the double tone is -3dB, and the reference frequency to which the distortion is referred is
0dB.
Intermodulation distortion
4.16 Tone Burst/Tones Segment (!) FSK decoders ASK decoders Testing FSK decoders
The tone burst segment (‘!’) is a very powerful facility for generating tones and tone
bursts. It can also be used to design new segments similar to standard segments but using
different frequencies or levels. Because this facility is so flexible it has been used for
many different applications, including: meter testing, generating FSK and ASK test
signals for testing decoders, generating morse code for identifying a transmitter source
and even playing tunes.
Multiple tone bursts Generating tones Intermittent tones Tone bursts
The ! character is followed by frequency duration and (optional) level parameters:
!f,d Generate f Hz for d ms (at 0dB), then silence.
!f,d,l Generate f Hz for d ms at l dB, then silence.
It is also possible to specify the frequency, level and duration of up to 32 tones with a
single ! segment:
!f
1
,d
1
,l
1
,f
2
,d
2
... Generate f
1
Hz for d
1
ms at l
1
dB, then f
2
Hz for d
2
ms at l
2
etc
The frequency f will be rounded to the nearest that can be generated. 0 is allowed and
corresponds to the DC0 state (silence) which is useful before or after tone bursts. The
output is not muted in this condition, because relay switching may produce undesirable
transients.
The duration d in ms should be in the range 0ms to 1600000.0ms (ie 27 minutes) and may
be specified to 1 decimal place (ie 100µs resolution). Timing is very accurate (±50µs or
±0.01%) when the level for a tone is not specified. If the level is specified the timing
accuracy will be reduced slightly. A duration of 0 for the last tone in the list will cause
the last tone to be held after the segment has terminated instead of silencing. This is only
relevant in single segment mode (segment T behaves in this way) but can be useful for
programming sets of presets on the number keys (see example 3 below).
The level l in dB (relative to Test Level) should be in the range -101.99 to +26.00 and
may be specified to 2 decimal places. Transitions between tones where the absolute level
of one is above -38dBu and the other is below -38dBu may result in a small click (lasting
2-3ms) as a relay is switched for levels below -38dBu.
! tone segment Generating tones Tone bursts
The default value for any parameter is its previous value in the same segment if specified
(default value for first occurrence is 0 for f, d and l). Note that this can considerably
shorten definitions. There is no limit to the number of ‘!’ segments in a sequence, but
there is a limit of 32 tones per ‘!’ segment. More than this will generate a ‘
TOO MANY
TONES
’ error. In the unlikely event that you need to generate more than 32 tones, try
78
4. User Defined Sequences
To Next Page
Loading...