[BC] Part 15 LPAM Questions?

[Dana Puopolo]

Yep.

Let's be generous and round that up to .1 ohm....after all, I'm running my
Part 15 at 1690 kHz.

With two ohms of ground losses (the average for a 1/4 wavelength 120 radial
buried ground system), 95% of the RF will be dissipated as heat.
(.1/2=.05). Assuming a final efficency of 80% and 100 milliwatts (.1 watt)
input power; 80 milliwatt output power), 4 milliwatts of RF energy will be
radiated!

Remember, this number also assumes a ground system better then 99% of the Part
15's have.

BUT..that might not be so bad....

Look at the efficency for the (ported) EV Sentry 100A loudspeaker. With 1 watt
input power, this fairly efficient speaker puts out but 2 mW of acoustic
energy.  I used to own a pair of these, and they play quite loud run at 1
watt.

-D



------ Original Message ------
Received: Sun, 10 Sep 2006 10:13:44 PM EDT
From: "Jim Tonne" <tonne at comcast.net>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Subject: Re: [BC] Part 15 LPAM Questions?


I just looked up the R and jX values of a 10 foot tower
over excellent ground at 1500 kHz.  The radiation
resistance is near 0.07 ohms and reactance is about
negative (capacitive) 3100 ohms.

To match that to 50 ohms would take an L-network with
an input shunt C of about .055 uF followed by a series
inductor with about 335 uH.  At a power level of  *one* 
watt there would be about 4 amps going through the 
capacitor and 11.7 kilovolts across the inductor.

Not real good!    

- JimT

Hope my rithmetic was OK.


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