Been a couple weeks since my last update, though I'd provide insights to where things are now.
After another set of mails on Monday (17th), the Network Engineering Supervisor took a look at everything remotely (my apartment's connection and my neighbour's) and confirmed that things were hitting 31-32dB on 747MHz range (I also included screenshots in my mails to him). This was around 13:00 or thereabouts. Within 15 minutes he had the previous network/maint tech from weeks ago out here taking readings, etc..
Tech took readings at the cable box, looking at 747 and 753MHz on his analyser, and confirmed the problem. Even more interesting was that he took a reading from an open input (literally holding up the input jack in the air) and looked at what the gain was at. Normally in our area, for 73x-75xMHz, the reading is in the -40dB region. These were his readings from behind our building (I saw them myself):
735MHz = between -44dB and -46dB
741MHz = between -43dB and -46dB
747MHz = between -31dB and -37dB
753MHz = between -27dB and -33dB
Note the large jump in average gain starting at 747MHz.
The tech told me that a few weeks prior, he took readings in the same manner for every cable/line segment down Church Street (which is where our "main connection" runs to the node), and all the numbers on all the frequencies were in the -40dB range. However, when you approach this area of my block, the gain for 747MHz and above starts going off the charts. What this means is that there is absolutely
something in the air (i.e. wireless signal of some kind) that is pounding on 747MHz and above. That's perfectly fine too, but the issue (as the tech explained) is that that signal is seeping in to the node somewhere along this block -- specifically in the general line of sight of that cellular tower that was found via visible inspection weeks ago. (It would really help if I could draw a diagram... Maybe I'll work on that later)
The tech stated that to diagnose the issue, that tomorrow (12/18) he would come out early in the morning (6:30am) and install a tap/splitter on the cable that runs *to* the line amp, and hook me -- *just me, not my neighbours* -- up to that tap (this is apparently called a "ground line"), then monitor both my connection as well as my neighbour's. So in effect, I would have a direct line to the hub that connects to the node (i.e. no line amp for me), while my neighbours setup wouldn't change. This would be a temporary measure solely to try and narrow down which set of cable or piece of equipment is most likely the issue.
The theory is that if both myself and my neighbour continue to see the SNR issue, then it means the bad cable or bad piece of equipment is either at/around the tap I'm on, or further back from that (i.e. closer to the node). However, if only my neighbours see the SNR issue, then that means the bad cable/equipment is either the line amp or the stretch of cable that's between the line amp and where their connection comes in. (Sorry, this is really hard to describe without a visual diagram) We all agreed it'd be the best troubleshooting method for this, and scheduled to have it done between 0630 and 0830 the following morning.
So here comes the worst part of it all..
At 1930 that same night the tech came out and took readings/proposed the above, just out of no where, the SNR issue ceased. I changed nothing. My neighbour changed nothing. It just suddenly stopped for no reason. This has been one of the only times where things suddenly working actually made me furious!
The following morning the tech came out as promised and began the work proposed. I told him of the SNR issue ceasing the previous night and he was bummed out by that too, but regardless (understandably) went ahead with the proposed changes to the cabling to try and narrow this down. He padded the tap/splitter (so no need to install additional splitters at our cable box) and voilà, all done.
I also had him do another open input check with his analyser (I was wondering if the cellular tower had been shut off or simply stopped broadcasting) -- nope, still broadcasting nice and strong, i.e. 747/753MHz still have really high gain.
Anyway, my signal stats before:
Dec 17 14:56:00 Device Model: Motorola SB6121 (hardware version 5.0)
Dec 17 14:56:00 Firmware: SB_KOMODO-22.214.171.124-SCM01-NOSH (Aug 30 2012 15:35:46)
Dec 17 14:56:00 Boot Code: PSPU-Boot(25CLK) 126.96.36.199m3
Dec 17 14:56:00 Modem Uptime: 4 days 13h:10m:34s
Dec 17 14:56:00 Modem Status: Operational
Dec 17 14:56:00 Down Channel 1: 705000000 Hz, 0 dBmV power, 37 dB SNR, mod: QAM256, corr: 161369, uncorr: 733
Dec 17 14:56:00 Down Channel 5: 735000000 Hz, 0 dBmV power, 37 dB SNR, mod: QAM256, corr: 187313, uncorr: 590
Dec 17 14:56:00 Down Channel 6: 741000000 Hz, -1 dBmV power, 37 dB SNR, mod: QAM256, corr: 179164, uncorr: 479
Dec 17 14:56:00 Down Channel 7: 747000000 Hz, -1 dBmV power, 32 dB SNR, mod: QAM256, corr: 208803, uncorr: 560
Dec 17 14:56:00 Up Channel 8: 30600000 Hz, 46 dBmV power, 5.120 Msym/sec, status: Success
Dec 17 14:56:00 Up Channel 7: 35400000 Hz, 47 dBmV power, 2.560 Msym/sec, status: Success
Dec 17 14:56:00 Up Channel 9: 23700000 Hz, 46 dBmV power, 5.120 Msym/sec, status: Success
Signal stats after being given a "ground line":
Dec 19 19:02:00 Device Model: Motorola SB6121 (hardware version 5.0)
Dec 19 19:02:00 Firmware: SB_KOMODO-188.8.131.52-SCM01-NOSH (Aug 30 2012 15:35:46)
Dec 19 19:02:00 Boot Code: PSPU-Boot(25CLK) 184.108.40.206m3
Dec 19 19:02:00 Modem Uptime: 1 days 10h:25m:38s
Dec 19 19:02:00 Modem Status: Operational
Dec 19 19:02:00 Down Channel 2: 717000000 Hz, -1 dBmV power, 36 dB SNR, mod: QAM256, corr: 59185, uncorr: 635
Dec 19 19:02:00 Down Channel 3: 723000000 Hz, -1 dBmV power, 36 dB SNR, mod: QAM256, corr: 61702, uncorr: 635
Dec 19 19:02:00 Down Channel 6: 741000000 Hz, -1 dBmV power, 37 dB SNR, mod: QAM256, corr: 60489, uncorr: 722
Dec 19 19:02:00 Down Channel 8: 753000000 Hz, -2 dBmV power, 36 dB SNR, mod: QAM256, corr: 54379, uncorr: 634
Dec 19 19:02:00 Up Channel 8: 30600000 Hz, 38 dBmV power, 5.120 Msym/sec, status: Success
Dec 19 19:02:00 Up Channel 7: 35400000 Hz, 39 dBmV power, 2.560 Msym/sec, status: Success
Dec 19 19:02:00 Up Channel 9: 23700000 Hz, 37 dBmV power, 5.120 Msym/sec, status: Success
So now we simply wait for the SNR issue to happen again (to either myself and my neighbour, or just my neighbour).
I'll see if I can draw up a diagram of how all the cabling and stuff is run, just because it makes things a lot easier to understand.
As far as a root cause goes? The supervisor, tech, and myself are all in agreement -- the most likely candidate is something environmental, ex. a hair-line crack in some cable that gets stretched open when it's windy, a line amp that's allowing interference, or possibly a tap/splitter that's doing the same. We don't know which, but we're trying to narrow down the geographic location of which lines/cable/equipment it is.--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.