I have posted before about rebuilding a ham radios station at the Gilwell Park (GP) Scout Activity centre. The only remaining part of the previous station is a damaged 3 element triband yagi on the 30m commercial tower. This hasn’t been used for two or three years and with the help of employees at Gilwell I am working towards getting the antenna changed by the tower owner.

One problem came to the fore though. If the rotator needed changing as well as the yagi then the riggers would have a much bigger job to do. My task for the weekend was to work out how to reattach the cable dangling down the tower to the rotator control box and see if the antenna would turn.

The control box had a bit of paper on the underside allegedly showing the connections to the main cable run, so on Saturday I popped over to GP and wired the whole thing up from outside the tower compound. The antenna turned but the indicator needle didn’t move at all. I suspected that pot in the rotator head had been damaged, but took the rotator controller home to make sure it was working properly.

Whilst the control box was in bits I discovered a flat spot on the positioning pot in the rotator control box, but luckily I had a similar pot in my junk box so was able to swap it out. I had hoped this was the cause of the non moving needle and it was good to fix but certainly wasn't the core problem!

I went back to GP on Sunday morning to test my handiwork but as per Saturday the antenna was still moving but the indicator needle was remained static. Time for some trouble shooting.

Foolishly, I had used the diagram taped to the base of the control box showing the pin out of the control box, the colours of an intermediate jumper cable and how these both linked to the colours of the cables on the tower to the rotator motor and when things weren't working I realised I shouldn't have been so trusting. I decided that I had to work out role of each cable from scratch. This was made easier as the motor cables were clearly working and only 5 wires were required overall. That said, there were eight wires in the cable to the rotator head! On a couple of control box outputs the thin cables in the multi way jumper cable were being run in parallel to increase the current handling capability, but when I traced these through to the control box it became evident that several poles were being cross wired by the jumper. I thought I had found the problem but when I paired wires up correctly this didn't sort things out. So where now?

Out came the DVM and I started to identify the role of the cables
running down the tower. Once I had eliminated the motor power cables it was quite easy to discover which were the positioning pot in the rotator head. It was a great relief when I saw the resistance changing in this pair as I turned the antenna - the pot in the head was OK, meaning the problem was at ground level and therefore fixable. Phew.

A quick comparison with the erroneous wiring diagram suggested that the original installer had actually wired the jumper cable to the main run like for like i.e. red to red, white to white etc, except of one pair where there had to be a mismatch. As I had already identified the motor pair and two of the control leads I knew that the all the remaining wires on the tower were either unused or the remaining "lost" connection. So, I wired them all in parallel and hey ho the rotator indicator started to turn with the antenna. It was a simple process of elimination to find out which of my parallel set was the real deal.

So overall we have a result as shown in the video below. The antenna turns and the control box follows. I took a look at the main co-ax run to the antenna and the copper is bright - as new. This means we probably don't have to change that run unless I can find enough heliax. More good news!

I will try to get back to GP soon with my soldering iron and VNA. If I put a PL259 on the remaining co-ax and sweep the antenna we will have an idea of performance. It may be that a 2.5 element yagi is usable and I think that this will be a bonus for JOTA in a few weeks time.

New toy alert! I have recently picked up an elecraft band decoder to use with my remote station. Elecraft got the kit over to me quickly and it is now assembled and ready to go.

This bit of kit means that I can use the TS-480 to switch antennas at my eventual remote QTH. Icom and Yaesu radios are better at handling the band outputs than Kenwoods so the options for the 480 are quite limited but the guys on the TS-480 yahoo group say this one works a treat. I'll give it a go and see.... 

I had an interesting discussion with Frank, M0AEU about the Gilwell Park radio station this week and have been playing around trying to design a station that will be useful for the Scouts and possibly double up as a contest site in the Scout close season. The rules for the station are simple – no wires in places where the scouts can get at them!

That doesn’t preclude temporary antennas for contests. I have done a screen grab of the site from Google earth and marked up some preliminary ideas.

The site has changed a bit from when this image was taken and the building outlined in blue has been removed and replaced with another one that is a different shape. The radio shack will be in the new building at the spot marked with the arrow. My initial thoughts are to have the following permanent antennas:
  
There is a commercial tower on site, about 90ft tall marked T1. My current plan is to have an HF triband yagi, plus 6m yagi on this tower. This tower would also have a side arm with halyard supporting inverted V dipoles (160, 80 and 40m, marked in purple ends >20ft above the ground). These are oriented east-west at the moment, but I am unsure of the effect of the metal roof blow them. The side arm could also hold a V/UHF vertical.

The second tower, T2, is a 40ft crank up mast with a decent sized stub mast on top. This will be the VHF mast supporting yagis for 2m and 70cm. I also have a butternut HF2V vertical antenna for 160/80/40 that could be hidden in the trees at “Bnut” to provide some low angle radiation on those bands.

This should be a fairly straightforward install as I have most of the kit to do this already.
  
The remaining markings are for temporary antennas that would be set up for contest use. The two green circles (rough scale to include radials) could be full size verticals for 40 and 80m. The yellow dashed lines are along thick hedgerows and could be used for reversible beverage antennas. The 800ft length would be to central America/Japan which makes sense, but I am not sure whether it is worth the effort to install a 400ft one running N/S. Is it worth having an Africa beverage? As you can see form the picture there doesn’t seem to be an easy option to install a North America beverage unless it runs across open land. 

So, play fantasy radio station with me. What would you do on this site and why?

I have blogged several times about my involvment with the Scout radio station at Gilwell Park, GB2GP. The shack was lost 2 years ago and the HF yagi took a beating over the winter

I happened to go over there this wekeend as a group of radio scouts were using GB2GP from a tent with a dipole in the trees. I had a long discussion with a couple of the leading lights at Gilwell and it looks like a rebuild of the radio station is on the cards. I have offered my services and look forwards to getting stuck in and producing a decent station for all of the Scouts that visit the site.