Radiometrix Ltd.,

NiM2 transceiver data sheet

Page 8

A. Helical antenna

B. Loop antenna

RF

C1

C2

C4

C3

RF-GND

C. Whip antenna

16.4cm

RF

0.5 mm enameled copper wire

close wound on 3.2 mm diameter former

433 MHz = 24 turns

Feed point 15% to 25% of total loop length

track width = 1mm

4 to 10 cm inside area

wire, rod, PCB-track or a combination

of these three

433 MHz = 16.4 cm total from RF pin.

2

RF

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:

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).

CRC:

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.