data comparison and noise measurement

[taupune]

Hi,
I would like to measure the signal noise in a tv cable after introducing a splitter and compare it with the original signal.

Keeping in mind the bandwidth frequency of the tv cable signal transmission, what kind of instrument do I need? Oscilloscope perhaps??? At what speed? I dont know yet the cable info, but I am searching for it and trying to make sense out of all that jargon.



Thank you

[Fish4Fun]

taupune,

Yes, a DSO (Digital Storage Oscilloscope) would be the right answer. For a "good test", you will need a two channel DSO. Depending on the frequency range you are interested in this may be a rather serious investment. A DSO capable of accurately analyzing noise in a 7mhz to 1Ghz signal is a fairly high-tech piece of equipment. Lecroy makes some nice scopes in the > 1Ghz frequency range, and they are everything except cheap. If you are only interested in the lower frequency channels, there are some very decent scopes available for orders of magnitude less money. You can find fairly decent DSO's with bandwidths < 100mhz for less than $1000usd. To get > 1Ghz scopes you are looking @ $20k+.

While I think a DSO is an essential part of a good hobbyist's tool kit, looking @ analog or digital cable signals is pretty mind-numbing unless you have some specific purpose in mind. It might be a good idea to simply state what you are attempting to do (If you want the SNR of a cable splitter, it should be plainly written on the package, or available from the MFG, so I am assuming this is NOT what you are truly after.)

Fish

[taupune]

I want to put an amplifier right after the cable splitter and see what will I get. Will I get better signal compared to the datasheet or no.
I checked on digikey and they had opamp in the commercial amplifiers for only a few bucks.

So yeah, I want the SNR but of my own homemade device.
I will see if I can find ony digital storage oscilloscope laying around my basement ( I meant school labs :) )

[f95toli]

This is the type of measurement that can be as difficult or as "easy" as you want. You can't use a DSO to "properly" measure noise, for that one usually uses a spectrum analyser. You also have to decide what "kind" of noise you want to measure (phase noise? Or are you looking for the SNR)), another important parameter is the distortion.

Noise measurements are very tricky, and in order to do it properly you need the right tools and quite a bit of knowledge.

[taupune]

You also have to decide what "kind" of noise you want to measure (phase noise? Or are you looking for the SNR)), another important parameter is the distortion.


What type of noise is created by adding two cables together with a splicer?
I think I need SNR, dont I?
I have been reading a book about cables but its really deep and thick one. it can be probably used for graduate studies. There is too much info in it.

If i put an amplifier would it create any phase distortion?

Thank you f95toli.