This does not cover the question of matching OUTSIDE the limits of the
impedance "SPECIFIED" 50 to 75 ohm antenna system.
This isn't a TRICK question!
I said it very succinctly. You WILL need SOMETHING outside the radio to
achieve resonance. Otherwise your VSWR is going to be WAY out of whack
and plate current/plate power displacement WILL be way out of parameters.
Hence antenna tuners, antenna matching devices at their base, and etc.
Bob N0DGN
[EMAIL PROTECTED] wrote:
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
[EMAIL PROTECTED]
http://www.wd8das.net/
-----------------------------------------------------
Radio is your best entertainment value.
-----------------------------------------------------
-----Original Message-----
From: rbethman <[EMAIL PROTECTED]>
To: Discussion of AM Radio in the Amateur Service
<[email protected]>
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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