40 db tv amplifier circuits
Hi,
I have designed a lot of TV cable systems, some were up to 20000 subscribers.
Let see some significant TV levels in subscruiber point:
40 dB/mkV is noisy, but enough to make good syncro.
50 dB is good enough for Black/White.
57 dB - old standard for B/W.
66 dB - minimum standard for color SECAM. I think PAL is little bit better - (64 is equivalent for PAL)
And you have to get 47 dB signal/noice ratio.
Also you need to have not more than 4 dB difference between channels in the same band. No more then 6 dB in different bands. If you have large difference then you will have some intermodulation on amplifier on cable network.
Last multibands tuners (modules) (UHF, VHF and HiperBand) are not so good at all. I think you need to add 3-4 dB for them. So, you need to have at least 70 dB in your card input. But also pay attention for some intermodulation - the upper level is near 88 - 90 dB.
You need to define what is a picture of bad channel, if it has some "snow" then you have weak signal, but if you have some thin horizontal lines on picture then maybe you have too big signal on that channel. Also you can find some floating image of neighbor channel - it is intermodulation for big difference or big level.
Maybe it is fault of your cable provider. You need to make this test: apply signal directly to some good TV-set. Look at bad channels. If they are not good at all - apply to your provider to make his service better. He must make good picture on your TV.
One solution to increase levels is to change splitter from cable system to you. As a rule they use 16-20 dB splitters, you can ask to change it to 12 (or even 10) dB splitter. So you will increase level on 6-10 dB. But maybe you have additional rf-splitter at your home, look to your cables - you can replace it or even move if second feed is not using.
Also look at your antenna socket on the wall near TV, as a rule they are using some universal socket for TV and FM signals, open your wall panel and look to the board, you will find some RCL filters there. If you will delete this circuit you will add some 6 - 10 dB too.
Good Luck! klug.