[AMPS] Coil heating

[MM@plextek.co.uk (Mark Marsden)]

>
>An experience I had while messing with a 6m anode circuit: I wanted to
try a
>different coil size and fighting with 6mm (1/4") copper pipe was
getting
>tiresome. Allowing for skin effect, I figured that 6 x 1mm wires in
parallel
>(like litz wire) would give the same area for current flow and be much
>easier to handle.

> I made some twisted wire with a cordless drill and tried
>it. After about 20 secs. key down, huge plumes of smoke came out with
the
>exhaust air - when the coil was removed, the varnish had burned and all
>strands had started to fuse together.
>
>Maybe I'm missing something obvious, but I can't see why the losses
should
>have been much higher. The copper pipe will shift heat away more
easily, but
>even after prolonged use, the final pipe coil is not discoloured, so I
feel
>sure the difference was in actual dissipation.


*  RF current flows on the outer surface of the 6mm tube but 
can't flow on the surfaces of the 1mm wires on the inside of the
twisted bundle.

In fact it's confined to 6 thin lines on the outside, at 50MHz my 
guess is the Q drops about a factor of 3-4.

73 Mark G4AXX

>
>Steve
>

                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                                                                        
                   

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