It also has a couple of head to
tail 1N4148 diodes across the input for protection.

What those diodes will do is make horrible intermod if you've got a
transmitter anywhere nearby. Especially if it's wideband with no
filtering on the input.

Was wondering if a wideband preamp might have
a better noise figure if its input impedance is greater than
the antenna's.

Freaking around with impedance mismatches just to get a better noise
figure will only work for marketroids. Has no benefit and only
penalties in real life.

To quote H&H: "Big fallacy: don't try to improve things by adding a
resistor in series with a signal source to reach a region of minimum
NF. All you're doing is making the source noisier to make the
amplifier look better!"

Most RF amps spec noise figure for Z_in = 50 ohms and don't even try
marketroid stuff anymore.

Tim.