Meinberg DCF77, Operating Instructions Manual

Page: 11 / 18

11
Aligning the antenna
Generally, the exact alignment of the antenna is important. It has to be placed in
longitudinal direction to the transmitter (Frankfurt), see arrow printed on the label of
the antenna.
A distance of several meters to TV- or computer monitors, to computers or
microprocessor boards should be kept. These devices can produce interference fields
that lead to a poor or no DCF77 receiption. If it is not possible to mount the antenna
with a sufficient distance to the computer monitor, it’s line frequency should not be
close to the RF-frequency of DCF77 (77.5 kHz).
The antenna should be installed with a minimum distance of 30cm to all metal
objects. Otherwise the ferrite antenna will be detuned and the received power decrea-
ses.
Alignment of the antenna can be done by watching the modulation and field
strength LEDs. Like described in chapter „General information about DCF77“, undis-
turbed pulses per second (except 59. second) without any interfering pulses are
required for corrcect decoding of the DCF77 time telegram. Therefore, a modulation
LED blinking exactly once per second is a criterion for good receiption of the DCF-
signal.
Because PEX511 uses a quadrature demodulator as receive circuit, it is possible to
evaluate the field strength of the DCF77 signal only. Interfering signals within the
bandwith of the receiver have no affect on the brightness of the field strength LED
therefore.
If the radio clock is installed in the computer, it may be difficult to use the status
LEDs for alignment of the antenna. Therefore modulation and field strength can be
observed by using the monitor program „MbgMon“ (part of the shipped driver) also.
Modulation is displayed as a LED, the DCF77 field strength as a bar graph. Optional-
ly, the modulation signal can be made audible via the speaker of the computer.