Circuit Descriptions and Serial Control Information
...... 4
Control bits
41
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
42
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
45
43
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
46
44
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Element
Squelch Threshold Voltage
3.500V d.c.
3.366
3.233
3.100
2.966
2.833
2.700
2.566
2.433
2.300
2.166
2.033
1.900
1.766
1.633
1.500
Squelch Source Selector
Notes
The fine squelch adjustment level from the Digital-
to-Analogue converter.
These threshold levels are used as a comparison
with the selected input noise voltage (bits 45 and
46).
Variation in V
DD
will produce variation in threshold
levels.
70.0% V
DD
67.3%
64.6%
62.0%
59.3%
56.6%
54.0%
51.3%
48.6%
46.0%
43.3%
40.6%
38.0%
35.3%
32.6%
30.0%
As well as selecting the input to the Noise
Comparator, these two bits produce additional
General Powersave (GPS) functions which control
those elements not having individual serial control.
0
0
A “Total Powersave” condition
Powersaved:
Input Gain Amp – Post Process
(2dB) Gain Amp – Mixer Amp – Noise BPF –
Noise Rectifier – Squelch Comparator
1
0
1
0
1
1
Noise Input selected to Comparator
R.S.S.I. input selected to Comparator
Powersave but LISTENING condition
R.S.S.I. input selected to Comparator
Powersaved:
Input Gain Amp – Post Process
(2dB) Gain Amp – Mixer Amp – Noise BPF –
Noise Rectifier
Rx Noise Path
Any high-frequency noise (18kHz/25kHz) present at the Rx Audio Input will also be available at
the Noise Output pin via the squelch filter and noise rectifier (when enabled) for use as a
squelch detection level. This means that the FX506 can be set to “LISTEN” with the majority of
circuit elements powersaved until an R.S.S.I. level is detected and produces a "Squelch Drive
output."
This path, when selected, can be used as a direct path, via the Output Drive Selector
(bits 18 and 19), to dynamically set and balance the VCO drive and reference output levels.
Test Signal Path
Reference ...... Figure 4
9
CMLMICRO [ CML MICROCIRCUITS ]
