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Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
30/OCT/2008 I've rewound the primary from PVC proper insulated copper, around the secondary supports. It's further away now, which will affect the coupling and the behaviour, but should be a lot safer with less arcing, spitting and popping.
================================
29/OCT/2008 I've tried to make the coilforms as durable as possible -- with high-frequency coils, just a millimetres movement of one relative to the other can really change the performance, so I'm hoping I can engineer this one better.
Already the primary and secondary have flashed over (unsurprising; both enamelled copper wire), but that happened after first light, at least I was able to determine the resonant frequency first.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I've been trying to get some amps going here so I can basically do the same thing. I want to get a line driver going that has fairly significant power out, the only problem like you're seeing here is that the high SWR ratios and mismatches can cause large breakdowns in unexpected areas. You'll probably need to get some transparency film between the two coils. I'm also wondering about your loop area there, what are you using it for?
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
Peter, thanks for admiring the design quirks -- the separate oscillator board saves me from having to waste components and/or assembly time if I do a revision of the power board; I can just unplug the 4046 and transfer it to another board. My next design needs to allow for variable duty cycles, but for now I might just put a pulse-squisher on the input of the IXDD414.
Matt, it looks like transparency film won't cut it, the RF really loves insulators! I can feel where the enamel has been roughed by corona treatment, and the spot where it arced through on camera.
The trace forms part of the primary circuit, it seemed logical to have it follow the coilform (to complete the bottom turn) rather than cutting straight through underneath.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
There is provision under the secondary on the PCB for loading capacitors between sig/gnd. You can see if you look carefully at hfsec1.jpg and hfsec2.jpg. The actual tank circuit itself is on the driver PCB; I've omitted the drain capacitor for now -- there's just an LC flywheel network going to where the primary feed terminates at the edge of the board.
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Modest 10Mhz CW SSTC
