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RV-3090 - Amplifier Noise Figure
Date Modified: 2009-04-21

Question:
I recently purchased a new HDTV with a digital tuner. I set it up in my trailer which came with a Winegard Model RV-3090 antenna. The overall reception was not as good as it was with the previous analog TV.

I had read recently that some TV stations were not transmitting their digital signal in full strength until turning off their analog transmission. I sent an e-mail to one of our local stations asking if that was the case. The Assistant Director of Technology replied that they were transmitting digital signals full strength. He further indicated that they find that digital signals are more sensitive to noise so they discouraged the use of amplifiers. He said that if an amplifier is used, it should have a high signal-to-noise ratio.

I have looked at the Owners Manual/Installation Instructions I have on the antenna/amplifier but am unable to determine specifications on the signal-to-noise ratio. I would like to know if you have specifications on this amplifier. More importantly, I would like to know if your newest version of this antenna has a higher signal-to-noise ratio.


Tech Tip:

As stated the noise figure of the amplifier used will change the signal amount. The problem with this is unless you have a way of measuring the signal to noise level at the antenna location there is no way to calculate the signal to noise ratio of you signal at that point even if you know the amplifiers noise figure. The RV-3090’s noise figure is about 4.0dB average across the amplifiers range of 54-806MHz (channels2-69). What we're saying is that in order to have a good signal to noise ratio you need to use amplifiers with a low noise figure. The noise figure of the newer antennas may be about .2 to .3dB less which will not make that much difference in you signal to noise ratio.

As to why your picture is different with the new TV set verses the older one is it could be the sensitivity of the newer TV  may not be as sensitive as your older set was.

Engineer Response:

Technical people working within the RF world can neglect the specifics of terms and this can be misleading to those trying to understand what is being said. You are correct.  A measure of the effect an active device (amplifier) has on a signal passing through it is it noise figure.  One measure of how a signal changes as it passes through an amplifier is the signal-to-noise ratio.  Since it is a measure of change, or a "ratio", of what it is going into the amplifier and what it is coming out of the amplifier, this term would not be a specification.  The amplifier's noise figure however, allows one to predict (calculate) the change in signal-to-noise ratio as a signal passes through an amplifier.  Of course, the best amplifiers have the lowest noise figures.   
Television station engineers and electronics dealers are often discouraging consumers from using signal amplifiers because more often than not using the amplifier creates more trouble.  The most common problem is a very weak signal with a low signal-to-noise ratio and a low quality amplifier with a high noise figure.  The combination is often worse than without the amplifier.  The skill is in matching the signal level at the antenna with the right amplifier.  When done right, the results make any antenna system work well.   

It is further confusing to the consumer because recently the FCC chairman commented on the smaller DTV coverage area may require that some viewers will need a preamplifier to "boost" the DTV signal.  Since the DTV signal is lower in transmitted power as compared to the analog signal, station engineers have noted how sensitive these lower signals are to amplification so they avoid the complication of the signal amplifier.  




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