ANSI SCTE 126-2019 pdf free download – Test Method for Distortion of 2-way Amplifiers Caused by Insufficient Isolation of Built in Diplex Filter.
7.4. Determination of Correction Setup Constant (csc)
In order to get accurate readings during measurements, the insertion loss of the test setup from point“A”to the spectrum analyzer must be known and if an internal amplifier is used, the gain of the internal
amplifier must be known.Inserting a known signal at the point “A”and reading the level of this signal onspectrum analyzer can determine this. The following procedure can be used:
7.4.1. Connect the signal generator directly to the spectrum analyzer; adjust signal generator
frequency to the Cw carrier second harmonic frequency of interest.
7.4.2.Adjust spectrum analyzer as described in 7.3.2, except with a center frequency set to the
Cw carrier frequency second harmonic of interest and Internal Amplifier “OFF”.7.4.3. Adjust the signal generator level to get a reading of -30 dBmV on spectrum analyzer.7.4.4.— Apply this level from the signal generator to the 6dB attenuator at point “A” of the test
setup in Figure 2. With the spectrum analyzer adjusted exactly as described in 7.3.2, butwith the center frequency set to the Cw carrier frequency second harmonic of interest,read the measured power value. If the internal amplifier is being used, make sure it is on.
7.4.5. The difference between the value read and -30 dBmV is the Correction Setup Constant
“CSC”, and must be used in calculations of second harmonic distortion.
CSC[dB]=-30 dBmV – Value read [dBmV]
7.4.6. Determination of the test setup correction constant can be done at different frequenciesif there is a suspicion that the response of diplex filter and or optional filters varygreatly between the Cw carrier frequency and the Cw carrier frequency secondharmonic.
8.Test Procedure
8.1. Connect equipment as specified in Figure 2.The signal Power Level “PL ” must be adjusted as
specified in paragraph 7.3.1.
8.2. Adjust the signal generator to the test frequency and the spectrum analyzer to the same setup as
described in 7.3.2
8.3. Use the “Peak Search”function of the analyzer to read the Second Harmonic Level “SHL”.
The”SHL” must be corrected using the Correction Setup Constant determined in 7.4.5
CSHL [dBmV] =SHL [dBmV] +CSC [dB]
In case the CSHL level is 10 dB or less above the noise floor of the spectrum analyzer, do the following:Record the Noise Floor Level as the level of the noise floor in a flat portion of the spectrum displayed onthe SA.
Compute Noise Floor Delta =CSHL Level -Noise Floor Level. If the Noise Floor Delta is less than 2dB, it is recommended that the optional post-amplifier be added to the system. The measurement shouldthen be made again. If, however, the Noise Floor Delta remains less than 2 dB, refer to ANSISCTE 96
A table of values calculated from this equation is presented in ANSI/SCTE 96 2013, Section 8.2.
Compute Corrected CSHL as:
Noise-adjusted CHSL = CHSL + Noise Floor Correction Factor
8.4. For comparison reasons, it is important to also calculate the relative value of Second Order Distortion (SOD) with reference to input Power Level (PL) as follows:
SOD [dBc] = PL [dBmV] – CSHL [dBmV]
Use either CHSL or Noise-adjusted CHSL as appropriate as calculated in section 8.3
8.5. Suggested test frequencies, power levels, and recording tables are described in section 10,
“RESULTS RECORDING, TEST FREQUENCIES AND LEVELS”.ANSI SCTE 126 pdf download.