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Re: ground & tuning

At 03:25 PM 01/09/2000 +0200, you wrote:
snip...
>What I wanted to ask is how can I measure, for purpose of tuning the coil, 
>with just a DMM (don't have scope or other stuff) if the primary&secondary
>are in tune? 
>
>I got the impression that when the coil is tuned right, the current flow
>to RF ground will be at maximum. So would it be possible to hook up the
>DMM to the ground without damage? (in what range would the amps be? 100A?)
>Like
>
>---------+---0.5 Ohm--------------------+------> GND
>base     |                  _________   |
>         +--100kOhm---|>|---| mA(DC)|---+
>                      D1    ---------
>                  (RF diode)
>where the low-ohm resistor has high wattage. Could this do? Or would the
>DMM heat and pop?
>
>thanks!
>Jan
>

Hi Jan,

The peak current in the secondary ground will be around 5 amps.  The RMS
current will be around 150mA.

The problem is the frequency and the available voltage.  The meter,
resistors, diode, etc. my act very differently than they do at DC.  The
resistors may have inductance and such that could do odd things that could
damage the meter.  Also there is about 250000 volts available in this
circuit.  If something goes wrong, the meter would be at very high risk.

I would not connect a digital meter in this circuit.  Try some cheap and
expendable meter.  Many people will simply put a light bulb in ground path
and go by the brightness.

The best way is to simply tune to get the biggest arcs...

Cheers,

	Terry
References: