The Transistor Superhet

Of all the many types of receivers that have been designed the super
net, invented by Arm- strong in 1918, is almost the only type in common
commercial use today. This applies as much to transistors as it does to
valves. There are several excellent reasons for this unique state of
affairs. First of all, the well designed superhet has better
sensitivity and selectivity than any other type, furthermore the
quality is also first class. Secondly, however many stages of
pre-demodulation amplification may be used, only two variably tuned
stages are necessary. The disadvantages are mainly difficulty of align-
ment and fairly high cost.

One of the disadvantages of the T.R.F. type of receiver is the
dependance of its gain upon frequency. The superhet attempts to
overcome this by changing the frequency of the incoming signal to a
certain fixed value and then amplify- ing this intermediate frequency
with fixed tuned circuits.”