[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] Maximum Field



On 12/21/12 7:07 AM, Derek, Extreme Electronics wrote:
Jim,
     I agree with your assessment of the radiated energy, but if you
design a coil to give a high field without any mitigating sparks you
will radiate more  RF than usual.

     Even if you only radiate 0.01 % of say 5KW, that is enough to
interfere with radio communication in a large area, my warning was
purely to take this in mind when building such a coil.

     Luckily radios tend to use much higher frequencies than most of our
coils these days, so this is becoming less of an issue admittedly.

     Derek




0.01% is an amazingly high radiation efficiency...

Let's put some real numbers in...

Consider the TC as a 3 meter long antenna carrying an RMS current of 8 mA (this is about what you'd see in a 5kW big coil... 42 mH Lsec, 0.1uF CPri, 33 uH Lpri, etc.)

The standard far field equation for a "small" dipole (L<<lambda)..

This coil is at 84 kHz, so lambda (wavelength) is about 3.6 km..

field at distance r = I*L/4pi * 377 * 2pi/lambda * 1/r

so we have...
8E-3*3/2 * 377/3600 = 0.0013/r V/m
Let's assume you're at 1000 meter distance so the radiated field is 1.3uV/meter.

As a comparison, a 1 watt transmitter perfectly radiating, at the same 1km would have an electric field of 0.07 V/m

That is, your 5 kW coil produces an electric field at 1km that is the result of radiating about 20 microwatts.. (i.e. you're radiating 0.002%)

And in practical terms, atmospheric noise has a higher power density than your 5kW TC

AM broadcast stations have fairly decent radiation efficiencies.. well above 50%, and they produce fields of millivolts/meter.. KNX, a 50kW clear channel station some 50 miles away from my house produces a field of 15 mV/meter.




_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla