[AMRadio] Low Power AM?

rbethman rbethman at comcast.net
Sun Nov 23 18:57:49 EST 2008


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

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 them.

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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