0.5 mm enameled copper wire
close wound on 3.2 mm diameter former
RF
433 MHz = 24 turns
A. Helical antenna
Feed point 15% to 25% of total loop length
track width = 1mm
RF-GND
4 to 10 cm2 inside area
C2
C1
RF
C3
C4
B. Loop antenna
16.4cm
wire, rod, PCB-track or a combination
of these three
RF
433 MHz = 16.4 cm total from RF pin.
C. Whip antenna
Figure 5: integral antenna configurations
Packet data
In general, data to be sent via a radio link is formed into a serial "packet" of the form :-
Preamble - Control - Address - Data - CRC
Where: Preamble:
This is mandatory for the adaptive data slicer in the receiver in the NiM2 to
stabilise. The NiM2 will be stable after 10ms. Additional preamble time may be
desired for decoder bit synchronisation, firmware carrier detection or receiver
wake up.
Control:
The minimum requirement is a single bit or unique bit pattern to
indicate the start of message (frame sync.). Additionally, decoder
information is often placed here such as: packet count, byte count, flow
control bits (e.g. ACK, repeat count), repeater control, scrambler
information etc.
Address:
This information is used for identification purposes and would at least
contain a 16/24 bit source address, additionally - destination address,
site / system code , unit number and repeater address's may be placed
here.
Data:
CRC:
User data , generally limited to 256 bytes or less (very long packets
should be avoided to minimise repeat overheads on CRC failure and
channel hogging).
16/24 Bit CRC or Checksum of control-address-data fields used by the
decoder to verify the integrity of the packet.
The exact makeup of the packet depends upon the system requirements and may involve some complex
air-traffic density statistics to optimise through-put in large networked systems.
Radiometrix Ltd.,
NiM2 transceiver data sheet
Page 8
RADIOMETRIX [ RADIOMETRIX LTD ]
