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Fringe Reception General
0.01dB lnb?
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<blockquote data-quote="Llew" data-source="post: 192239" data-attributes="member: 175007"><p>Hmm - I wonder if SMW are still using the HP8970B Noise Figure Meters that they tested their LNB's with back in the early '90's? This had a measurement uncertainty of +/- 0.3dB.</p><p></p><p>Quote from their 1996 catalogue -</p><p></p><p><u>Measurement Uncertainties</u></p><p></p><p>"Despite the use of advanced measurement equipment you will still have some uncertainties to consider. There is an instrument uncertainty in the Noise and Gain analyser of +/- 0.3dB, the noise source has an uncertainty of +/- 0.07dB and there is a mismatch uncertainty of +/- 0.1 dB. This gives a worst case uncertainty of 0.2 dB or a RSS (Root Sum of Squares) of 0.12dB.</p><p></p><p>But this is however not all. There is another source of error which few people are aware of. The noise source impedance changes slightly between the "cold" and "hot" state resulting in that the LNB "sees" a difference in impedance at the input. This change in impedance does affect the gain of the LNB which also changes with the "cold" and "hot" state of the noise source. This causes the LNB to change the NF and, what is worse, the gain of the LNB during the measurement. Since the analyser measures the ratio between "cold" and "hot" state this can result in a significant error in the noise figure measurement. And this error can be up to 0.3 dB. There is however a way to reduce this error. This is to use a noise source with very little difference in the impedance between "cold" and "hot" states. There are noise sourses available with an extra 10 dB built in attenuator which reduces the impedance variation considerably."</p><p></p><p>Presumably the NF figures of the currently available SMW LNB's are based on measurements taken with these meters?</p><p></p><p>Llew</p></blockquote><p></p>
[QUOTE="Llew, post: 192239, member: 175007"] Hmm - I wonder if SMW are still using the HP8970B Noise Figure Meters that they tested their LNB's with back in the early '90's? This had a measurement uncertainty of +/- 0.3dB. Quote from their 1996 catalogue - [U]Measurement Uncertainties[/U] "Despite the use of advanced measurement equipment you will still have some uncertainties to consider. There is an instrument uncertainty in the Noise and Gain analyser of +/- 0.3dB, the noise source has an uncertainty of +/- 0.07dB and there is a mismatch uncertainty of +/- 0.1 dB. This gives a worst case uncertainty of 0.2 dB or a RSS (Root Sum of Squares) of 0.12dB. But this is however not all. There is another source of error which few people are aware of. The noise source impedance changes slightly between the "cold" and "hot" state resulting in that the LNB "sees" a difference in impedance at the input. This change in impedance does affect the gain of the LNB which also changes with the "cold" and "hot" state of the noise source. This causes the LNB to change the NF and, what is worse, the gain of the LNB during the measurement. Since the analyser measures the ratio between "cold" and "hot" state this can result in a significant error in the noise figure measurement. And this error can be up to 0.3 dB. There is however a way to reduce this error. This is to use a noise source with very little difference in the impedance between "cold" and "hot" states. There are noise sourses available with an extra 10 dB built in attenuator which reduces the impedance variation considerably." Presumably the NF figures of the currently available SMW LNB's are based on measurements taken with these meters? Llew [/QUOTE]
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0.01dB lnb?
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