop effect on the antenna, so a wire length reduction was necessary.

To complement the antenna theme of the evening Richard G3ZWP brought along his home built Controlled Feeder Radiation (CFR) 4m 70Mhz Dipole. This used a length of Coax with the outer shield stripped from a 1/4wave section at the end of the coax and the coax coiled 1/4wave from the strip point to act as a common mode choke. This configuration produces an antenna with charactistics similar to a center fed dipole. Checking the antenna SWR using a NanoVNA revealed that the antenna elements were slight too long for the target frequency band, but the SWR was reasonably flat across the bandwidth it was tuned for.

During our recent SK equipment sale for club founder member Graham G4DDN (SK), David M0XDF found an interesting german made remote controlled digital clock. With the time being set to UTC, David opened the clock to determine if it could be changed to GMT. With the instructions being in German this needed some investigation, but David was able to change the timezone and the clock now re-sychronises automatically each hour. David noticed that to improve reception, the display is cleared while the clock listens for the transmitted time signal.

Thanks to everyone that helped make this an interesting, useful and fun meeting.