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3D TV, High Definition Television, HDTV 4K and AV
HD, 4K TV and Receivers
Decibel accuracy TM5402 M3 \ E2 STB's \ Sat meters.
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<blockquote data-quote="s-band" data-source="post: 1126682" data-attributes="member: 407744"><p>Those figures are calculated by the demodulation process not from RSSI. Their relationship to the actual signal level is complex. e.g. if the phase noise of the LNB is poor the SNR will be reduced. This would be especially so for narrow signals. Fractions of a dB SNR variation are not really important at high SNRs due to the law of signal level vs SNR. At high levels you may need 3dB extra RF signal to get 1dB improvement in SNR. There will be a point were the SNR doesn't get any better. This plot was done years ago on a 30W TP and shows the SNR reaching a limit at around 18dB. You can see that it would be best to use a lower SNR TP to tweak a system.</p><p>[ATTACH]141179[/ATTACH]</p><p></p><p>I would expect a dB or so spread between receivers so the <1dB difference, at 18dB SNR, is insignificant. The important thing is the point at which you lose lock. A simple signal generator can't be used to check these values. You'd need a vector signal generator and set up for the actual modulation you're interested in but it's not worth the cost/effort for our purposes. The simple way is to turn the dish, to reduce signal, and see how the receivers track.</p><p></p><p>[USER=178786]@moonbase[/USER] is best equipped to compare receivers as he has a decent dedicated meter. </p><p></p><p>Here are a couple of related links:</p><p><a href="https://headendinfo.com/ber-mer-digital-headend-system/" target="_blank">BER MER OR BIT ERROR RATE MODULATION ERROR RATIO</a> (QAM related but the principle is similar)</p><p>[URL unfurl="true"]https://www.rohde-schwarz.com/file/n178_snr-mer.pdf[/URL]</p></blockquote><p></p>
[QUOTE="s-band, post: 1126682, member: 407744"] Those figures are calculated by the demodulation process not from RSSI. Their relationship to the actual signal level is complex. e.g. if the phase noise of the LNB is poor the SNR will be reduced. This would be especially so for narrow signals. Fractions of a dB SNR variation are not really important at high SNRs due to the law of signal level vs SNR. At high levels you may need 3dB extra RF signal to get 1dB improvement in SNR. There will be a point were the SNR doesn't get any better. This plot was done years ago on a 30W TP and shows the SNR reaching a limit at around 18dB. You can see that it would be best to use a lower SNR TP to tweak a system. [ATTACH]141179[/ATTACH] I would expect a dB or so spread between receivers so the <1dB difference, at 18dB SNR, is insignificant. The important thing is the point at which you lose lock. A simple signal generator can't be used to check these values. You'd need a vector signal generator and set up for the actual modulation you're interested in but it's not worth the cost/effort for our purposes. The simple way is to turn the dish, to reduce signal, and see how the receivers track. [USER=178786]@moonbase[/USER] is best equipped to compare receivers as he has a decent dedicated meter. Here are a couple of related links: [URL="https://headendinfo.com/ber-mer-digital-headend-system/"]BER MER OR BIT ERROR RATE MODULATION ERROR RATIO[/URL] (QAM related but the principle is similar) [URL unfurl="true"]https://www.rohde-schwarz.com/file/n178_snr-mer.pdf[/URL] [/QUOTE]
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3D TV, High Definition Television, HDTV 4K and AV
HD, 4K TV and Receivers
Decibel accuracy TM5402 M3 \ E2 STB's \ Sat meters.
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