Quartzlock E6-SS User Handbook Manual - page 9
Model
E6-SS
Operation Manual
E6-SS Manual A5 29 September 2015
Page 9
Various modulation modes are available, described in detail as follows:
AM.
AM is available on low range only. Depth is adjustable from 0 to 40% in
steps of 1%. AM modulation frequency is adjustable from 1Hz to 20kHz in
steps of 1Hz. AM is achieved by modulation of the low range amplitude
control DAC. The modulation frequency is generated by a software DDS
with a sampling frequency of 65,57377ks/s
FM (internal)
Internal FM is available with deviations up to 0.5% of the centre frequency,
adjustable in 1Hz steps. Modulation frequency is adjustable from 1Hz to
20kHz in 1Hz steps. Internal FM is achieved by direct modulation of the
synthesizer fractional divider. The modulation offsets are generated by a
software DDS with a sampling frequency of 65,57377ks/s. The offsets to the
fractional divider have 16 bit quantization.
As no baseband filter is used after the software DDS, aliased copies of the
modulation spectrum will be present at multiples of the sampling frequency.
These are typically- 50dB relative to the main response.
FM (external)
DC coupled external FM is available by supplying a suitable modulation
waveform to the external modulation input BNC socket on the rear panel.
The input range is ±1Volt for calibrated deviations, and ±1.25V clipping
level. The input impedance is 1kohm.
The input waveform is sampled at a 40ks/s rate using a 12bit ADC. The
result is then scaled by the selected deviation, and is used to directly
modulate the synthesizer fractional divider. As no baseband filter is used, the
modulation spectrum will repeat at multiples of the sampling frequency,
typically at a level of –50dB relative to the main response.
FSK (external)
Frequency shift keying is available by applying a logic input to the external
modulation input on the rear panel. The logic levels are TTL or 3.3V
CMOS. A logic 0 produces a negative frequency shift, and a logic 1 a
positive shift. The total frequency shift is that programmed for internal FM
deviation. i.e., a programmed deviation of 10kHz produces a frequency shift
of ±5kHz. The maximum baud rate is about 35kbaud. If the maximum rate is
exceeded, data bits will be skipped.