Frequency downconverters are required to test devices that operate in the range of microwave and mmwave. I have noticed that some companies use a signal chain that has an RF preamp, and some do not, opting to use an IF amplifier to combat the conversion loss of the mixer.
Double sideband mixing is used in these downconverters:
- Option 1: RF signal in → RF preamp → mixer → IF out
- Option 2: RF signal in → mixer → IF amp → IF out
In radio systems, I have never seen a down conversion block without an RF preamp. Is option 2 better?
The above links show one example of each.
My original post was edited, and perhaps my intent of the question may be misunderstood. To clarify, why would a preamp not be used, and specifially, not used in a downconverter to make noise figure measurements? I can't see why a downconverter to make NF measurements would not have an RF preamp. The major problem I see is when using a NF analyzer, where you calibrate with no device-under-test, the ENR gets buried by the mixer's high noise figure, casuing a bad calibration.