
Radio-frequenc]^ circuits 203
as to implement an L pad,'* which is matched in one
direction (see Figure 8.1 la), or a Τ or π pad, which
is matched from both sides. In principle, an
attenuator matched both ways can be implemen-
ted with only two diodes if the bridged Τ circuit is
used (Figure 8.11b).
It is only when receiving signals where the
modulation results in variations of signal ampli-
tude,
such as AM and SSB, that AGC is required.
With FM, PM and certain other signal types, no
information is contained in the signal amplitude -
other than an indication as to how strong the signal
is.
Any variations in amplitude are therefore
entirely adventitiou ...