JRC JSS-296 Service Manual page 217

To Whom It May Concern:
Notice for FEC-broadcasting reception using NBDP in MF/HF radio equipment
1. Objective Equipment
All kind of MF/HF radio models
2. Notice
The symptoms mentioned below may be occurred when receiving FEC broadcasting under noisy or
fading conditions.
- DTE (or Controller) displays and printer outputs " * (asterisk) ", unpredicted and/or
meaningless (garbled) characters.
- The equipment closes the link of channel and returns to stand-by mode by itself.
Please note that these symptoms are NOT malfunction of radio equipment because they are occurred by
the MF/HF frequency band characteristic and the occurrence mechanism could be explained as below.
The external noise and fading often change the receiving-signal-strength and may make it impossible to
receive signal at all even under linking in MF/HF frequency band. However NBDP would try to
continue to detect signals, and decode noises at that time. In such a case, the occurred symptoms and
the causes could be predicted as follows.
Both LCD and Printer output show * (asterisk).
Both LCD and Printer output show unpredicted
and meaningless (garbled) characters.
FEC reception is stopped and equipment returns
to stand-by mode.
Therefore the * (asterisk) marks and/or garbled characters, shown on the display and printer output,
and the process such as returning to stand-by mode on FEC reception are symptoms caused by the
unstable environment of radio wave propagation, and the equipment can be considered as normal.
3. Countermeasure against the symptom mentioned-above
Please adjust the RF GAIN volume to the maximum and/or select channel or FEC broadcast station so
that NBDP could obtain the receiving level as strong as possible.
____________________________
M. Takayama,
Manager
Network and Communication Group
Engineering Department
Marine Electronics Division
5-1-1, Shimorenjaku Mitaka-shi,
Tokyo, 181-8510 Japan
Tel: +82 422 45 9538
Symptoms
Mitaka Plant
Fax: +82 422 45 9957
By NBDP function to notify of receiving noises detected.
By decoding of noise misjudged as correct data.
Note) TELEX communication certainly makes use of error detection
standardized by ITU-R M625 & M476 so each character code
should be consisted of both 3bits for "1" and 4bits for "0". But
this error check might misjudge noises as correct data if it
were detected as the correct rate accidentally.
By NBDP specification prescribed by the above-mentioned
regulation so that FEC reception should be discontinued by
force if detected error frequently and judged continuous
reception to be hard any more.
Causes