MTX2 Datasheet, PDF (8/10 Pages) Radiometrix Ltd – UHF Narrow Band FM sub-miniature transmitter

Antenna requirements
Three types of integral antenna are recommended and approved for use with the module:
A) Whip
This is a wire, rod ,PCB track or combination connected directly to RF pin of the module.
Optimum total length is 16.4cm (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
B) Helical
Wire coil, connected directly to RF pin, 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.
C) Loop
A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and fed
from RF pin at a point 20% from the ground end. Loops have high immunity to proximity de-
tuning.
Feature
Ultimate performance
Easy of design set-up
Size
Immunity proximity effects
Range open ground to similar antenna
A
whip
***
***
*
*
500m
B
helical
**
**
***
**
200
C
loop
*
*
**
***
100
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.
A. Helical antenna
0.5 mm enameled copper wire
close wound on 3.2 mm diameter former
RF
433 MHz = 24 turns
C2
C3 C4
B. Loop antenna
16.4cm
C. Whip antenna
Figure 7: Antenna types
RF-GND
C1
Feed point 15% to 25% of total loop length
track width = 1mm
4 to 10 cm² inside area
RF
wire, rod, PCB-track or a combination
of these three
RF
433 MHz = 16.4 cm total from RF pin.
Radiometrix Ltd
MTX2 Data Sheet
page 8