Mixer (D3258); Uhf Range 1 (380-470 Mhz) Band; Figure 3-14. Receiver Front-End And Back-End (Uhf Range 1) - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

Theory of Operation: Receiver Front-End

3.4.1.5 Mixer (D3258)

The received signal is down-converted by a double-balanced mixer to an Intermediate Frequency
(IF) of 109.65 MHz. The mixer is designed to provide low conversion loss and high intermodulation
performance. The injection buffer provides a 20 dBm LO signal to the mixer. High-side injection is
used.
3.4.2 UHF Range 1 (380–470 MHz) Band
The receiver circuits primary duties are to detect, filter, amplify, and demodulate RF signals in the
presence of strong interfering noise and unintended signals. The receiver (see
broken down into the following blocks:
• Front-end, which includes:
- High pass fIlter and first low-noise amplifier (LNA)
- Preselector filter
- Switchable 15 dB attenuator
- Second LNA
- Image Filter
- First mixer
• Back-end, which includes:
- Intermediate Frequency (IF)
- ABACUS III IC
RF Input
Pre-Amp
Ant. SW.
Switch
Harm. FLT
High Pass
Filter

Figure 3-14. Receiver Front-End and Back-End (UHF Range 1)

6881096C74-B
380-470MHz
Pre-Amp
Pre-Amp
Switch Preselector 15 dB
Switch
Att.
A
LNA
Low Pass
Pre-Amp
Mixer
Filter
Switch
24dBm
LNA
1st LO
2nd LO
LO Synth.
ABACUS III IC
Backend A/D Converter
3-15
Figure 3-14) is
109.65MHz
Crystal IF Amp Crystal
10 dB
Att.
A
Dec.
ADC SSI
Filter
CLK
18MHz
Synth.
CLK
May 25, 2005