410mm @ 173MHz
R
F
wire, rod, PCB track
or a combination of these
Whip antenna
length(mm) = 71250 / freq(MHz)
35-40 turns wire spring
length 120mm, dia 10mm
R
F
trim wire length or expand coil for
best results
Helical antenna
track width = 1mm
min. area 500mm2
RF
Cmatch
capacitors may be variable or fixed
(values depend on loop dimensions)
C
tune
RF GND
Loop antenna
Fig.10: integral antenna configurations
Integral antenna summary:
whip
***
***
*
helical
loop
*
*
**
***
Ultimate performance
Ease of design set-up
Size
**
**
***
*
Immunity to proximity effects
**
Tamper-proof integral antenna
Where the RX1 is used in alarm applications it may sometimes be necessary to provide a warning if any
attempt is made to remove or disable its antenna. A typical solution to this problem is as follows:
1/4 wave
hairpin loop
antenna
RX1
2
3
4
8
7 9
1
5
6
R2
1n
to comparator circuit, etc.
R1
Fig.11: Tamper-proof antenna arrangement
In normal operation the output will have a resistance to ground of R1+R2. If the antenna is shorted to
ground it will show R2 only, and if the antenna is cut it will be open-circuit.
R1 and R2 may be any value over 1kΩ. All track lengths should be kept to a minimum and the output
may need to be decoupled in some cases to avoid noise being injected into the antenna from the
following circuitry.
Radiometrix Ltd., TX1 & RX1 Data Sheet
page 11
RADIOMETRIX [ RADIOMETRIX LTD ]
