Application Notes
+5V
13
+5V
22K
DC BIAS
DC BIAS
+
-
JAM
10
JAM TC
12
+
DET
11
RSSI
0 - 3.3 v
22K
+5V
-
BUFFER
SAW 1st Local
Oscilltaor
433.92 MHz
2nd Local
Oscillator
16 MHz
9
6K8
MAX
+
Ve peak
detector
7
+5V
RF IN
STRENGTH
AF
2nd MIXER
IF AMPLIFIER
DEMODULATER
418 MHz
BPF
PRE-AMP
22K
+
1
1st MIXER
DATA
1M
6
MIN
-
Ve peak
detector
-
5
AF
BUFFER
DE -EMPHASIS
4
330R
+5V
+5V
0.9 V
22K
22K
+
TAMPER
RFC
-
0 V
3
RF GROUND
2
Internal block. Fig 4
The simplest applications of the module requires only 3 connections, +5V supply, ground and the data
output. A simple quarter wave antenna (17cm of wire or track on pin 1) will give good results. A 10µF
supply decoupling capacitor is recommended directly on pin 13.
ANTENNA
The positioning of the antenna is of the utmost importance and is the main determining factor of system
range, the following notes should assist in obtaining optimum performance:-
Keep it clear of other metal in the system, particularly the ‘hot’ end. The best position by far, is sticking
out the top of the product. This is often not desirable for practical/ergonomic reasons thus a
compromise may need to be reached. If an internal antenna must be used try to keep it away from
other metal components, particularly large ones like transformers, batteries and PCB tracks/earth
plane. The space around the antenna is as important as the antenna itself.
Keep it away from interference sources, bad interference can easily reduce system range by a factor of 5.
High speed logic is one of the worst in this respect, fast logic edges have harmonics which extend into
the UHF band and the PCB tracks radiate these harmonics most efficiently.
Single chip microprocessors and ground planed logic boards reduce this problem significantly. A simple
test for interference is to monitor the RSSI output of the receiver, there should be no change in the
reading when the logic circuits are run or held reset. Interference can also be easily identified by
listening to the AF output of the receiver, smooth white noise should be heard.
Radiometrix Ltd, RXM-UHF Data Sheet
page 6
RADIOMETRIX [ RADIOMETRIX LTD ]
