Correction to my previous comment.
I didn't realize that the mini-flag
impedance is close to 50 ohms resistive
at all frequencies of interest.
Therefore, the 50 NF of any amplifier
is also the NF that applies when connected
to the loop.
The 50 ohm source impedance is a due to a physical
resistor with a physical temperature of 300K, therefore
the noise temperature of the system will never be less
than 300K. It is easy to find an amplifier that gives
a sensitivity within a few dB of a hypothetical
noiseless amplifier.
Rick N6RK
On 2/24/2021 4:53 PM, Richard (Rick) Karlquist wrote:
> 6. NF is source impedance dependent. Measuring the NF with
a 50 ohm source doesn't tell you anything about the effective
NF when terminated with the loop impedance (which is no where
near 50 ohms resistive.)
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