TT23         Aerials and Rotators

          Having reached the ‘three score years and ten’ mark, I decided it was time to put up a decent VHF/UHF antenna using a rotator which had some muscle. Hopefully this would mean that I would not have to go aloft to see to it again for a year or ten. Put up and forget. (until the coaxial cable goes of course.)

I like the 2 and 6 metre bands and have always wanted to go on 4m as well. But I know that getting a tower permit at my QTH would be very difficult and then there’s the XYL and the bank balance to take into account. So what rotator and antenna to buy. I have a substantial pole bolted to the side of the house which used to sport my 2 & 70 combined yagi. My 40 years old rotator was past it so it owed me nothing. It had to go. Aah.

At the Hamfest I talked things over with Waters and Stanton and a Create log periodic yagi was decided upon. This would cover from 6 metres right up to 23cms and all the bands in between, including 4 m, 70 cms, Digital and FM radio, Airband , VHF & UHF TV and anything else you can think of. Very basically it consists of a row of dipoles on a six foot long double boom.

The gain is not wonderful, some 7 or 8 dBd at best, but the SWR of 2:1 at the worst seemed reasonable. The beam-width was going to be wide but the back to front ratio looked impressive. The six foot long double boom with six foot wide 6 metre elements would need a stout rotator and I decided on a Create C5. This is a very substantial chunk of metal with very low gearing, driven by a reversible 2 phase AC motor. This has a variable speed control and does not need a braking system as the torque is really massive. The 7 core cable wires were soldered to the tags provided and connected to the controller. The other end plugged into the rotator, via a nice 7 pin plug, suitably waterproofed. Mains on and it all worked as advertised. I reset the stopped position to west, my least used direction. This just meant operating the controller until rotation stopped and then just pulling off the pointer and repositioning it on the compass rose until it
pointed west. Very simple.

I assembled the yagi in short order. It is beautifully made and was very easy to put together. Strangely, there is a small air-spaced coil at the 6 metre end which allows the two booms to be joined together DC wise. I am at a loss as to why this is necessary but I foresee that this is the weakest part of the whole thing. I did paint it to keep the inevitable bird dropping damage to a minimum. Similarly I painted round the crack where the top half of the rotator joined the bottom half, to ensure the rain would not get in. Interestingly, the rotator has a drain hole in the base to let any internal condensation out. The instructions did not say what happens if bugs get in though! All the antenna fixing bolts got the moly-grease treatment. It will
all be dismantled one day for sure.

I am very grateful to Chris, MØECM, who came round to give me a hand. It was a cold day and I was not feeling too good but he did the biz in no time. There was the small problem with the coaxial cable round the rotator getting snagged up, but that was soon put right. It is important to allow plenty of cable for this. I must get some flexible low loss stuff organised. I re-used some old coax, which is NOT a good idea, see Dec. RadCom) The sun, wind and rain gets to exposed coax and it just doesn’t last. Over the years you just don’t notice the dB loss increasing, but it does. Have you got digital TV yet ? I hope you did not use the same cable for your outside antenna. Get some new low loss 70 ohm stuff from a good source. Don’t buy it if you can see the insulation through the screening. Also, a QRP rig with good quality 50 ohm coax and antenna, will work much better than the latest all bells and whistles expensive high power gizmo with a wet piece of string for an antenna fed by some grotty old coax. Always use quality, properly made up, plugs and sockets, silver plated preferably, properly waterproofed with lots of self-amalgamating tape.

My FT857 has 6 metres coming out of one socket and 2 & 70 from another, so a change-over switch was needed to feed the aperiodic but this is a small price to pay for having just one LDF 450 coax going out of the shack. How well does my new antenna work? Well conditions are poor at the moment, but I can hear GB3ANG from Scotland OK on 2 and some beacons on 6m, so something is working. Now I shall just have to get a 4 mtr and 23cms transverters built.(a combined one ?) My 10GHz rig comes first though. Time. Where does it go?
That’s it for now.

Vy 73. Mike G3JKX.