Hi,
On 2022-07-07 07:22, Bob kb8tq via time-nuts wrote:
Hi
On Jul 6, 2022, at 1:53 PM, Richard Karlquist via time-nuts
<[email protected]> wrote:
The 2N5179 has high base spreading resistance (decreases isolation).
As does sticking a resistor (even a small one) in series with the base …. Yes,
inductance
is even worse.
For “best isolation” in a cascode you very much want the base of the common base
stage nailed to ground. Typically “lower” Ft transistors with a decent base
structure
are the best choice for the common base stage. Both stages benefit from low 1/F
noise
in the audio range if this is for a phase noise test set. This is why people
use what would
normally be considered “audio” transistors ….
The NIST isolation amplifiers does exactly this. Looking for Fred Walls
in the NIST T&F archive usually makes me find the article quick.
Cheers,
Magnus
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