[AMRadio] Low Power AM?


sbjohnston at aol.com sbjohnston at aol.com
Sun Nov 23 22:07:40 EST 2008


Yes, of course you can reduce the loading and redip the tuning to get 
lower output.   You can also choose various settings of the loading 
capacitor to match various load impedances for higher output power.   
Another way to think of the loading adjustment is to imagine if varies 
how much of the load is coupled to the finals - how much the are 
"loaded"

If there was only one correct value for the loading capacitor, why 
would anyone ever spend the money for a variable?   (Cheap rigs don't - 
but they are stuck matching to a fixed output Z and degree of loading.

Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
-----------------------------------------------------
Radio is your best entertainment value.
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-----Original Message-----
From: rbethman <rbethman at comcast.net>
To: Discussion of AM Radio in the Amateur Service 
<amradio at mailman.qth.net>
Sent: Sun, 23 Nov 2008 5:57 pm
Subject: Re: [AMRadio] Low Power AM?









Jim,


I addressed this earlier with my statement that when doing this
"reduction of antenna loading" that THIS puts things into a 
NON-RESONANT
state.


The only way to do this AND stay resonant would be SOMETHING outside 
the
radio that DOES resonate.


The 35 ohm antenna you refer to is typical of certain antennas.  That 
is
WHY they have matching or loading devices that USUALLY go with=2
0them.


It is also why 1/2 wave dipoles have a VSWR RANGE where it works - AND
frequencies where it will NOT


Or am I wholly insane?


Bob - N0DGN


Jim Wilhite wrote:

> Ok I will ask the stupid question(s).  What is the purpose of a 
output
> (Pi, Balanced) network?  Is it not to transform the plate load
> impedance (everyone knows how to calculate this right?) to whatever
> the antenna presents to the output of the transmitter.  Is not the
> rated power calculated at 52 or 72 ohms?

>

> So if you have a final that is looking into 35 ohms (say a vertical
> antenna) and you dip the plate, what happens?  Do you see 50 ohms
> anywhere?  Is the system matched?  Just what is happening?  What is
> the efficiency and HARMONIC suppression at this particular setting?

>

> Anyone explain this to me?

>

> Jim/W5JO

>

>

>

>

>

>> I really did not say to maintain the dip with the load capacitor.

>>

>> When I tune the final of any Pi-network Tx I first set the dip with 
the

>> PLATE capacitor. Then I adjust the coupling with the LOAD capacitor.
>> And I

>> always recheck the dip with the PLATE capacitor after making any
>> adjustment

>> to the LOAD capacitor.

>>

>> And when I am done I DO RECHECK THE GRID DRIVE!

>

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--
Bob - NØDGN


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