QM Receiver Module
Application Information
Antenna Design
The design and positioning of the antenna is as
crucial as the module performance itself in
achieving a good wireless system range. The
following will assist the designer in maximising
system performance.
The antenna should be kept as far away from
sources of electrical interference as physically
possible. If necessary, additional power line
decoupling capacitors should be placed close to
the module.
The antenna ‘hot end’ should be kept clear of any
objects, especially any metal as this can severely
restrict the efficiency of the antenna to receive
power. Any earth planes restricting the radiation
path to the antenna will also have the same effect.
Best range is achieved with either a straight piece
of wire, rod or PCB track @ ¼ wavelength
(15.5cm @ 433.92MHz). Further range may be
achieved if the ¼ wave antenna is placed
perpendicular in the middle of a solid earth plane
measuring at least 16cm radius. In this case, the
antenna should be connected to the module via
some 50 ohm characteristic impedance coax
QMR1 / QMR2
Receiver Data Output Buffer
The QMR1 receiver has a push-pull data output
drive limited to 20uA. If drive problems are
experienced, and sometimes they exhibit
themselves in a poor system range, the following
simple buffer stage should be incorporated
between the module data output and the
subsequent stage. This buffer is already present
on the QMR2 receiver.
+5V
Data From
Receiver
1K5
U1
Data Out
+5V
U1 = SOT23 Package
part number BU4581 (ROHM)
Figure 6: Receiver Data Output Buffer
Helical Antenna
RF
34mm @ 433MHz
17 turns equally spaced
∅
= 5mm (inside)
Whip Antenna
RF
15.5cm @ 433MHz
Figure 5: Antenna Configurations To Be Used
With The Modules
Ds302_3
AUG 01
©
2001 REG No 277 4001 England
Page 5
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