WH1080 protocol V2 – FSK

The Fine Offset weather station switched over to a new RF transmission protocol somewhere in 2012. While the old protocol was a On-Off-Keying (OOK) protocol, the V2 protocol used Frequency-Shift-Keying (FSK). This is natural transmision mode of the RFM02 transmitters and their RFM01 receivers. The RFM12B modules can also receive the same FSK signals. Most of the reverse engineering happened on the Raspberry Pi forum: WH1080 V2 protocol decoded

This post details on the exact transmission protocol.


Package definition:
[
preample 3 bytes 0xAA    synchron word    payload 10 bytes  postample 11bits zero
0xAA    0xAA    0xAA     0x2D    0xD4     nnnnn---nnnnnnnnn 0x00     0x0
101010101010101010101010 0010110111010100 101.............. 00000000 000
]
repeated six times (identical packages) per transmission every 48 seconds
There is no or hardly any spacing between the packages.
Spacing: to be confirmed.

When using the RFM01 or RFM12B, the preample and synchron word will not be in the received data. The preamble is intended to have the frequency synthesiser locked, while the synchron word serves as detection of the proper message.
Open issue: How can an end-of-transmission be detected? Would VDI turn into zero?
The payload contains to types of messages for FO WH1080, and relatives:

Payload definition:
Weather sensor reading Message Format:
AAAABBBBBBBBCCCCCCCCCCCCDDDDDDDDEEEEEEEEFFFFFFFFGGGGHHHHHHHHHHHHIIIIJJJJKKKKKKKK
0xA4    0xF0    0x27    0x47    0x00    0x00    0x03    0xC6    0x0C    0xFE
10100100111100000010011101000111000000000000000000000011110001100000110011111110


with:
AAAA = 1010    Message type: 0xA: sensor readings
BBBBBBBB       Station ID / rolling code: Changes with battery insertion.
CCCCCCCCCCCC   Temperature*10 in celsius. Binary format MSB is sign
DDDDDDDD       Humidity in %. Binary format 0-100. MSB (bit 7) unused.
EEEEEEEE       Windspeed
FFFFFFFF       Wind gust
GGGG           Unknown
HHHHHHHHHHHH   Rainfall cumulative. Binary format, max = 0x3FF,
IIII           Status bits: MSB b3=low batt indicator.
JJJJ           Wind direction
KKKKKKKK       CRC8 - reverse Dallas One-wire CRC

DCF Time Message Format:
AAAABBBBBBBBCCCCDDEEEEEEFFFFFFFFGGGGGGGGHHHHHHHHIIIJJJJJKKKKKKKKLMMMMMMMNNNNNNNN
Hours Minutes Seconds Year       MonthDay      ?      Checksum
0xB4    0xFA    0x59    0x06    0x42    0x13    0x43    0x02    0x45    0x74

with:
AAAA = 1011    Message type: 0xB: DCF77 time stamp
BBBBBBBB       Station ID / rolling code: Changes with battery insertion.
CCCC           Unknown
DD             Unknown
EEEEEE         Hours, BCD
FFFFFFFF       Minutes, BCD
GGGGGGGG       Seconds, BCD
HHHHHHHH       Year, last two digits, BCD
III            Unknown
JJJJJ          Month number, BCD
KKKKKKKK       Day in month, BCD
L              Unknown status bit
MMMMMMM        Unknown
NNNNNNNN       CRC8 - reverse Dallas One-wire CRC

The DCF code is transmitted five times with 48 second intervals between 3-6 minutes past a new hour. The sensor data transmission stops in the 59th minute. Then there are no transmissions for three minutes, apparently to be noise free to acquire the DCF77 signal. On similar OOK weather stations the DCF77 signal is only transmitted every two hours.

The package format was deduced using a long transmision buffer on a JeeNode with some modificaitons in the RF12 driver.
The payload definitions have been described at those pages:
WH1080 V1 OOK protocol
WH1080 V2 FSK protocol
WH1080 V1 OOK and DCF77 message format

This applies at least to the following (later) models:
Fine Offset WH1080
Alecto WS4000
National Geographic 265, at 916MHz