13
iO1000 Detailed Service Manual - THEORY OF OPERATION
becomes negative and the LO phase is adjusted. This phase adjustment is per-
formed twice on the I channel with positive and negative values. See Figure 7 on
page 13.
Figure 7. Phase Training
Receiver Path Section
The iO1000 receiver is a double-conversion, superheterodyne receiver (see
Figure 8 on page 14). It operates in the commercial portion of the land-mobile
receiver band (851-866 MHz). The receiver takes an incoming RF signal, down-
converts it to a filtered109.65 MHz frequency (IF stage), and converts it to base
band. The signal is then digitized.
The receiver has automatic gain control (AGC) to maintain good linearity over a
wide range of incoming signals. The AGC circuitry also prevents clipping of high-
level signals.
I
LO
DOWNMIXER
0
°
and 90
°
Phase
Adjust
0
°
and 90
°
RF IN
UPMIXER
Switch
Comparator
RF OUT
Transmitter
Output
∑
∑
+
-
