Mauri says:
>Often, a too good noise figure has a negative impact on the dynamic
>range and intercept point while an optimal IP could shift the dynamic
>range out of the useful range leading to a bad ground floor noise.
Spurious Free Dynamic Range is 2/3 of the difference between noise floor and
input intercept point (usually the 3rd order input intercept point) So for
any receiver, the dynamic range can be moved by using an attenuator, but
remains a constant number of dB. Having a low noise figure leads to the
intercept point being lower for a given dynamic range, but an attentuator of
the correct value restores the intercept and moves the dynamic range up. The
big question is: What dynamic range do you actually need?
This isn't easy to answer; it needs a lot of measurements. So far, the few
I've done suggest about 95 to 100dB, with a lower start point variable
between a 10dB noise factor and a 30dB noise factor. That's an intercept
point of around +15 to +20dBm, with the higher value desirable for CW. Phase
noise then needs to be at least -144dBc/Hz at around 5 - 10kHz, (to handle
multiple interferers) and spurs need to be minus 100dBc.
That's pretty exacting.
73
Peter G3RZP
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