Re: Halloween Coiling and the FCC

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
>
> Hi All,
>
> The RF ground lead is the most likely source of excess radiation.
> For some reason folk believe that hammering in loads of huge
> earth stakes will automatically ensure a good ground for the coil,
> but if the ground lead has to travel from the coil base down three
> flights of stairs, through the garage and out to the yard, that
> doesn't really do anything for the coil, except to give it a
> reasonably good antenna.
>
> I would always advocate confining the E-field close to the coil,
> by using an artificial ground plane beneath the coil, if it can't
> be operated directly over the earth.

I heartily agree.... keep the RF path short (that includes the path from
topload to bottom of coil via ground...


> >
> To pick up a TC at 20 miles is really some feat!  At TC
> frequencies, the background RF noise against which the TC signal
> is received is quite high, so a fair bit of signal must be being
> radiated - rather more than we would expect from the coil and
> topload alone.

Depends... if the receiver was tuned to a suitable frequency up a ways, so
atmospheric noise is less, and where radiation resistance of the TC itself
is higher... A TC with a 15 foot ground wire might be a reasonably effective
radiator at 10-15 MHz....even if it is the 100th harmonic of the fundamental
(at 150kHz), the increased effectiveness of the antenna might help..






> Radiation is possible from
> a) the secondary resonances (up to a few Mhz); Ensure a short
> return path for the E-field back to the secondary base.
> b) from the primary resonances (up to 10 Mhz or so);  Keep primary
> wiring compact, use parallel line if long runs are needed.
> c) from the spark gap, which with its wiring forms a nice
> center fed dipole (up to several 10s of Mhz);  Fit ferrite beads.
> d) from arc discharges ie the resonance of the arc loop (up to
> VHF); Tricky.  Use short ground return path for discharges.
> e) from surface resonances of the topload while breaking
> out (VHF/UHF);  I don't know how much of a problem these could be,
> but some quite large current pulses seem to accompany leader
> formation, and they are of a duration short enough to excite the
> surface resonances of a toroid.  It would be nice to try to
> relate a measured spectrum to the dimensions of the topload.
> (should peak at a wavelength a little longer than the circumference
> of the toroid).

Indeed, a spectrum analyzer plot from a few hundred meters away would be an
interesting thing to look at... even if you just scanned a general coverage
receiver and plotted signal strength (AGC voltage?) it might show something
interesting...Anybody got a PCR1000 around?