[BC] Part 15 LPAM Questions?

[Dana Puopolo]

Like I said, an emitter or source follower would match to the very low
radiation resistance of the short antenna - and would also be able to handle
the large capacitive reactance of the short antenna.

Though it has a power gain of about .7, it's loss would still be much less
then the loss of a large loading coil.

Of course, the most important thing is as good a ground as possible. Note that
the FCC specifies the length of the "ground lead" - NOT  the length of the
ground (system) itself.

I'd go for an expanded screen and/or a bunch of radials.

-D

------ Original Message ------
Received: Sun, 10 Sep 2006 11:38:14 AM EDT
From: Robert Meuser <Robertm at broadcast.net>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Subject: Re: [BC] Part 15 LPAM Questions?

While what you wrote is absolutely true, the reactance is the key 
problem as the required loading coil will have significant resistance 
compared to the resistances you mentioned. While ground losses are also 
a problem, the resistance of a practical loading coil is the big 
sticking point.

R


Richard Fry wrote:

>> It is the extremely high reactance that is the problem.
>
> ___________
>
> The high reactance is a problem, but even when it is canceled using an 
> inductance at the feedpoint, the radiation resistance of a 3-meter 
> conductor -- when the 3 meters includes the conducting path to an r-f 
> ground buried in the earth -- is barely 1/10 of an ohm even in the 
> X-band.
>
> The r-f resistance in the ground connection of a typical Part 15 setup 
> can be tens of ohms.  Antenna system efficiency is the ratio of the 
> radiation resistance to the total of all resistances in the antenna 
> system, so even a resonant Part 15 antenna system can have 
> efficiencies of less than 1%, and many/most of the FCC-compliant ones 
> probably do.
>
> RF
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