[AMPS] Need to pick your brain...

[Jon Ogden]

>The SWR/resonant freq. readings were taken with an MFJ-259 Antenna 
>Analyzer connected to the RF INPUT of the amp and the amp switched
>to the TRANSMIT mode, so the analyzer would 'see' the appropriate
>load.

This is a mistake.  

An amplifier other than one in class A operation needs to be "driven" 
into its active region.  As a result, the input impedance of the device 
varies substantially over the range of the drive cycle.  Look at it 
another way: the input impedance varies with the power applied.

Just keying the amp shows one nothing about the amps "true" input 
impedance.  If you want to see where the amp might truly be resonant, 
connect the amp into a dummy load and to a transceiver capable of out of 
ham band operation.  Then key up at different spots across the band.  
That's a better "quick" test.

The MFJ-259 puts out so little RF that there is no possible way that it 
can drive the tubes into their active region.  So your measurements are 
virtually meaningless.

Why did they look good on 80-20?  Well, perhaps dumb luck.  But as you go 
higher in frequency, it gets harder and harder to become "lucky."

73,

Jon
KE9NA


-------------------------------------
Jon Ogden
KE9NA

http://www.qsl.net/ke9na    <--- CHECK IT OUT!  It's been updated!!!!!


"A life lived in fear is a life half lived."


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm