Tom Rauch wrote:
>
>While parallel networks are often just as good, T networks are really a
>very poor choice. They are a system begging for less-than- obtainable
>IMD or efficiency.
>
>You have two basic flavors of T networks, and while one type is a low-
>pass and will reduce harmonics appearing back at the exciter none of
>them do a good job of ensuring that cathode doesn't pump around with
>harmonic energy.
>
Amplifiers for 50 and 144MHz often use what look like L-C-L T-networks
because the tube's own input capacitance makes it difficult to design a
pi-network with sensible component values.
What you actually have is a step-up L-network from 50 ohms, back-to-back
with a step-down Pi into the cathode. C2 of the Pi-network is the tube's
input capacitance, so the situation isn't quite so bad as it looks on
the schematic.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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