Ceton InfiniTV amplifier

[Crash2009]

We have been working on a pixelation issue over in HTPC Components. Assume for a moment that we have a coax line connected to an InfiniTV directly from the pole. What we are trying to calculate is the signal strength of the incoming line. Here is a screencap of the scenario.

What is the signal strength of the incoming line, and How do we calculate it?

[JohnW248]

Your signal strength is in the second column. It is expressed in dBmV where the perfect signal would be 0 dBmV. Generally a range of +/- 7dBmV will give you good results. The next column shows your signal to noise level. Here the higher the number the better with a basement of around 34 dB

There are other causes of pixelation that are not shown by these numbers. If there is broadband noise on the drop there can be interference across several channels.

As a test start FOUR recordings at the same time. Write down the frequency for each channel and then watch a channel for an error. Note the time and then play another recording to the same point and see if you have a problem. That would show a broadband interference. Individual channels may have problems that ride in and out of the cable headend, for example an uplink problem and maybe even something with the original program material.

You also notice a lot more trouble when we hit the Solar Spot season twice a year which has an impact on all sat reception.

If you see broadband problems, this is a job for the cable comopany which would start with a full spectrum scan on your signal and then working back to the splitter on the pole to the node, to the fiber to the headend to the sat receiver and so forth. It would also be possible to introduce problems in the qam tanks when the channels are mixed and encoded for their ride on the coax/fiber.

[Crash2009]

There is always more to it than meets the eye.

Thanks for the test procedure. I will run that prior to my cable appointment.

To be more specific about the question we have, and assuming there is some kind of amplifyer/splitter arrangement within the Infini4, Is it possible to calculate the strength of the cable signal on the way in, based upon the measurement of the signal on the way out?

I understand there is some conflicting information out there, and was just trying to help clarify it.

[maximus4]

i have some crazy signal strengths as well, and i spent quite some time trying to get an answer to this. some people thought there was an internal amp and some didnt and it ended up exactly how your diagram looks. i believe the problem lies in the question marks lol

[STC]

Different channel frequencies will have different signal strengths. Set all tuners to the same channel, then measure.

[JohnW248]

There is always more to it than meets the eye.

Thanks for the test procedure. I will run that prior to my cable appointment.

To be more specific about the question we have, and assuming there is some kind of amplifyer/splitter arrangement within the Infini4, Is it possible to calculate the strength of the cable signal on the way in, based upon the measurement of the signal on the way out?

I understand there is some conflicting information out there, and was just trying to help clarify it.

Note the frequencies for your signal levels. Both the high output are in the same QAM tank and both the low numbers are in a higher frequency QAM tank. For fun when you get this reading, switch around the four channels you're using and see if the signal levels move with the channels or stay with the tuner alignment. I find that they move with the channel not with the tuner. For example if I have a channel that is always lower output, it will have lower output no matter which tuner it is on. In fact you can tune each tuner as STC said to the same channel and that will reveal any signal variation within the device. In the four tuner design it is really very close.

[richard1980]

To clarify the OP's question (we were discussing this in a different thread), if the InfiniTV web page reports a specific signal strength for a specific frequency, how can you derive the signal strength for that frequency on the incoming line (before it gets split by the InfiniTV)? In short, does the InfiniTV contain an amplifier, and if so, what amount of amplification does it produce?

There are posts by erkotz that state there is an amplifier, but I have yet to find any post that tells how much amplification it offers. Additionally, there are some users that claim their testing reveals there is no amplifier. My own testing indicates there is an amplifier although I'm not sure if my method of testing is correct. (I compared the signal strength reported by my cable modem to the signal strength reported by the InfiniTV web page, both measured at 855.000 MHz, and the InfiniTV web page reported a net gain of 1 dB at the individual tuner, which I assume means there is an 8 dB amplifier onboard.)

With all due respect to the non-Ceton users, I would appreciate an official answer from Ceton.

[crawfish]

To be more specific about the question we have, and assuming there is some kind of amplifyer/splitter arrangement within the Infini4, Is it possible to calculate the strength of the cable signal on the way in, based upon the measurement of the signal on the way out?

Sure, you just account for the losses due to splitters and gains due to amps. For more accuracy, you would also need to account for the length of the cable run. Presumably the Ceton has an internal 4-way splitter you need to account for, which should mean adding 7 dBmV to the signal strength it reports for a given channel. There can be a significant decrease in signal strength as you move from lower frequencies to higher frequencies, which you've observed. This is normal according to my cable provider, and it increases with cable run lengths.

For example, if your device with internal 4-way splitter is reporting 0 dBmV for a given frequency, you would calculate its input signal as +7 dBmV at that frequency. If it is being fed by a 2-way splitter, that splitter's input would be an additional 3.5 dBmV higher, or +10.5 dBmV. And so on.

ETA: This calculation will of course be relative to whatever device you take the signal level from. Using my SB6120 as the basis, my HDHR Prime measures about 6 dBmV lower than expected at the same frequency. I'm actually averaging channels at 651 and 753 MHz to approximate my cable modem at 700 MHz; this seems valid as the signal strength loss varies linearly (R^2 = 0.97 with 10 data points) from 75 MHz to 813 MHz on the Prime. I'm unable to explain this discrepancy. The Prime and modem are on the same 2-way splitter with the only difference being the tuning adapter between the Prime and splitter, which I accounted for, and it's not the splitter. I'm assuming both the modem and Prime have an internal 4-way splitter and are comparable WRT how they report signals. The 6 dBmV difference is in between the loss due to a balanced 3-way splitter (-5.5 dBmV) and a 4-way (-7 dBmV), but I've accounted for all the splits I know about. I guess the modem could be reporting the signal strength before its internal split, making my starting value artificially high by just about the right amount to agree with the Prime's values. Or maybe the SB6120 has an amp to negate its internal 4-way split. Or the Prime could have extra signal loss beyond the presumed internal 4-way splitter, but that seems unlikely.

[maximus4]

i have been plagued qith a wall reading of -0.5db and all four tuners reporting almost -20db (even with all splitters and other stuff removed) , the cable company says all is fine and naturally wont touch the computer set-up. some say i shouldnt need an amp, but most all say -20db isnt good enough, and where all this loss is coming from is anyones guess, i think with these numbers there is no way it can have one, but yeah id like an official answer too just to help my amateur cable frequency math. symptom is countless no tv signal errors btw.