[BC] Assistance With A PI Network Calculation

[K7qa@aol.com]

In a message dated 2/24/2007 1:02:00 PM Pacific Standard Time,  
tonne at comcast.net writes:

Tom  wrote:

>  Wonder if someone could give me the  approximate
> values of the input and output capacitors for the PI  network
> at 3.8 MHz?  The 1625s will have about 700 volts on the  
> plates with 300 MA which is a plate load of 2333 ohms.  
>  The output of the PI network will of course feed 50  ohms.



Remember that for ham transmitters, you dont always have a perfect 50 ohm  
load to work into, so you need more adjustable range. A pi section is  popularly 
used in most all ham rigs not only because it can match a larger span  of 
load impedances and still transfer the PA power into the line.....but also  
because the lagging pi network is a good low pass filter for harmonic  attenuation 
and lends itself to multiband operation better and more easily.  The series 
coil is tapped with a band switch and full range variable capacitors  can be 
used on each of the shunt legs to handle frequencies from 80 thru 10  meters 
using the same components.
For only 80 meter operation, that wont matter ofcourse. You'll probably  need 
about 300 pf on the input side for resonating and 1000 pf for the output or  
loading control.
 
tm
 
tm
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