14 Feb 2019 – Aircraft Communications by Don, G4LOO

Don started by pointing out that most people think only of air to ground voice communications as being the sum total of the use of radio. There are, however, many other types of radio signals in use, beside voice there is radar and data.

Don went through the communications used to help the pilot know his location and point to the destination. Following that, Don detailed radio used for instrument landings indicating the aircraft position with regard to the runway, the glide slope and markers at three critical distances to landing. But, it was also pointed out that important information can be automatically transmitted to indicate position, aircraft operating parameters and aircraft ‘health’ to ground stations. During long flights, including overseas trips, automatic transmissions can be made to satellites designed to work with the aircraft information.

The question was asked as to why signals of this sort couldn’t be used to locate a plane that had gone off the radar map. The answer being that the transmitting units, in this case, must have been turned off. The next question was why be able to turn the system off and the answer is that they must be turned off when on the ground to stop multi transmissions from various planes interfering with those in the air.

Don showed a diagram of a typical airliner pointing out the locations of various antennas, there can be over twenty!

Tipical antenna locations

7 Feb 2019 – Construction Contest Winners Talk

First up was Martin, M0XMP who won the kit class section of the contest with his QCX 5w CW transceiver. This kit supplied by QRP Labs is very complete and the downloadable instructions, all 142 pages, were described as ‘like Heathkit’ on steroids!  Martin showed his copy with each part described and followed up with a colour illustration as to where and how it should be fitted.

Martin was especially pleased the unit came with a built in signal generator and alignment tools as well as a voltmeter, RF power meter and frequency counter so the builder does not have to have a workshop full of test equipment to get it going.  Martin demonstrated the unit decoding CW and it was pointed out that it can also be used for stand alone WSPR transmissions.

All this is very impressive for the modest price being asked. See all the details at:  www.qrp-labs.com               or watch a video at: https://www.youtube.com/watch?v=6zlCuPq2aNA

close up of part of instructions with red squares showing where to insert 100 nF capacitors

 

Don, G4LOO won the Weekend Special with his very simple project used to locate dislocated buried radials. The idea came originally from a published article which could easily be adopted and implemented. Don found that rabbits had been chewing the ends of his buried radials at the central connection point at the base of his four square antenna. Using this unit Don could  walk along  the area over the radial and carrying a small MF radio taped to the end of a cane (like a metal detector) could listen for a null and thereby detect the broken wire.

Radial pattern for 80m four square antenna

31 Jan 2019 – Antenna Modelling by Gareth, M5KVK

Sample Plot using MMANA-GAL

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.