"This method has been used in the real world for many years, and it is
still
being used. Better ways?


Several.

Long story short, the power-to-voltage ratio of a signal is always
higher than the power-to-voltage ratio of noise. Most RF front ends
are voltage amps. But a -power- amp on the left can dig the signal out
of the noise on the order of 2-4dB, sometimes more. I like using a
common-base for the 1st RF, but you can re-bias a common emitter and
make pretty good improvements. And, as I stated before, a low input
impedance will reduce or eliminate the impedance transformation prior
to amplification.


The objective is not low gain but low input impedance. Closer to the
impedance of the feed, to keep the first impedance transformation as
small as possible. With a common emitter, the only way to do that is
by reducing the gain. And just at the first RF stage, not necessarily
everything else in front of the first mixer.



As long as we are on that subject, an RF stage isn't even needed at
frequencies below 30MHz. As an example, you can use a Mini-Circuits SRA-3
doubly balanced diode ring mixer, that has only 4.77dB conversion loss at
11M. You also have approximately 35dB of port to port isolation.


You can do better with discretes from Radio Shaft, which is really sad
when you realize that those are their lab numbers. The only advantage
I've seen to Mini-Circuits is the size. For performance, their stuff
sucks.

From the above statement, I can tell that you have very little experience
with doubly balanced mixers, especially the ones from Mini-Circuits. The
LAVI-XXX series of mixers have IP3s in the +33 to +40dBm range. The only
type of discrete mixer that can even come near this type of performance is
something that uses either a quad JFET ring, a quad CATV bipolar ring, or a
dual power FET type that uses something like the Siliconix VN66. Your
typical balanced dual JFET mixer, as used in some of the Yaesu and Icom
transceivers will achieve IP3s in the +10 to +15dBm range, which isn't bad.
This is without having the preamp switched in.
Now, to even be able to measure that type of performance, you need to have
all of your RF sources very clean. This means at least -65dBc for all RF
signals. Special attention must be paid to the 6th and 9th harmonics of the
LO, as these artifacts can cause poor return loss of the I.F. port and also,
2nd order IMD measurements can be degraded.
The test setup must have an intermodulation free dynamic range of at least
10dB better than the device you will be testing. This includes connectors,
attenuators used for isolation, etc. Attenuators with transverse heat sink
fins have the best IMD characteristics.

The only
advantage that an RF amplifier would provide in this situation is
minimizing
1st LO radiation through the antenna port of the radio.


It also serves as a buffer to the mixer, which is essential for
reducing mixer IMD. The RF amp is generally a good idea.

The RF amp will not reduce IMD..........it will actually degrade the IMD
performance of the mixer by the amount of gain that the RF amp provides. It
is very easy to see this if you are making IP3 measurements on a mixer. Add
10dB of gain ahead of that mixer, and IP3 degrades by 10dB.