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Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
Hi,
I built steve wards sstc5 mini and eventually got around to boxing it up in a computer psu supply box (metal). I am having issues with the antenna though (the secondary is on top of the psu ) , I have cut it really short about an inch and a half and its sticking outside of the box. If its raised more or less then about 1/4" the coil doesn't run constant or at all.
I lengthened the antenna to about 4in and put it perpendicular off the box and it seems to work well and produce even larger discharges then before but still is inconsistent sometimes...
I found that by pinching it with my fingers i can make the coil produce the largest possible by the setup and the most constant.
Any advice on how or where the antenna should go for best results, im sure someone has had this experience too
thanks
Edit:what about this option... i dont think i would have to change my setup except for the ferrite core "Another method is obtaining feedback using a small current-transformer on the secondary coil. This is constructed by wrapping around 50 turns of wire on a small ferrite core with the secondary wire going through this ring on the ground side. Care must be taking to ensure the right phasing, which is simply done by reversing the direction of the secondary wire if the phasing is wrong. I find this to be more reliable than the antenna, and removes the need for a fragile wire sticking out of the driver. Thus I have employed the use of secondary current feedback. Likewise, schottky diodes clamp the output. The output of the current transformer is fed through two logic inverters (74HC14 or similar) which cleans up the signal to the Mosfet driver."http://www.loneoceans.com/labs/sstc2/
#Design
since im new to SSTC i would need some help with this though :(
The metal box acts as a faraday cage blocking the feedback signal, and it also acts as a capacitor in parallel with the antenna, so if you can get it farther away from the box you'll have better results. The reason why touching the antenna makes it work well is that your body is a huge capacitively coupled antenna to the topload.
You can use a CT feedback as well but keep in mind that you'll have trouble running CW (if you do this at all) unless you provide an enable pin ping to start oscillation manually.
The antenna can be a bit tricky, but I found that I get best results with the antenna is sticking parallel from the secondary coil, i.e. perpendicular from the floor. I think 4 to 5 inches is a good length for small to medium sized coils. Just make sure it's far enough away so it doesn't get hit by the sparks, but near enough so it gets a nice strong signal. You can play around with a wire stuck to an oscilloscope with your coil driven at the base by a signal generator to get a feel of how the antenna picks up signal, but be sure to use some sort of insulating rod to hold up the antenna :)
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
I used a small acryllic tube, regular wire going out through the metal shielded driver and the tube makes it much easier to adjust the coupling by pulling it down or pushing it up.
I adjusted it for maximum spark output and minimum corona on antenna tip ;)
You can see here how I positioned the antenna in this full-bridge sstc5 clone:
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SSTC antenna question
