[BC] Part 15 LPAM Questions?

[Dana Puopolo]

Yep.

A six foot diameter top load would be a big help here.
Actually, if you look here:  www.w8ji.com , you'll see that at 1500, a 10 foot
radiator is about 5.5 electrical degrees, and has a characteristic resistance
of about .22 ohms (with a couple thousand + ohms of cap reactance). So, our
numbers are off by about 1/2.

-D





------ Original Message ------
Received: Mon, 11 Sep 2006 07:28:29 AM EDT
From: "Richard Fry" <rfry at adams.net>
To: "Broadcast List" <broadcast at radiolists.net>
Subject: [BC] Part 15 LPAM Questions?

>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. (0.1/2=.05).

But in order for a tx to apply significant power to 3 meter radiator in the
MW band, the high input reactance of the radiator needs to be ~canceled.
This takes a coil, and that coil has loss.  And the coil loss probably will
be several times greater than the 2-ohm ground loss in your example.  If
that loss is, say 8 ohms, then the radiation efficiency of this system
drops to  0.1/10.1, or about 1%.

And as you point out, the ground resistance in a typical Part 15 AM setup
is a lot higher than 2 ohms.  It may be as much as 20 or 30 ohms, which
puts antenna system efficiency even lower than that 1%.

RF 

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