[TCML] Oscilloscope methods for showing Ringdown
follies at ntlworld.com
Wed Mar 11 13:08:27 MST 2009
I have spent most of today trying to get a descent scope image of my coil's
ringdown. The primary charging curve did not present too much of a problem
using a 20 x 10 meg resistors in series, but the secondary has not worked
out well at all, despite what method I use.
I seem to get a very poor 'scope image full of interference and refusing to
sync' properly. I have tried manually syncing and even using a signal gen'
as an external trigger by trying all different frequencies. The only way to
view it has been to photograph it with a shutter speed that is quick enough
to hopefully grab one of the multiple images you get on the scope's screen.
I have shot 223 pictures today using various methods & over 200 are no
good!. I am only running the coil at 110volts (normally 240v 1kva) as it is
in my shed and space is very limited, but I still have multiple streamers,
or with a single breakout a strong 20 inch or so streamer to a grounded
wire. I did indeed find the best 'scope traces were obtained with breakout
to the grounded wire.
The four best examples can be seen here
http://www.flickr.com/photos/33962508@N03/?saved=1 There is some vertical
banding on these which I take to be the notches, but they are not clear
enough to say either way.
I have tried hanging probes near the coil ( I have used a x1, x10 and a
x100) . I have also done the same but with different lengths of wire on the
tips acting as an aerial. I then tried a coil around the secondary earth RF
earth by winding 30 or so turns around the earth lead and connecting the
probe across that. Also tried just connecting the probe tip and leaving the
coil open ended.
I then made a coil up of around 40 turns on a 2 inch former and used that as
an aerial instead, all without a great deal of success.
I know about Terry Fritz's antenna that he designed though I do want to
build one at this stage.
My single channel old analogue 'scope (Hameg HM103) has seen better days and
only has a small 7cm screen. I hate to blame this but I am wondering. Is it
really necessary to have a storage scope to get good ringdown traces ?
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