noise rating
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the_man_one said:
Simply put, Noise Ratio (NR) is a measurement of the amount of noise generated in the amplification of a satellite signal.
Beware..... In recent years, the stated NR specification is incorrect on the majority of consumer off-the-shelf LNBFs. 0.1, 0.2, 0.3 noise ratios with a low cost, mass produced LNBF are marketing "fibs".
Sorry to quibble, but this isn't entirely correct.
Even a 'perfect' LNB will exhibit thermal noise, which is easily calculated. This represents a lower bound on what can be achieved in the real world. A real world LNB will always produce more noise than this amount. The usual definition is normally said a little differently, but a Noise Figure (NF) rating provided for Ku LNBs is the difference (in dB) between the actual noise power of the LNB and the theoretical limit of noise power. C-band LNBs are usually specified in noise temperature, which is just another way of stating this.
I would tend to agree the NF ratings of most LNBs are dreams at best and lies at worst. In fairness, for practical reasons such specifications are usually provided as nominal values for a large population of units, rather than a maximum value that will never be exceeded. A few days ago I published a short piece here on how much variation there can be across the frequency band. I've toyed with doing a more explicit test that would plot NF vs. frequency and compare this to the individual test curves provided with some LNBs. That could be quite ugly.
Even a 'perfect' LNB will exhibit thermal noise, which is easily calculated. This represents a lower bound on what can be achieved in the real world. A real world LNB will always produce more noise than this amount. The usual definition is normally said a little differently, but a Noise Figure (NF) rating provided for Ku LNBs is the difference (in dB) between the actual noise power of the LNB and the theoretical limit of noise power. C-band LNBs are usually specified in noise temperature, which is just another way of stating this.
I would tend to agree the NF ratings of most LNBs are dreams at best and lies at worst. In fairness, for practical reasons such specifications are usually provided as nominal values for a large population of units, rather than a maximum value that will never be exceeded. A few days ago I published a short piece here on how much variation there can be across the frequency band. I've toyed with doing a more explicit test that would plot NF vs. frequency and compare this to the individual test curves provided with some LNBs. That could be quite ugly.
The "WHY is it important" part. The lnbf delivers a data stream to the receiver to demodulate and decode. If the datastream is relatively clear of noise and is largely valid data, then the Quality of the signal will be higher than a datasteam that is more noisy, and therefore it is more difficult to discriminate the data from the noise resulting in a lower quality signal. That's my guess, anyway.
thanks for the replies.... now next question is a primestar (popcan) lnb good or are there better ones out there?
I'd say it's good. You COULD probably find an Invacom that might be better, but the Primestar original lnbf's were better than many you can buy today. Doesn't it have separate connections for H and V polarity, so you'd want to put a 22khz switch on it , to select polarity. That might be a factor in buying a new lnbf , rather than the original, depending upon your system setup.
A 2 x 4 (or, more commonly, a 3 x 4) multiswitch is probably the best choice for the P* LNBs with the separate H and V outputs. Your local Radio Shack might have a few left on clearance for $9.99.
Did I just recommend Rat Shack?
Did I just recommend Rat Shack?
The DishStore, one of our gold sponsors , has some in their Bargain Bin for $5 plus shipping. DISHSTORE.NET : Eagle Aspen/ Zinwell 3x4 MultiSwitch - $5.00 .
Well, the ones with dual outputs are useful in that they allow you to use multiple receivers with them (provided you use a multiswitch). The single output ones can only feed one receiver (unless you use the loop through on the receiver, which has its limitations)...
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