Why some receiver blocks are called superheterodyne?

Superheterodyne is a system level way of making a receiver or transmitter. It allows some analog (and digital) signal processing at lower frequencies where these can be done more cheaply. It also puts the system gain at different frequencies so that any coupling from output to input does not cause oscilllations.

Noise figure is the ratio of SNR in to SNR out.

Armistrong -the father of the RF communications-
is the invetor of the hetrodyne and super-hetrodyne recievers
also the regenerative receivers is invented by him
it was just a historical point of view about your topic
Actually the difference between hytrodyne and supre hetrodyne recivers is the number of frequency translation stages used
In the hetroudyne one , we are using only one frequency translation stage
but in the suprehetrodyne, we are using more than one (may be 2 or 3)
every topology has its adv. and disadv. from the system level and system spec point of view
I think that you can find many papers telling you more about this

At room temperature the Noise Figure of a receiver (NF – in dB) is function of Required RX Sensitivity (in dBm), Receive Bandwidth (BW – in Hz), and Signal to Noise Ratio at the input of demodulator (SNR – in dB).
Here is the formula:
NF = 174 + RXsensitivity –10*log(BW) - SNR

refer to "Communication Systems" by Simon Haykin.

One further historical note. The superheterodyne was patented in England, France, and Germany years before Major Armstrong made it into hardware. Armstrong was a glory hound and took advantage of every opportunity for publicity.

The French unit of ITT had a working microwave RADAR being field tested on a ship in 1939. Watson-Watt was another glory hound that falsely claimed to have invented RADAR. He did not actually get the idea. He took it from one of his subordinates.

Hi

Agilent App. Note 150:
Heterodyne means to mix - that is, to translate frequency - and super
refers to super-audio frequencies, or frequencies above the audio range.

Regrads