Lambda SR1, Operation Manual, Page: 42 / 317

SR1 Operation Manual 42
© 2014 Stanford Research Systems
Unit Description
Vrms and Vp always have this fixed relationship. Irrespective of waveform, 1 Vrms = 1.414
Vp.
Vpp Similar to rms, Vpp (Volts peak-to-peak) has the same relation to Vp that it does for a
sinewave. Thus, 1Vpp = .5 Vp.
dBVrms Decibels relative to 1 Vrms. A signal with an amplitude of -20 dBVrms has a peak
amplitude of 100 mVrms or 141.4 mVp.
dBu Decibels relative to 0.7746 Vrms. Note that even though historically the value of 0.7746
Vrms was chosen because it represents the voltage required to dissipate 1 mW in a 600
load, in SR1 dBu specifies an open-circuit voltage without regard to the actual load
connected to the output.
dBr Decibels relative to the dBr Reference specified in the References Box .
dBm Decibels relative to 1 mW into a load specified by the dBm Reference in the References
Box . Specifying the waveform amplitude in dBm asks SR1 to set the amplitude necessary
to deliver a certain amount of power to a specified load taking into account the output
impedance of the generator. If the amplitude is measured across the open-circuited output
terminals with a high-impedance meter, you may get a different result.
W Watts into a load specified by the dBm Reference in the References Box . Specifying the
waveform amplitude in dBm asks SR1 to set the amplitude necessary to deliver a certain
amount of power to a specified load taking into account the output impedance of the
generator. If the amplitude is measured across the open-circuited output terminals with a
high-impedance meter, you may get a different result.
The value of "0" has no exact representation in dB units. When a generator amplitude of
0 is shown in a control displaying dB units the value "-1000 dB" is shown (which may
display as "-1.0 kdB". This is not meant to imply an actual value of negative 1000 dB
but merely to provide a convenient way to represent 0 in dB units.
Analog Generator Frequency Units
The following table describes the units used by SR1 in setting the frequency of digital generator
waveforms. All frequency units except Hz make use of the Frequency Reference which is set in the
References Box on the Analog Generator Panel.
Unit Description
Hz The fundamental unit of frequency. 1 Hz = 1 cycle-per-second.
F/R Ratio relative to the Frequency Reference. A value of 3 F/R with reference of 2 kHz gives a
waveform frequency of 6 kHz.
dHz Difference relative to the Frequency Reference. A value of 500 dHz with a reference of 2
kHz gives a waveform frequency of 2.5 kHz.
%Fref Percent of the Frequency Reference. A frequency value of 50 %Fref with a reference value
of 10 kHz gives a waveform frequency of 5 kHz.
cents A "cent" is a logarithmic unit which represents 1/100 of a semitone of the musical scale.
12 semitones make up an octave. Thus a cent is 1/1200 of an octave.
octaves An octave is a factor of 2 in frequency. Thus, a frequency value of 3 octaves with a
reference of 1 kHz gives a waveform frequency of 8 kHz.