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Distinguished From Traditional Eb/No Instruments CNG instruments are used in a wide range of applications. Commonly noise is added at intermediate frequency (IF) including 70/140MHz and L-band Satcom testing noise is also added at radio frequency (RF) in the case of CDMA phone and base-station testing and even at baseband often when complex DSP algorithms are used such as for digital beam-forming systems. There are several attributes where Micronetics' CNG instruments distinguish themselves from traditional Eb/No boxes. These are detailed as follows:
Eb/No Accuracy: Figure 2 shows several different theoretical curves corresponding to different modulation formats. What is striking is that a fairly small amount of Eb/No uncertainty translates into a large uncertainty of bit error rate due to the steep slope of the theoretical curves as depicted by the shaded area. This is the reason Micronetics' design architects would not compromise on the accuracy, repeatability and stability of Eb/No. At the heart is a sophisticated power measurement system able to accept complex time variant amplitude and crest factor signals such as 7/8 coded QPSK and 256 QAM. This power measurement system is crucial for accruacy.
Built-in Calibration: Micronetics' CNG instruments have built-in calibration functions which can be performed by a keystroke or remote command at any time. Other Eb/No boxes can only perform these by hand during the annual factory calibration. The two primary routines are:
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Intro Page The Micronetics Difference The Micronetics Difference cont.
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Figure 1 is a block diagram of a typical satellite modem loop test set up. This set-up benchmarks the demodulator against its theoretically ideal performance of BER vs Eb/No. The CNG instrument sets up the Eb/No and a communication analyzer measures the bit error rate. Plotting BER vs. Eb/No produces what is known as a waterfall curve due to its shape when plotted on a log/log graph.
