Why does further amplification of a TV signal actually cause the picture of a specific channel (#2) to worsen?

Question

I have a Philips 50db amplified antenna. I was setting it up with full amplification, and the picture on channel 2 (our weakest signal) was poor: bright squiggly lines running horizontally across the screen. Once I reduced the amplification from 50 db to 40 db the picture was much improved. How is one to know, short of trial and error what setting will be the best?

Answer 1

a lot of wrong answers.

your problem is cross modulation. Your amplifier is taking in ALL the channels and amplifying them equally (sort of).
If u have a strong signal it gets amplified as much as the weak one.

When ALL these amplified signals hit the tv the very strong channel overloads the tuner and causes adjacent channel interference. The channel getting interfered with is not necessarily adjacent to the strong one, it has to do with conversion and IF frequencies.

What u need to do is either amplify just the weak channel by using a bandpass filter or attenuate the strong interfering channel before the amp.

I lived near channel 9 and it overloaded everything and the local parts place had lots of channel 9 filters.

it will do that with cable channels also. And strong OTA channels will interfere with cable channels too.

when u dropped the gain of the amp u got the strong signal low enough to eliminate the problem.

Channel 2 seems to be the one getting beat up all the time.

Is your strong channel 5 per chance. Most cable companies don't use ch 5 because of that.

On the other side, more is not better. there is a science to it.

U can't take a bad signal at the antenna and make it good with an amplifier. The amplifier will negate loses in splitters, cable, coupling, etc. but if the signal at the antenna isn't snow free, it won't be snow free in the living room.

if u have 100 feet of cable with a 10db loss at the highest freq channel (research the loss/foot of your cable at you highest freq channel) and a 4 way splitter, your amp should be set at 19db gain, 10 for the cable and 9 for the splitter. I would add 2-5 more just for grins. 2 way is 3 DB loss.

that will give u the same picture u would get with a few feet of cable direct from antenna to tv.

Bottom line, your amp is probably way overkill for your app

Answer 2

>Once I reduced the amplification from 50 db to 40 db the picture was much improved. How is one to know, short of trial and error what setting will be the best?

No there isn't.

There are two likely causes for this confusing result:

1. All amplifiers cause additional noise in the signals that they amplify. It may be that when you set the amp at its maximum gain, it adds a lot more noise. An analogy would be if you listened to classical music using a small speaker a normal volume, and then hooked it to an amplified that sent 8 times (+ 9 dB I think) its rated power into it. The sound would be pretty distorted (before the speaker blew out).

2. It may be that at 50 dB, the tuner in your TV is being overloaded by too high of a signal. Sending a receiver too high of a signal will cause the signal to be distorted.

If you had enough training in electronics (and equipment), you could predetermine this, but for ordinary people, trial and error is much easier.

--------------------------------------------------
Additional Info.
One of the other answers refers to cross modulation. This would be a particular type of #2 above.

A TV tuner has to sort out the signal you want from all the other ones. Since your Philips amplifies all the signals, it could amplify another (stronger) channel enough to overload the tuner, this can cause part of the stronger signal to spill over/mix with the channel you want.

Answer 3

You are asking about waveform field propagation and signal entropy HERE where mostly TV repairmen hang out?

Problem is there are several factors that are responsible for the way a Modulated transmission reaches a receiver the way that it does. To complicated and lengthy for this forum.

Short of a Masters Degree in Electrical Engineering, and several thousands of dollars in test equipment your best bet is trial and error.

A amplifier just amplifies a signal, it offers no additional attenuation. I does not surprise me that you had this kind of issue.

Answer 4

That's it. Trial & error.

If a signal is weak, then your TV doesn't have much to process or work with. An antenna amplifier can give it more. Too much, though, and the amplifier is also amplifying all the extraneous interference picked up along the way. When that becomes too high, the TV thinks it's important and tries to process that, as well.

Answer 5

Unfortunately signal amplifiers will boost a good signal more but has the opposite effect on a channel that is not coming in that good.

Answer 6

Gain is something that needs to be tooled with. For example, on a guitar amp, if you turn the gain all the way up, the signal just gets muddy and useless, you usually have to turn the gain to halfway and then turn the volume up. So you see, more gain isn't always the answer.

Answer 7

Sebelius served as Kansas' coverage commissioner until eventually now starting to be governor. DeParle until eventually now served as commissioner of the Tennessee branch of Human centers and worked interior the workplace of administration and funds throughout the time of the Clinton administration (Fletcher, Washington submit, 3/3). additionally throughout the time of the Clinton administration, DeParle oversaw Medicaid and Medicare because of the fact the administrator of the wellness Care Financing administration, now CMS (Pear/Zeleny, manhattan cases, 3/3). DeParle at the instant is the handling director of inner maximum fairness agency CCMP Capital, and he or she serves on the boards of quite a few companies on the subject remember of wellness care. A White homestead spokesperson suggested that DeParle is interior the flexibility of resigning those posts. The Washington submit comments that "Sebelius and DeParle would be charged with helping to craft and sell the administration's formidable attempt to redesign the rustic's wellness care equipment and strengthen get admission to to the 40 six million human beings interior the rustic who lack coverage, mutually as attempting to rein in runaway costs" (Washington submit, 3/3). in accordance to the Tennessean, mutually as Sebelius will "lead the day by day administration of Medicare, Medicaid and different federal social and wellness care classes," DeParle "stands out as the president's wellness coverage counselor"T his us of a is going to hell!

Answer 8

you can go to radioshack and they have a sensor that you can connect to the coax and it will have a needle where you can see the optimal signal strength. Of course, you could save yourself 50-70 bucks and just eyeball it.

Answer 9

Advanced electronics training and a 1000 dollar OC. Scope should do the trick, what you are probably experiancing is clipping and it is ony noticable on a scope.