At 9/16/2018 07:39 AM, you wrote:
As you saw, you can improve the
input match somewhat by tuning the input
away from the point of lowest noise figure.? At the point of best
match, the
NF will be above 1 dB.? For repeater service when the preamp is
following
filtering, this is often a better trade-off - I'll take the improved
match
over the fraction of a dB of noise figure any
day.
If the tradeoff of NF is small (0.2-0.3 dB) I'd agree.? The NF spec
on the ARR 440 preamp is 0.5 dB, so if it's meeting spec w/o tuning I
wouldn't be so keen on degrading the NF by half a dB just for a better
input return loss.? I once had a preamp in service that had an input
RL of only ~3 dB & in service it performed identically to an
identical model that had much better RL.? No doubt the duplexer got
detuned a bit by the poor RL, but in this case it wasn't enough to affect
actual on-air performance.? My point is that a preamp with poor RL
can still perform well, whereas a preamp with poor NF will not.
Certainly the optimal solution would be good input RL without degrading
the NF.? In tests I've conducted on the Mini-Circuits PGA-103 I was
able to increase the input RL to > 25 dB over a 25 MHz bandwidth with
corresponding NF degradation of 0.15 dB.? IMO this is quite
acceptable.
Bob NO6B
