Quote:
Originally Posted by HD-man
...... Now, I have another question for you expert folks. What is the best LNBF that you can get presently. I saw one with 0.4 dB noise is this a good one or should I select another one. Thanks again for your help.
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This is an interesting question, and I don't think there is an easy answer that will be useful. Relative to what LNBF is "OK", then virtually anything that you buy new, will probably work OK.
As others have said, lower noise is good, but I had been using LNBs that were up around 0.8 or 0.9, and had no problem at all, and I think even now, I'm only using an lnb that's around 0.7, so while a low noise figure is good, for 95% of the signals up there, it probably isn't that important. However if you are trying to get a very weak transponder, then having a problem, then having a low noise figure might just make the difference.
However the noise figure isn't the only thing important. Other factors that are important are gain (amplification), phase noise, and frequency stability. The problem with these LNBFs is that all you see in the product descriptions is the noise figure. I recently (1 and 3 years ago) replaced my Ku and
C-band LNBs. The main reason I "upgraded" was that the LNBs I had were about 10 years old, and their frequency drifted a lot. With a DCII receiver, you can watch the diagnostic screen, and see how much the receiver is having to shift the frequency to follow the drift of the LNB, and in my case it was often over 2 MHz, and sometimes as much as 3 MHz! On a broad signal, ie one with a high SR, this wasn't very important, but on very narrow signals, ie signals with SR values down around 2000 - 3000, this meant that if the LNB had drifted significantly, the receiver sometimes wouldn't even see the signal until the lnb drifted back to where it was supposed to be.
So when I bought a new LNB, I looked up the specifications and found that there were lnbs with drift specifications all over the place. I found LNBs with prices ranging from less than $100 (lnbs are more expensive than lnbfs for some reason), to many hundreds of dollars, up close to $1000! Those with very low drift, ie less than 0.2 MHz, were too expensive for me,so I ended up getting one with drift ratings less than 1 MHz, somewhere around 0.8 if I remember right, and that was still affordable.
If you look up the specs of what manufacturers refer to as digital ready lnbs, they usually refer to something like phase noise as the most important spec, more so than just the overall noise figure. I didn't get involved with this at all, because any lnb that was good in this category was just too expensive for me, and I was already getting 98% of the signals I'd try to lock.
The other parameter I mentioned, ie gain, I didn't figure would be important, however I found out that when I upgraded to a better LNB with better noise figure and better frequency stability, that I ended up with an LNB with less gain. So even though there was less noise coming in with my signal, there was also less signal. So I think that if you use noise as a comparison, you should be comparing lnbs with similar gain, or else the comparison isn't valid. Ie I get the impression that manufacturers may try to make their lnbs seem better, ie lower noise, by just decreasing the gain a little bit.
Also, all these parameters vary over the bandwidth of the lnb, and some manufacturers give you noise and gain numbers at one specific frequency which may not be representative of the performance over the whole band.
One aspect of this is that if you have a big dish system that has a feedhorn, where you only replace the LNB, you are using LNBs that are compatable with professional quality LNBs, and you have a complete spectrum of quality to select from, from cheap consumer to state of the art. However these LNBFs that are available for these small dishes are for the most part consumer items, so you don't have quite the spectrum of quality to select from.
Bottom line is that when you see a product description with just a noise figure, that really doesn't tell you very much, because different manufacturers use different methods of determining these numbers, and these numbers don't include other important parameters that affect the performance. So your choices are, either you do a lot of research, looking into the performance specs of each model lnb, trying to make decisions relative to tradeoffs where one lnb might be better in one respect and worse in another respect...... or .... just see what other people are using, and or what is available from respected dealers.
In other words, I don't know the answer, and I don't think you'll find an answer. But I wouldn't use just noise figure as if it were the only measure of quality. I'd almost think price was a more important measure.