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On 9/3/19 8:23 PM, hooverrl@xxxxxxxxxxxxxx wrote:
Subject: RE: Tesla Digest, Vol 142, Issue 1 RF Police
Try this link: https://www.pasternack.com/t-calculator-ratio-conv.aspx
Your 10,000 VA coil puts out +70 dBm signal
Try this link: https://www.pasternack.com/t-calculator-fspl.aspx
Pasternack calculator will tell you the signal loss for your resonating
frequency and distance to someone who may have a concern.
If 100 kHz transmits 1 mile away, you only lose 16.57 dB. Your signal will
still be quite strong.
If 1 MHz transmits 1 mile away, you lose 36.57 dB... so more loss the higher
the frequency, which means less interference at higher frequencies.
That's the "spreading loss" between isotropic antennas. The "capture
area" (effective aperture) of an isotropic antenna varies with
wavelength ( Ae = lambda^2/(4*pi) )
so as the frequency goes up, the "capture area" intercepting radiated
power goes down.
But the important thing is that a tesla coil is a really, really bad
antenna. You may be putting 10kW into the coil, but you're not
Also for low frequencies, you're in the near field (that is, more energy
is stored in the magnetic and electric fields than is radiated away).
At 100 kHz, the wavelength is 3km. So what you really need to do is
look at the magnetic and electric fields.
So, using RF propagation equations to predict tesla coil interference is
probably not all that useful.
Practical experience says that RFI from tesla coils is actually at
frequencies higher than the resonant frequency - it's radiated from
things like the wires to/from the spark gap, often at HF or VHF frequencies.
There's not a huge amount of power at those frequencies, but you DO have
an effective radiator.