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This is a general list of terms and relationships commonly used in specifying DLVAs (Detector Log Video Amplifiers), ERDLVAs (Extended Range Detector Log Video Amplifiers), RF Log Amplifiers and Log IF Amplifiers. Graphs are included.

RF Bandwidth or Frequency Range: This defines the frequency range over which the specified performance and frequency flatness is achieved. Generally, the bandwidth can exceed the normal frequency range. If a particular band-shape is required, then the amount of rejection at the low and/ or high end of the frequency range should be specified. This is particularly important in the case of Log IF Amplifiers. Filtering can be integrated if necessary.

Tangential Signal Sensitivity (T. S. S.): This is the input RF power level (expressed in dBm) at which the device output exhibits a minimum Signal-to-Noise Ratio (SNR) of 8. 0 dB at the specified video bandwidth.

Usable or Operational Sensitivity: The usable or operational sensitivity is generally equivalent to a 14 dB output Signal-to-Noise Ratio (SNR). In general terms, this is approximately 5 dB stronger than the equivalent Tangential Signal Sensitivity (T. S. S.).

Threshold Sensitivity: Same as usable sensitivity.

Dynamic Range: Defined in dBs from T. S. S. to end of logging range. Very popular term that is generally confused with logging range.

Logging Dynamic Range or Logging Range: Defined in decibels (dBs) from usable sensitivity to end of logging range. Essentially indicates the range over which the signal information is processed and exhibits a straight line relationship with defined linearity between RF input power expressed in dBm and linear video output voltage usually expressed in millivolts (mV). See Figure 1.

Log Linearity: Describes the deviation of the actual output voltage from a straight line behavior. It is expressed in dBs. Log linearity is usually defined as either deviation from:

• A straight line whose slope is computed by the least squares method (best fit).
• A straight line whose slope is fixed (i.e., X mV/dB). This definition takes on added importance in D.F. systems or any time accurate relative power between two signals needs to be measured.

Log Slope: This is defined as the slope of the best fit straight line or slope of a defined fixed slope straight line which passes through the actual output voltage data over the whole logging dynamic range. It is expressed in mV/dB ± % mV/dB.

Incremental Log Slope: This is defined as slope of the best fit straight line or slope of a defined fixed slope straight line which passes through the actual output voltage data over a limited logging dynamic range, say every 1.0 dB or 2.0 dB.

Frequency Flatness: This is defined as the output voltage variation at a constant temperature and constant RF input power as the RF frequency is varied. It is expressed in ± dBs. See Figure 3.

Temperature Variation: This is defined as the output voltage variation referred to the input power (in dBs) at a given power level and given frequency, as the temperature is varied.

D.C. Output Offset: This is defined as the output D.C. voltage with no RF signal applied and input RF port terminated into a 50 Ohm termination.

D.C. Output Offset Variation: This is defined as the output offset voltage variation with no RF signal applied and as the temperature is varied over its operating range.

Absolute Accuracy: This is a measure of total power uncertainty around a fixed mathematical straight line (defined as a reference line) as the RF frequency, RF power and temperature are varied. The absolute accuracy includes the effects of log linearity, frequency, temperature variation and output D.C. offset variation. It is measured in ±dBs See Figure 4.

Propagation Delay: This is commonly defined as the propagation delay from 50% RF input to 50% video output. However, a more appropriate way of defining the delay time is from 50% RF input to 10% video output as the compression process changes the rise time as a function of power level. Sometimes called delay time. See Figure 5.

Rise Time (t_r): This is defined as the time response between 10% to 90% of the video output. See Figure 6.

Settling Time (t_s): This is defined as the time from 10% video output to a time when the video output has settled to ± X dB (commonly ±0.5 dB) of its final steady state value. It is generally 1.5 x rise time t_r.

Total Response Time: This is defined as time from 50% RF to when the video output has settled within ± X dB (commonly ±0.5 dB) of its final steady state value. It is usually equal to propagation delay plus settling time.

Dwell Time (t_d): This is defined as the minimum time for the output pulse to be Flat within ±X dB for the test condition of minimum required pulse width. It is generally equal to pulse width less settling time (t_s). Known also as Flat Top.

Fall Time (t_f): This is defined as the time required for the trailing edge of the pulse to fall from 90% value to 10% value for a given RF power level. Generally, the RF level is the highest power level of the logging range.

Partial Recovery Time: This parameter is critical when two pulse amplitudes need to be measured which are closely time spaced. This is defined as the time required for the output training edge to fall from 1.0 dB below peak to X dB below peak. Commonly, partial recovery is measured for a 16 dB or 20 dB drop in the output training edge voltage.

Recovery Time (t_rec): This is defined as the time difference between a threshold sensitivity minimum specified pulse width and a maximum logging range level pulse at the maximum specified pulse width so that the threshold sensitivity pulse can be measured within ±X dB (usually ±1.0 dB) of its value if the high level, wide pulse width would not be present. Generally, recovery time is defined from the 90% point of the falling video pulse to a point of ±1.0 dB of the base line. The DLVA is now recovered and able to accept a new RF pulse. Recovery time is sometimes known as Shadow Time because any new pulse occurring during recovery time would be shadowed.

Trailing Edge Re-Entrance: This specification describes and limits the trailing edge under shoot, its positive excursion and ringing behavior during the recovery time. Usually, the positive excursion or ringing of the trailing edge is specified to be below a level equivalent to threshold sensitivity.

Pulse-on-Pulse or Pulse-on-C.W.: This describes a requirement in the unit whereas pulse amplitude of the signal riding on a C.W. or RF noise level can be accurately measured. Usually, the pulse level can be either weaker or stronger than a specified C.W. or noise level and in both cases needs to be measured accurately.

C.W. Immunity Dynamic Range: This defines the C.W. range above threshold sensitivity level so that a pulse level at threshold sensitivity level can be measured within a specified error value, while rejecting the C.W. level.

C.W. Rejection Time: This describes the time required by the device design to cancel the maximum specified C.W. level so that the pulse level at the threshold sensitivity value can be measured within specified error value. Rejection time can be different when C.W. turns on and when C.W. turns off, and needs to be specified for a given device design.

Trailing Edge Discontinuity Range: This defines a range in dBs from a given peak value so that trailing edge does not show any perturbation, ringing, change of sign, etc. Usually, this range is from 1.0 dB below peak to 16 dB below peak level, and is critical when pulse width is required to be measured. Usually, discontinuity or perturbation is defined as abnormality wider than 5.0 nanoseconds in width.

Minimum Detectable Signal (M.D.S.):

M.D.S. = -114 + NF + 10 Log 2B_rB_v - B_v2
where NF is Noise Figure in dBs
Br is RF Bandwidth in MHz
Bv is Video Band in MHz
Also known as maximum sensitivity, or S_max. Expressed in dBm.

Tangential Signal Sensitivity (T.S.S.): Generally, a signal 4 dB stronger than Minimum Detectable Signal.
T.S.S. = M.D.S. + 4 dB
Also defined as a pulse where Signal-to-Noise Ratio (SNR) at RF is equal to 4 dB or Video Output SNR is equal to 8 dB.

Usable Sensitivity (S_u): Usable sensitivity (S_u) or point where initiation of logging begins and RF Input Power and Video Output Voltage are (or approximate) a straight line. Generally, a signal 5 dB stronger than Tangential Sensitivity Signal:
S_u = T.S.S. + 5 dB

Relationship Between Video Bandwidth (B_v) and Rise Time (t_r):
B_v = 0.35 where: B_v is in Hz
                                        t_r     t_r is in seconds