From: "Terrell W. Fritz"
Date: Sat, 03 Feb 2001 15:25:44 -0700
Subject: Re: [TSSP] 50 ohm Generator hookup
Hi Paul, At 08:08 AM 2/3/2001 +0000, you wrote: > >You may find now that with the new generator the variability of your >coil's Q may become troublesome. Do you have any other coils >available for testing? I have my small coil. It is about 1180 turns #24 on a 4.25 inch form 26.125 inches long. >Smaller, non-sonotube, perhaps? Measuring Q >indoors is a real problem since the resulting Q depends so much on >how much energy is absorbed in walls, ceiling and floor. For a test >setup capable of doing justice to your new generator you might want >to consider switching to a smaller coil on a low-loss former, one >which is small enough to completely enclose in shielding so that its >Q will be high, stable, and possibly even predictable. > >As regards the base drive, the method you've been using seems fine, >although it's better if the current shunt, etc is moved to the coil >base end of the feeder. Something like the arrangement shown in >http://www.abelian.demon.co.uk/tssp/tmp/basedrive.gif >might have some advantage. I tend to prefer this so that I can get >both V and I samples referenced to ground, although the thing has >to be calibrated by replacing the secondary coil with a known >resistor. The coupling transformer (flyback ferrite) is a step-down >ratio to drop the incoming 50 ohms down to something nearer 1 ohm, >say 5:1 or 10:1 turns ratio. The whole gubbins can be boxed for >stability and shielding, and placed under or near the coil. Great idea! I just whipped mine up: http://hot-streamer.com/temp/box.jpg http://hot-streamer.com/temp/box2.jpg The ferrite transformer is 10 litz turns on the secondary. I sort of lost track of the turns on the primary but I don't think that matters. The resistor is a 1 ohm 1 watt surface mount. You had the ground of the input isolated in the drawing. I didn't have any isolated BNC connectors but maybe that does not matter? The signal generator's output is floating given some capacitance to ground. I'll test it out as see how it works. Again thanks for the great idea! Cheers, Terry > >Regards, >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.