ANSI SCTE 62 pdf free download
ANSI SCTE 62 pdf free download.Measurement Procedure for Noise Figure.
8. Procedure 1. With the DUT connected into the setup and powered, allow time for the DUT to warm up and stabilize before making measurements. 2. Set the ANFM according to the manufacturer’ s instructions for measurements at the desired frequencies. Generally, the measurement mode selected will be corrected NF. In this mode, the system calculates the DUT NF from measurements of uncorrected NF and DUT gain. The concept is explained in Appendix 1 – Uncertainties and Corrections. 3. If desired, an oscilloscope (connected to the ANFM outputs provided for that purpose) can be used to graphically display the variation of NF and gain versus frequency. Also, a measurement of uncorrected NF can be made to show the magnitude of the correction being made for second- stage noise. 4. Record the test results. A suggested format is given in Appendix 5 – Test Report. Appendix 1 – Uncertainties and Corrections The modern ANFM makes measurement very quick and convenient. However, in order to properly evaluate the results, some knowledge of the sources of error and means to minimize them is necessary. To begin with, we should differentiate between avoidable and unavoidable errors.
One class of avoidable errors results from poor setup conditions. A noisy environment and inadequate shielding can allow extraneous signals to pollute the measurement. An oscilloscope connected to the ANFM scope / recorder output will usually show this. Before resorting to the ultimate solution of a shielded room, the integrity of all connections and quality of cables should be checked in order to eliminate or minimize the problem. Dirty or worn items can cause signal loss or intermittent readings, and must be cleaned or replaced. Another avoidable error stems from the fact that the noise figures of many devices vary with source impedance. Since the noise source is switched between“on”and“off’ states in making measurements, its output impedance could vary and affect the reading. Using a quality noise source such as that suggested can make this effect negligible. Choice of noise source can, while not intrinsically causing errors, make certain errors more significant. As a rule-of-thumb, the noise source should have as low an ENR as practicable, but not less than about 10 dB below the expected NF being measured. (Note that this means available ENR, which is the noise source output minus the loss of an MLP.) A low-ENR (≈6 dB) avoids the possibility of overloading the DUT. Also, since some ANFMs adjust for higher input levels by adding input attenuation (thereby increasing its own NF), less second-stage correction of the measurement (see below) would have to be applied. Finally, since most low-ENR noise sources have a significant built-in attenuator, they generally have better output RL as well as more constant RL between the“on”and“off” states. On the other hand, if the available ENR is more than 10 dB below the NF of the DUT, there will be so little difference in DUT noise output between the source“on”and“off’states that measurement accuracy of the ANFM itself will be compromised.ANSI SCTE 62 pdf download.
