On which of factor reflecting powers depends
Answers
Answer:
source and substance that bounces it back.
Explanation:
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Answer:
A practical example may be useful in quantizing the effects of reflected signals in typical coaxial distribution lines. Typical amplifiers and passives have return loss specifications of about 16 dB when properly terminated, with the worst performance near the ends of the passband, as can be expected. The specified directivity of taps varies as a function of both frequency and tap value. In general, the worst values are also at the extremes of the passband (especially at the low end of the upstream frequency range) and at high tap values, where the absolute coupling between ports limits the isolation. For most values, the directivity in the downstream spectrum is 10–15 dB, whereas the return band directivity is 6–9 dB. Finally, most distribution lines use cable whose loss is about 1.6 dB/100 feet at 750 MHz and varies, as we have seen, as the square root of frequency. The relative velocity of propagation for these cables is about 0.90.
Given these parameters, assume that an amplifier and two taps are spaced at 100-foot increments along a cable. At 750 MHz, the following will be the situation under proper operating conditions:
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The signal reflected from the first tap and re-reflected from the amplifier will be attenuated by 16 + 16 + 2(1.6) = 35.6 dB and delayed by 200/[(0.984) (0.9)] = 226 ns. The signal transmitted through the first tap, reflected from the second tap and coupled into the drop due to a directivity (which we will assume to be 12 dB), will be attenuated by 31.6 dB and also delayed by 226 ns. We will use this larger delayed signal for calculating the effects.
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If a digital datastream is being transmitted, one effect of this “microreflection” is that if a pulse is transmitted, an echo of that pulse will create a voltage amplitude uncertainty of about 2.6% in the signal 226 ns later.
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The amplitude response will have a “ripple” versus frequency. The frequency of the ripple will be 4.42 MHz (meaning a full cycle plus in every 6-MHz channel), and the amplitude will be 0.45 dB peak-to-peak.
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The group delay will also have a variation versus frequency at the “ripple” rate. The delay variation will be 11.7 ns peak-to-peak.
Explanation: