Wednesday, 5 December 2007

Pole Position

Today i had to do some shopping. A trip to the post office to collect the pressure sleeve UHF connectors i had ordered (finally got fed up of poor connections due to trying to solder braid to normal plugs) and to get animal feeds.

Now, i get my animal feed from a place called Hillam Feeds, a few miles away. So, with the car loaded up with sacks of feed, plastic containers etc, i headed back. As i passed a small building site, where some nice looking houses were going up, i noticed a young lad loading short scaffolding sections on a wagon. I slammed on the brakes, reversed back, and went over and asked who the scaffolder was. After explaining why i wanted scaffold poles, he went to talk to his gaffer. The gaffer then phoned the boss, and about five minutes later, told me "a tenner each", so with the help of the young lad i roped two 21ft galvanised scaffold poles onto the roofbars of my Fiesta, handed over £20 and started the careful drive home. Its only when carrying such a load that you realise how bumpy the roads are, and i had to go at 20mph to avoid the poles starting to bounce about. Luckily, the whole journey is over lightly used rural roads. So now im sorted for mast poles! All i need to do now is decide on the actual method of mounting and get the job done, and my 6m and 2m beams will be up in the air.

To that end, getting the pole attached to the house, i had a chat with the chaps at Brymar. Brymar are a satellite TV company, and i had to visit them anyway for a splitter and some sat coax and F connectors, for the wifes small works project of getting DTV into the kitchen. I had to get some self amalgamating tape as well as mines nearly run out, blimey thats expensive stuff, but its a real must have, its either that or Denso, and i dont think the XYL would like me using that! Im now wondering wether to go with the T & K brackets, which i think are a bit too far a stand off, or get some A frame brackets, that spread the load further out, and i think would be less pulled by the wind loading. If it can hold a 1m solid dish up in the wind, i think it can handle a couple of VHF beams!

Sunday, 2 December 2007

Theres a hole in my sealant

I finally got around to resizing the doublet from 102ft, as was for G5RV, to 88ft top section. I took the opertunity whilst scared stiff up the ladder to extend the lanyard considerably, taking the end of the antenna well clear of the buildings, and hopefully putting an end to any RFI problems triggering the neighbours security light.

As soon as i had it back in the air and went to test, disaster! nothing would tune right, and 20m (my favourite band) wouldnt work, giving an SWR greater than 6:1 if i ran high power. So, i thought, the line lengths are now wrong, so i went through the calculations and added 6ft of feeder to ensure no band was an odd quarterwave. No change. Hmm, strange. So i inspected all the joints and found one that was corroded. This being the point where the original G5RV matching section line joins the ladder line back to the balun. So, i cut the bad joint out. Still no better. Closer inspection showed one side of the ladder to have black copper oxide on it, hmm, its been wet. I cut it back, and back, and back. I cut out 4ft of line and it was still oxidized. Now, i had assumed that the water had got in at the bad joint, but now the oxidation was on a section that went vertical. So i lowered the whole antenna and had a look at the feedpoint. Nasty. Theres a little hole, right above the end on one of the lines, where the water can get in. And guess what - yes, thats the side thats corroded. All the way down the line.

So it looks like the poor tuning and performance is down to this water ingress. So i have to replace that section of line. Unfortunately i only have 13ft of line left, and the section if much longer, so unless i come up with a better way of routing the feeder, i'll have to buy another roll of ladderline.

All this has come at an awkward time, just as my friend Andy G7PZL is finally equiped for HF and wanted to do on air tests. I couldnt hear him at all, and hes only 25miles away or so. Im considering a Cobwebb antenna for the higher bands, this at least is coax fed. It all depends on what the XYL will let me have. Shes already not happy with me wanting to put two VHF beams up. It would still mean i would need antennas for 40m & 80m, maybe even topband 160m, but i could perhaps get away with a fan dipole for these and coax feed.

Either way, i need to finalise the antenna system before spring, for both HF and VHF, after which no further work can go into them except normal maintenance, likewise the shack. It has to become operational only, no engineering.