On 29th December I attempted to have a go in the World Wide Iron Ham contest. I wasn’t planning on a big entry but was just going to run for a couple of hours to have a break from the Christmas festivities.
I fired everything up as usual but when I started transmitting, my Acom 1000 displayed an ARC FAULT error and cut out. Nothing I could do would make it work properly so I gave up, went downstairs and had a mince pie, a glass of beer and watched a James Bond film (Goldfinger).
The next day I started investigating the cause of the problem. My first thought was that there was a fault with my aerial so I connected my VNA and checked it – It all measured OK so I looked at the amplifier itself. I ruled this out by running it into my 10m/12m vertical and my 40m delta loop where it worked perfectly. I also fired the amplifier up into a dummy load with no problems indicated.
So it’s an aerial fault. But the aerial checks out OK with the analyser so I thought perhaps the balun was breaking down at high power. I knew the aerial seemed to be performing correctly as I’d used the radio without the amplifier and noticed no problems, working down to Argentina and Brazil on 10m and lots of Europeans on 20m and 15m.
Last weekend on Saturday morning I lowered the mast for the first time in months, disconnected the coax from the balun and connected a dummy load. I fired the amplifier up and again, it tripped out so the problem wasn’t the aerial or the balun, it only left the coax. My VNA came out again and the coax all seemed to be OK.
At this point I took a closer look at the PL259 fitted to the coax at the top of the mast and this is what I saw.
This connector was originally fitted when my Alimast went up and the only protection it has had against the elements was the rubber boot supplied with the MA5B. It’s clearly suffered from some water ingress and that combined with high power data at a high duty cycle is what’s caused it to break down.
I chopped the coax back by six inches, fitted a new compression type PL259 connector and tested with the dummy load and the amplifier on. It worked perfectly so I taped it all up to protect against the weather and raised the mast back up. It had a thorough test in the ARRL RTTY Roundup on Sunday where I worked nearly 500 stations using the amplifier and the hexbeam with no problems.
One important thing I’ve learned apart from making sure that connectors are properly insulated and that’s that long handled garden secateurs are absolutely fantastic at cutting through RG213 coax! I’ve also been reminded that I utterly hate and detest PL259 connectors.