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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