NTR2 RADIOMETRIX [Radiometrix Ltd], NTR2 Datasheet - Page 7

• Manufacturer Part Number: NTR2
• Description: UHF Narrow Band FM Transceiver
• Manufacturer: RADIOMETRIX [Radiometrix Ltd]

Antennas
The choice and positioning of transmitter and receiver antennas is of the utmost importance and is the single
most significant factor in determining system range. The following notes are intended to assist the user in
choosing the most effective antenna type for any given application.
Integral antennas
These are relatively inefficient compared to the larger externally-mounted types and hence tend to be
effective only over limited ranges. They do however result in physically compact equipment and for this
reason are often preferred for portable applications. Particular care is required with this type of antenna to
achieve optimum results and the following should be taken into account:
1. Nearby conducting objects such as a PCB or battery can cause detuning or screening of the antenna
2. Microprocessors and microcontrollers tend to radiate significant amounts of radio frequency hash which
A simple test for interference is to monitor the receiver RSSI output voltage, which should be the same
regardless of whether the microcontroller or other logic circuitry is running or in reset.
The following types of integral antenna are in common use:
Quarter-wave whip. This consists simply of a piece of wire or rod connected to the module at one end. At
434MHz the total length should be 164mm from module pin to antenna tip including any interconnecting wire
or tracking. Because of the length of this antenna it is almost always external to the product casing.
Helical. This is a more compact but slightly less effective antenna formed from a coil of wire. It is very
efficient for its size, but because of its high Q it suffers badly from detuning caused by proximity to nearby
conductive objects and needs to be carefully trimmed for best performance in a given situation. The size
shown is about the maximum commonly used at 434MHz and appropriate scaling of length, diameter and
number of turns can make individual designs much smaller.
Loop. A loop of PCB track having an inside area as large as possible (minimum about 4cm
matched with 2 capacitors. Loops are relatively inefficient but have good immunity to proximity detuning, so
may be preferred in shorter range applications where high component packing density is necessary.
Integral antenna summary:
Radiometrix Ltd.,
Feature
Ultimate performance
Ease of design set-up
Size
Immunity to proximity effects
which severely reduces efficiency. Ideally the antenna should stick out from the top of the product and
be entirely in the clear, however this is often not desirable for practical/ergonomic reasons and a
compromise may need to be reached. If an internal antenna must be used try to keep it away from other
metal components and pay particular attention to the “hot” end (i.e. the far end) as this is generally the
most susceptible to detuning. The space around the antenna is as important as the antenna itself.
can cause desensitisation of the receiver if its antenna is in close proximity. The problem becomes
worse as logic speeds increase, because fast logic edges generate harmonics across the UHF range
which are then radiated effectively by the PCB tracking. In extreme cases system range may be reduced
by a factor of 5 or more. To minimise any adverse effects situate antenna and module as far as possible
from any such circuitry and keep PCB track lengths to the minimum possible. A ground plane can be
highly effective in cutting radiated interference and its use is strongly recommended.
whip
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NTR2 transceiver data sheet
helical
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loop
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2
), tuned and
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