Technical data

Installation & Operation Manual GM-TTT
Page 61
5.2 DCF IN Option: Installation of a DCF77 Receiver
If a DCF77 receiver is installed in the GM-TTT, only the antenna remains to be connected at
the OPTION 1 connector of the rear panel (BNC 50).
The DCF77 receiver is equipped with an autonomous, battery-buffered clock which continues
to count the time during power failure or in free-run mode - when no signal is received - with
an accuracy of about 10
-5
. This clock is set as soon as synchronisation is achieved, and
generally it is sufficient to perform synchronisation again once or twice a day. The receiver
transmits time, date and status data to the processor of the GM-TTT via an internal serial
interface. Normally, the clock of the receiver is set to CET/ CEST.
Antenna installation:
According to a basic principle, an antenna has to be installed upon the roof! Many
problems are avoided when this guideline is followed.
The antenna should never be placed in close neighbourhood of computers or video
monitors.
The mod. and free LED’s serve to ensure the optimum alignment of the antenna. The mod.
LED is directly controlled by the receiver and imitates the radio telegram, whereas the free
LED shows, if the serial data of the receiver indicate the “lock“ status. The antenna should
be set up in an upright position and slowly rotated, until the mod. LED is periodically
flashing every second - without any flickering! After some minutes, the free LED must go
off. If it does not, the antenna should be installed at a different location.
Remark: In the radio telegram, the 59
th
second is characterised by the omission of the
seconds pulse, i.e. the mod. LED does also not flash.
The GM-TTT displays further status data permitting to survey the receiver, please refer to
chapter “3.8.3 1... 6: Status Data of the Reference Time“.
It is recommended to use the following parameters for operation with this reference time:
In the REFER - MODE 1 menu:
Digit 8
Digit 7 Digit 6
Digit 5 Digit 4 Digit 3 Digit 2 Digit 1
, i.e. time and date of the
DCF77 receiver are adopted after power-on and periodically once a day. The reference time
is handled like a CET/CEST, and the time of the internal clock of the GM-TTT should generally
also correspond to this time zone (parameters in the ZONE menu: OFFS1 = 00, OFFS2 =
01).