Well, the title says it all! After deciding to go the home brew route, John was faced with solving engineering challenges at every turn; from selecting materials to the finding of specialist connectors and attaching mechanisms.
Before building the beam, however, John wanted to move his mast away from the house and the possible overhang of the newly fitted solar panels. Of course, the original mast was mounted in a large block of concrete which needed to be broken up to release the mast mounting post. The lifting of the post was done with the help of a hydraulic jack.
Those familiar with the look of the hex beam will know it looks a bit like a satellite dish facing upward. John started with extendable fishing poles but found they didn’t have the right amount of bend. Glass fibre poles did the job, and were used. Next was the choice of wire to make the elements. John tried several types and settled on flexweave. Measurements confirmed low SWR for almost all bands, but a little adjustments brought all within useable range with good front to back and forward gain.
John said this was a real ‘labour of love’ and with the help of friends, specially Ian, G3ORG the beam is now up and working well.
Bryan, M0BIK opened the evening with a slide show explaining the ins and outs of conventional power supplies. The choice of components was discussed as to which were better for various applications. It was noted that the later use of toroidal transformers meant a unit of less weight could be made which was more efficient. Various circuit diagrams were discussed with reference to good and not so good practice in design.
Don, G4LOO then took the floor and said he was going to tell about cheap power supplies. His units are based on surplus or second hand server power supplies. They can be found at very low cost from time to time on popular auction sites. Most will provide 12V or possibly up to 12.3V if modified slightly and produce an attention getting 47Amps! Other very small power supplies and converters from the same sites were passed around for members to check.
Paul, G1GSN, then finished by displaying his ‘portable’ LPG gas/petrol generator which was about the size of a suitcase and produced mains voltage. Paul explained the benefits of using LPG outweigh that of petrol in that you are not limited to the size of the petrol tank, just use a larger bottle of LPG.. The gas is more efficient, as well, running for a longer time without topping up. This power unit was much larger than any other shown on the evening, though.
The first offering was a quick explanation of the workings, frequencies and differences between RFID, NFC and BLE systems.
The second video was the 1993 account of AH1A DXpedition to the Pacific Island of Howland which almost ended badly. The Island hadn’t seen rain for almost a year but when the 10 radio operators and 2 US Fish & Wildlife Service Representatives finally settled in, the rain started pouring down and continued for several days till everything excluding the equipment was wet. The water soaked into the earth and the Guano began to smell. One op said the island was like the bottom of a bird cage. High seas meant problems with their sailing yacht anchored off shore in that they lost power and were unable to charge the batteries to get the boat engine started, if needed. The surf continued to run high and nobody was able to leave the island safely.
Fortunately, the wind abated and the surf swell dropped. All departed the island with equipment and tents, albeit six days later than planned, their goals having been achieved.
Richard, G3NII has produced another of his excellent kits for our club members. As you can see, it is very complete and we’re pleased to think the uptake has been very good, even non CW users have opted to build one.
Unfortunately, the list for kits was for members only and is now closed.
Graham started by introducing the members to The Institution of Engineering and Technology. The IET is one of the world’s largest engineering institutions with over 168,000 members in 150 countries. It is also the most multidisciplinary – to reflect the increasingly diverse nature of engineering in the 21st century. The current Royal Charter and Bye-laws of the IET came into effect from 1 October 2016.
Graham was one of 7 members of the Biological Effects Policy Advisory Group within the IET whose task was to determine if there are harmful biological effects of low-level electromagnetic fields at frequencies up to 300 GHz. It was explained that possible dangerous EMFs depend on frequency, magnetic and electric fields, exposure time and distance from the source. While high levels can be problematic, it was shown that for the most part, power levels used in British Amateur Radio are not harmful if precautions are taken.
Based on the FCC bulletin OET65, a safe distance (in Feet) from a Horizontal half-wave dipole wire antenna with a transmitted power of 100W at 3.5MHz is 2 ft., at 7MHz, 3.5 ft, at 14MHz, 7 ft, at 21MHz, 11ft and at 28MHz, 14 ft. In use these wire antennas are usually as high as possible and nearly always at 25ft or more. At 400W the safe distance from a wire dipole is equal, in feet, to the frequency is MHz. I.E. at 28MHz: 30ft. Safe distances from a triband Yagi can be more. These figures do not apply to magnetic loops etc. which can have significantly higher fields depending on frequency and power used. It is recommended the loops are not used in the shack or indoors for transmissions.
A link to an Amateur Radio RF Safety Calculator was given as: http://hintlink.com/power_density.htm