Below you can find a few useful tips on MANCHESTER coding / decoding operation on EZradio PRO to clarify some common misconceptions.
The DR in the modem DOES NOT change with the MAN coding/decoding feature enabled. The DR in the air is always configured by the “Data rate” entry field on tab “RF parameters” in WDS. It follows than that if at the TX side you enable MAN coding on your whole packet, it will be twice as long.
If MAN coding is enabled on a standard preamble of 0x55 55 55 the result will be a NON STANDARD preamble of 0x66 66 66 66. If the standard nature of the preamble is required after MAN coding (which may have some benefit at the receive side) the Manchester Constant feature must be enabled at the Preamble setup on the “Packet” tab. This feature will simply replace the standard preamble pattern with either an all zero or an all one trail (dependent on the original preamble being 0x55 or 0xAA) so after MAN coding it will look like a standard preamble again.
MAN decoding on the preamble at the Rx side only takes effect if non-standard preamble detection is configured. This is the only case when the detection happens in the packet handler, at all other cases it is the either done in the modem (standard preamble) or skipped entirely (no preamble detection).
MAN coding / decoding can be separately applied to the preamble, sync word and data fields. The CRC (when enabled) is also MAN coded at the Tx side and is checked after decoding at the Rx side.
When transmitting a preamble in 4(G)FSK mode MAN coding is not recommended as it will alter the frequency symbols in a way that the preamble pattern is no longer transmitted as an alternating pattern between the two OUTERMOST symbols. This is a requirement for the receiver to be able to perform a robust preamble detection. When transmitting in 4(G)FSK mode the modulator is always in 4(G)FSK mode. The preamble is composed, however in such a way in the packet handler that it only uses the outer frequency symbols. I.e., the bit stream that is given to the modulator from the packet handler is „pre-coded”. Let’s assume a commonly used grey coded symbol mapping of: 00 01 11 10 -> -3df, -1df, +1df, +3df. In such a case the packet handler will compose a preamble sequence of 0010 0010 0010... This is the default case where you observe a preamble pattern in the air that alternates between the outer frequency symbols. Now, if you enable Manchester coding it will be done on this pre-coded bit sequence which in this particular example (with a Manchester scheme of 0->01 1->10) will result in an alternating pattern between -1df and +3df. If you select the Manchester constant feature it will simply override the pre-coding of the preamble to a constant 1 (or constant 0). The result in our example in such a case will be a constant transmission of +3df symbols.
For reference here is a list of other MAN coding / decoding related KBs: