After rewatching your video on cable return Rf signals, I had a question. In my company, we want our modems’ transmit to be in a 36-50 range. Typically, if the modem transmit is low, we put an attenuator at the modem (I know, that doesn’t help with noise). So if my modem is sitting at a 32 transmit, I could put a 10 dB attenuator on to raise that to 42 dBmV. Now, to my question: Does what we are doing have any benefit to our cable plant and customer, or are we just changing signal levels to arbitrarily meet an approved range? If the modem is transmitting at 32, and that signal hits the CMTS at 0 dBmV, doesn’t adding the 10 dB attenuator leave us in the same boat? The modem transmit signal will raise to a 42, hit the attenuator, and then immediately drop back down to 32. What, if any, is the practical benefit of attenuating at the modem in these instances? And thanks again Brady and Ron for these videos!
Hi Andrew, if you are padding at the modem, you are wasting money on pads and the time to install them. It is recommended to pad at the tap instead. Padding at the tap effectively reduces noise from the subscriber's home while causing the modem to boost its transmit level. This leads to improved MER (SNR) and ultimately less noise in the return path for all subscribers on the fiber node. Please remember that a significant amount of noise can enter the subscriber's in-home wiring, particularly through the drop cable. Padding at the tap attenuates this noise. Additionally, it is ideal for the modem's transmit power to be within the range of 40-50 dBmV. Thanks for watching and best of luck to you.
The company I work for just raised their acceptable return signal to 54 dBmV. I was blown away! It went against anything I've read the past few years. My theory is that it was getting too costly to put amps in during these proactive maintenance calls with multiple CPE especially with high split coming.
@@Volpefirm To add; Putting a normal pad would drop the DS level as well and probably cause issues. Assuming we are talking about a step attenuator that has padding just on the US (5-42 MHz in most cases), placing at the tap spigot would drop all the noise generated in that house and its associated drop where 95% of the ingress comes from. (That's right, I'll end a sentence with a preposition) :) The problem with step attenuators is the specific split and could cause more grp delay as well and must be changed out when you go to 85 or 204 MHz US. A flexible solution tap with equalization is the best option, but cost, time and labor are big factors.
@@JB-tz9pi That's a bit much. I believe 48 dBmV is a good number to strive for as it gives some headroom before the CM maxes out, especially when doing 4 or even 8-ch US bonding. D3.1 CMs have more Tx power vs D3.0, but you may need some reserve when OFDMA is extended to 204 MHz eventually. Also, don't forget coax loss at higher freqs and also temperature effects.
BTW, my thought was, "DOCSIS spec" is redundant since the S in DOCSIS stands for specification. But, I do see Ron's point that you also shouldn't say DOCSIS standard. A Spec and a Standard are not the same thing. Maybe we should say the DOCSI Spec :) Or the DOCSIS doc. I also recall CMTSs are qualified, but CMs are certified.
In math the x-axis on a graph is also called domain. Time domain is when the graph has time from left to right (Oscilloscope or position vs time graph) and frequency domain is when it's frequency from left to right (SLM). 3brown1blue has a great video on Fourier transforms or FFT which is how we take a time domain reading and get it to a frequency domain.
I understand that this topic can be challenging to grasp until you have that "aha" moment. As I mentioned during the livestream, I personally found it helpful to engage in hands-on learning. If possible, I encourage you to experiment in a lab setting or with a software-defined radio (SDR). Additionally, as Josh suggested in the comment below, there are many valuable resources available on RU-vid. Thank you, Josh, for the recommendation! And thank you JB for watching! 😀
