[BC] Part 15 LPAM Questions?

[Robert Meuser]

I will not double check your numbers, but you left out the loading coil. 
The loading coil is usually the biggest loss in the equation.

R


Dana Puopolo wrote:

>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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