Adeunis RF ARF26 User Manual - Page 7

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PROTOCOL

On account of the ARF26 system transmission principle and of the modulation in phase lock

loop, the modulating signals must have a frequency comprised between 1 kHz and 25kHz.

Lower and higher frequencies cannot be transmitted, as they are filtered. This means, among

other things, that the link cannot transmit constant states with a duration of more than 500 µs.

• Level - Bit Encoding

Most conventional hardwired serial links transmit bytes in asynchronous manner using an

NRZ type encoding (1 logic bit = 1 electrical state). This results in the spectrum occupation of

the signals thus generated being about one decade. Furthermore, sampling of the bytes thus

received supposes perfect synchronisation of decoding on the start bit.

In the case of radio transmission, it is preferable to limit the spectrum of the signals to be

transmitted as far as possible, in particular towards low frequencies, even if this means

increasing the main frequency. Moreover, it is advantageous to reset the synchro on each

transmitted bit; receivers are in fact the cause of large duty cycle errors on the electrical states.

Bit encodings should therefore be preferred, for example those proposed below:

Manchester or two-phase:

Differential PWM:

• Level - Frame Encoding

Once the bits have been encoded, it is then imperative that they be transmitted according to a

frame structure; the radio link is very sensitive to binary flow breaks which can only be

minimised by "serialising" the bytes.

A conventional frame structure is shown below:

05-11-V3-psn