A coil tuning aid

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "J. B. Weazle McCreath by way of Terry Fritz <twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>


Hello Coilers,

Most of us tune our coils by watching for the longest streamers, but not
being satisfied with that, I set out to find a way of actually measuring
the output.  I reasoned that by measuring the current in the ground lead
of the secondary, I could use that to optimise the tuning.

What I constructed was a radio frequency current transformer, by winding
16 turns of teflon insulated hookup wire onto an Amidon T-200-2 toroid
core, and passing the secondary ground wire through the toroid hole to
yield a turns ratio of 1:16 which gives a nice level of signal.

A length of RG-58U coaxial cable brings the sensed signal to a point far
removed from the coil where it is terminated with a 50 ohm, 5 watt, non-
inductive resistor.  I use my lab VTVM and its RF probe to measure the
voltage developed across the resistor.

It's interesting to watch the meter readings as I run the power variac
up and down, showing that it does indead indicate a relative output of
the coil.  By watching the meter, I can also vary the air flow through
my hyperbaric gap, and set the blower speed for maximum output at any
given power setting of the coil.

The meter readings are directly related to streamer length, showing me
that I now have an accurate way of tuning and tweaking my coil for the
maximum performance.  

73, Weazle, VE3EAR/VE3WZL
G-1#1214

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  http://www.hurontel.on.ca/~weazle