User's Manual

TX RX Systems Inc. Manual 7-9485-1.7 09/12/11 Page 2
tions for the 613-8 family of channelized signal
boosters are listed in Table 2.
Down / Up Conversion
A channelized signal booster has much in common
with a superheterodyne (superhet) receiver. The
incoming signal is converted to a lower frequency
so that single channel selectivity can be obtained.
It is then filtered. Unlike the superhet receiver how-
ever, the signal is not demodulated. Instead, it is
up-converted back to its original frequency where it
is further amplified to reach a useful power level.
Figure 1 shows a simplified block diagram that
illustrates the down/up conversion principle. An
incoming signal at (Freq IN) is amplified and
applied to the first mixer along with a signal from a
local oscillator (Freq LO). A third signal at an inter-
mediate frequency (Freq IF) is produced as a result
of the mixing. The intermediate frequency is given
by the following relationship:
(1) Freq IF = Freq IN - Freq LO
The IF signal from the mixer then passes through
digital filtering with single channel bandwidth
before being amplified and passed on to the sec-
ond mixer. The second mixer also receives the
same local oscillator signal (Freq LO). The result is
a mixing product frequency at the output of mixer
2. The output frequency (Freq OUT) is given by the
following relationship:
(2) Freq OUT = Freq IF + Freq LO
Substituting equation (1) for the “Freq IFterm in
equation (2) allows the “Freq LO” terms to be can-
celed yielding:
(3) Freq Out = Freq IN