LF: Advisory / Warning

[Andy Talbot <andy.g4jnt@gmail.com>]

Thought I'd better warn QRO LF ops about this - something that had never occured to me before, and could be nasty.

 

I'm laying floor panels in my loft space, and this involves rerouting some of the upstairs lighting wiring - drilling holes and feeding the wire though rather than it laying on top of joists where the flooring will sit.  Anyway, there I was, was happily threading twin-and-earth cable by torchlight (*) when I suddenly got a nasty RF burn holding one end of a piece

 

The 500kHz WSPR beacon is running, and the bit I was holding was isolated from the house main earth wire.  The Tee antena runs outside over the roof, only 3m or so away from where I was working.   So more than enough pickup with me and a bit of wire forming a dipole in the near field of 4kV at 500kHz

 

Now, bearing in mind the burnt ATU cabin of a few months ago, it made me think...

Large bits of bare isolated wire or metal in roof spaces where LF antennas pass over could be risky.   They could pick up enough voltage to spark - and if there's paper/ wood / plastic at the sparking point, an RF spark that always seems to turn into an arc, is very hot.

 

Just a thought.

 

(*) and BTW, there is a very strong argument for not having your roofspace light on the same circuit as your normal upstaris lighting

 

Andy

www.g4jnt.com