A) Helical
Wire coil, connected directly to pin 2, open circuit at other end. This antenna is very
efficient given it's small size (20mm x 4mm dia.). The helical is a high Q antenna, trim
the wire length or expand the coil for optimum results. The helical de-tunes badly with
proximity to other conductive objects.
B) Loop
C) Whip
A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and
fed from pin 2 at a point 20% from the ground end. Loops have high immunity to
proximity de-tuning.
This is a wire, rod, PCB track or combination connected directly to pin 2 of the module.
Optimum total length is 15.5cm (1/4 wave @ 433MHz). Keep the open circuit (hot) end
well away from metal components to prevent serious de-tuning. Whips are ground plane
sensitive and will benefit from internal 1/4 wave earthed radial(s) if the product is small
and plastic cased
The antenna choice and position directly controls the system range. 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
Duty Cycle requirements
The duty cycle is defined as the ratio, expressed as a percentage, of the maximum transmitter “on” time
on one or more carrier frequencies, relative to a one hour period. Where an acknowledgement message
is required, the additional transmitter “on” time shall be included.
There is a 10% duty cycle restriction on 433.050-434.790 MHz band in most of the EU member states.
The TX2-433 is a RF module intended to be incorporated into a wide variety of applications and finished
products, Radiometrix has no control over the end use of the TX2-433.The harmonised band 433.050 to
434.790 MHz as detailed in Annex 1 Band E of CEPT/ERC Recommendation 70-03 (which can be
downloaded at http://www.ero.dk/scripts/docmanag98/dm.dll/QueryDoc?Cat=Recommendation)
has list of countries where Duty Cycle restriction apply.
Module users should, therefore, ensure that they comply with the stated Duty Cycle requirements of
the version of CEPT/ERC Recommendation 70-03 in place at the time of incorporation of the TX2-433
into their product. It should be noted that the stated Duty Cycle must not be exceeded otherwise any
approval granted for the TX2-433 will be invalidated.
Radiometrix Ltd., TX2 & RX2 Data Sheet
page 8
