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Discussion Starter · #1 ·
I put up a Channel Master 4248 this weekend and it's doing a pretty nice job. However the local CBS affiliate that broadcasts Hi def is lower power till at least the end of the year. I'm only getting a 40 on her so I get alot of breakup. I'm thinking of adding either a Winegard or Channel master amp. The Winegard is 28db, the CM is 26db but with a lower noise ratio. In this instance am I better served in going for the Higher DB? Is Noise not really an issue with Digital Television?
 

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I would suggest a titan 7775 by channel master. It works great.


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PeterDz
 

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Quote:
Originally posted by Bob Smith:
Exceptions are where the amplifier might overload (as may be the case with you). If there are several strong stations (all other stations are well up in the 80s or 90s), then you might be better off with no amplifier at all.
This is a real concern . . . I live about 26 miles from the local transmitters and I set up this monster Winegard antenna: http://www.starkelectronic.com/wca8098.htm

with this super pre-amp:

Winegard AP-8275 http://www.starkelectronic.com/wpreamp.htm


Well, at only 25 miles out, that monster antenna overloaded the pre-amp such that channels 2-6 completely distorted. Higher channels were also distorted but viewable. After taking the pre-amp out of the system, it worked properly. It is sure an ugly antenna but I get a rock solid signal of everything broadcast off of Sutro.
 

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That's a serious issue with preamps. Not only did you have all the UHF/VHF stations overloading, but you also had the multitude of FM stations in the area loading the front end. With a high gain antenna and all the stations you have in the Bay Area, there is a very good chance of overload. When I lived in Los Altos, I used only a UHF antenna Preamp combination. That way, the strong VHF/FM stations wouldn't overload the preamp.


The raw STBs, in most cases, have what is called a 'preselector' in the front end. This is an amplifier that is tuned only to the station being received, thus limiting the influence from other stations. A preamp, on the other hand, is "broadbanded", that is all stations are present at all times. This places tremendous burden on the amplifier to stay linear. The biggest problem is where most stations are strong, but the one you want is weak. In this case, the intermodulation from the stronger stations may cause spurious signals to be created with an amplitude above that of the weak station you are trying to receive. This is why removing the amplifier sometimes helps rather than hinders the received signal.


Bob Smith
 

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In about 99.99% of the cases, lower noise figure is what you want. You can't improve the signal to noise ratio once it is set by the noise in the first gain stage, more gain just means more amplified noise.


Exceptions are where the amplifier might overload (as may be the case with you). If there are several strong stations (all other stations are well up in the 80s or 90s), then you might be better off with no amplifier at all. In the case of strong stations with one weak station, you need to find an amplifier with a high "intercept point", usually they are specified as maximum input, or output, a composite signal level for all stations combined.


The advantage to a company like Winegard, Channel Master, or MATV companies like Jerrold, these things will be specified. Buying a "garden variety" Radio Shack amplifier will give you an amplifier with few specs.


Gain is much less important than noise figure and overload performance in any case. If you are already getting a signal without an amp, you don't need any gain (you are already above the cable loss) you need a low noise figure. You would probably be better off getting a higher gain antenna (free gain with 0 dB noise figure) than buying an amplifier.


Bob Smith
 

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Discussion Starter · #6 ·
With the CM 7775 Amp I went from a 40 on WFSB in Hartford to a 76 ! Now Watchable without Pixel Breakup ! I'm a Happy Guy.
 
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