
164 Analog Circuits Cookbook
RF section
Figure 5.20 shows the RF/IF unit, which is powered via a ribbon cable
from the sweep circuit board. The gain of the TV tuner
IC%
can be varied
by means of i?4i, which thus substitutes for the input attenuator of a con-
ventional spectrum analyser. Compared with the latter, this spectrum mon-
itor has the advantage of a tuned front end, as against a wide open straight-
into-the-first-mixer architecture. The front end tuning helps to minimise
spurious responses - always a problem with any receiver, including spec-
trum analysers. The IF output of the tuner, covering approximately 34 -
40MHz, is applied via a ...