So I have just taken delivery of a very gently used Tokyo Hy-Power HF linear amplifier.
The previous owner (retired communications and instrumentation technician for a large, multi-national organisation) replaced both fans with ultra low noise “Arctic” fluid bearing units. These are installed in 2 speed via voltage regulation manner: Low speed during stand-by (RX) and High speed during TX. Continue reading
RF Weld – Click to zoom
In the process of testing out my 80m coil this morning to load up my 40m vertical, I pushed 400w AM up the antenna and the ACOM went into alarm, telling me the SWR had gone too high.
Upon investigation, I noticed that just at the top of the coil, as the D10 comms wire kinked around some insulation tape and started its travels vertically, the wire had welded apart.
I made a repair using extra heavy gauge copper to take the high high current and all seems well again.
RF Weld – Click to zoom
The M0XXT Double Xray Firm had one of our outings again last weekend with myself, Tim (M0URX) and James (YOMsoft author). We built our biggest vertical yet, a loaded quarter-wave for 80 meters. Click the picture to compare Tim and I against its size. Awesome! 21 foot (6 meter) scaffold pole with 40 feet (12 meters) of SpiderBeam pole above. We’re getting an 18 meter version of this which should be great fun.
For speed of assembly on the day, we used 4 very thin strands of insulated copper wire out of a three-pair (6 way) telephone reel for the elevated radials. They’re very thin but would do the job of allowing us to raise this baby up in the air 6 meters.
The radials ended up at ground level, wrapped around galvanised tent pegs. Without realising it, we were trusting the insulation coating of the wire itself to keep the radials from being grounded. Actually, we never really thought about the consequences! Anyway, a 100w squirt proved most efficient and we achieved a 2:1 SWR curve from 3.625 to 3.750. We needed to shorten it a few more inches, however before we took it down again, I thought it prudent to fire 400w up it to make sure nothing broke down. Thump; I stuck a good carrier from the ACOM 2000 down the pipe and “pop”. The SWR pinged up to over 3:1. What had happened?
The insulation on every single tent peg had broken down in an instant and melted through to convert our careful elevated radial system into a grounded system in a flash.