|
| |
Back
SUMMARIZE | Up
Fire Controlman Volume 06-Digital Communications | Next
PHASE ERR M |
Figure 3-11.—The LMS-11 Net Display in PU History Mode.
SNR.— The signal-to-noise ratio, measured in dB.
The SNR is calculated as the average power in the
data tones divided by the average power in the noise
tones. The LMS-11 can measure a SNR of near 34
dB. A number preface by the greater than symbol “>”
indicates that the average power in the noise tones
was below the measurable threshold. In this case, the
number represents the data tone signal strength only.
An SNR value of 30 or higher is considered excellent.
An SNR value of less than 10 is unusable.
FRAME CNT.— A count of all data frames
received over the specified number of cycles. Data
frames include the phase reference frame and control
code frames in each message.
A value that is
followed by a “?” and color-coded yellow is displayed
if the frame count of a picket station average is less
than or equal to six frames. The two start code
frames, the phase reference frame, the crypto frame,
and the two stop code frames account for the six
frames. Therefore, if a picket unit transmits six or
less frames, no actual message data is being received.
This may indicate a problem with either the computer
or the DTS of the unit. A yellow color-coded value
followed by the “?” is added for an NCS when the
number of frames is equal to or less than eight. The
two additional frames account for the next station
address at the end of an NCS report.
%THRU.— This number is the percentage of
message data that is received error-free.
The
percentage is found by comparing the number of
error-free message data frames with the total number
of message data frames received.
CF.— This is a percentage of control code failures.
A PU with strong signals that never misses a call will
have a 0 % code failure. A PU that never answers,
such as a dummy PU, will have a 100 % code failure.
Values between 1 and 100 could be due to noise or
weak equipment or an equipment malfunction.
BER.— This is the bit error rate measured as the
number of bit errors per 1,000. Bit errors increase as
the signal-to-noise ratio decreases. A bit error rate
that exceeds a theoretical value for a given SNR is
indicated by displaying both the BER and SNR in
yellow.
3-14
|
