Amplification Question

BobHaskett · 19-Mar-2013, 3:27 PM

I have two scenarios I have been testing for the last week or two. Which one would you prefer? The first is a 8275 Preamp to a Passive 8-Way Splitter. The second is a 8275 Preamp to a CM3418 distribution amp. Both scenarios produce the same signal results. Is there any benefit to leaving the extra amp in the mix if the signal is not boosted in any way?

ADTech · 19-Mar-2013, 4:41 PM

No, except to your electric company.

GroundUrMast · 19-Mar-2013, 5:52 PM

My preference is to use the simple, clean design. Each amplifier adds a small amount of noise and distortion, though in you case, not enough to cause visible signal degradation. The preamp is in the best location to do what amplification is supposed to do, overcome the losses in coax and splitters. I would ditch the CM-3418... It's not contributing to reliable reception, and may be a source of needless trouble if a new TV of FM station comes on line.

BobHaskett · 20-Mar-2013, 1:07 AM

Thanks. I actually just found a 6-Way Passive splitter on Amazon. I could not find them locally. I am going to see if dropping the un-needed ports helps any. Even though they are terminated.

GroundUrMast · 20-Mar-2013, 3:14 AM

Are you having trouble with a desired signal? Or is this an attempt to maximize signal meter readings?

BobHaskett · 20-Mar-2013, 4:34 AM

Quote:

Originally Posted by GroundUrMast

Are you having trouble with a desired signal? Or is this an attempt to maximize signal meter readings?

Maximize signal. I have one channel (PBS) that I could not receive until I switched to a 7694 and a stronger preamp (from a CPA19 to a 8275). I now get PBS at a 52 signal strength, bute the signal strength now drops occasionally during windy/rainy days. Not a huge deal, not something I would install a larger antenna for, but I was trying a few things to see if I could make it a little stronger.

GroundUrMast · 20-Mar-2013, 7:11 AM

Generally you'll find the most effective location for an amp is at the antenna. That's because an amplifier can only overcome the losses and noise issues of components on the output side of the amp. Amplifiers do not / can not 'pull' signal from the antenna, cable or air. If you don't have a good signal from the antenna, you'll only amplify the noise and low quality signal. Making it a noisy low quality signal more powerful is not an improvement, amplified noise is not going to help the tuner recover error free data. Then to make matters worse, even the best amplifiers add a bit more noise of their own.

Most digital TV signal meters offer some indication of signal quality... usually based on digital error rate rather than signal power level. So once you have added enough amplification to overcome the losses and tuner noise figure in your system, you'll see little if any additional improvement in meter readings. So there's little to be gained from amplifier gain in excess of the sum of cable losses, splitter losses and tuner noise figure. In fact excess gain invites distortion that interferes with reliable reception.

Bottom line, reliable reception is primarily a function of the antenna choice and it's location. Antenna gain is better than amplifier gain.

BobHaskett · 22-Mar-2013, 2:08 AM

Quote:

Originally Posted by GroundUrMast

Generally you'll find the most effective location for an amp is at the antenna. That's because an amplifier can only overcome the losses and noise issues of components on the output side of the amp. Amplifiers do not / can not 'pull' signal from the antenna, cable or air. If you don't have a good signal from the antenna, you'll only amplify the noise and low quality signal. Making it a noisy low quality signal more powerful is not an improvement, amplified noise is not going to help the tuner recover error free data. Then to make matters worse, even the best amplifiers add a bit more noise of their own.

Most digital TV signal meters offer some indication of signal quality... usually based on digital error rate rather than signal power level. So once you have added enough amplification to overcome the losses and tuner noise figure in your system, you'll see little if any additional improvement in meter readings. So there's little to be gained from amplifier gain in excess of the sum of cable losses, splitter losses and tuner noise figure. In fact excess gain invites distortion that interferes with reliable reception.

Bottom line, reliable reception is primarily a function of the antenna choice and it's location. Antenna gain is better than amplifier gain.

Great info. Thanks.

Last question...When using, say, a 6-Way splitter. Is there any difference in terminating the unused ports on the actual splitter connection vs. connecting a coax with no TV attached?

I have a 6-Way passive splitter at the moment. Each split goes to a different room in the house. We do not yet have TVs (but will eventually so I went ahead and ran the coax) in 3 of the rooms. Would it be fine to leave the coax connected to the splitter? Or should I go under the house and terminate the unused ports until we get a TV for those rooms?

GroundUrMast · 22-Mar-2013, 6:09 AM

An unterminated coax reflects the signal back into the splitter. This adds a source of short-path multipath interference that the connected tuners will need to deal with.

Best practice is to terminate unused ports. That can be done at the splitter or at the far end of the cable. I would opt to place the terminator at the coax wall jack if you anticipate using the jack at some point... save the trip back under the house.