[Amps] Pi vs Pi-L

[Bill L. Fuqua]

-----Original Message-----

The ubiquitous t-network tuner with series capacitors and a shunt inductor (like the MFJs) is a high-pass filter, so it won't help a bit. 
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Not quite right. As a counter example, think of a pi network. It should be a low pass filter, right? But is not.  If you tune a PI network to a frequency higher than the signal frequency you get practically no output.  Same is true with a T network. If it is tuned to a frequency lower than the signal's the output drops. This is because the chosen component values are for impedance matching rather than simply a low pass or high pass filter. You have over looked resonance. Yes, in the T more harmonic power will pass than in the Pi. But, not as much as you may imagine.  Particularly when you are matching very different impedances. 

    Try it. Tune your amplifier to 30 meters into a dummy load and then switch your driver to 40 meters.  This test is only valid if you have a untuned input circuit.  Do you get an output? It should be a low pass filter and 40 meters is a lower frequency than 30 meters.  Same is true with the T matching network. 
   
73
Bill wa4lav
 
ot quite right. As a counter example, think of a pi network. It should be a low pass filter, right? But is not.  If you tune a PI network to a frequency higher than the signal frequency you get practically no output.  Same is true with a T network. If it is tuned to a frequency lower than the signal's the output drops. This is because the chosen component values are for impedance matching rather than simply a low pass or high pass filter. You have over looked resonance. Yes, in the T more harmonic power will pass than in the Pi. But, not as much as you may imagine.  Particularly when you are matching very different impedances. 

    Try it. Tune your amplifier to 30 meters into a dummy load and then switch your driver t