[BC] Part 15 LPAM Questions?

[Robert Meuser]

The resistance through the device would be but one of the limiting factors.

R


Dana Puopolo wrote:

>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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>
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