@BS, you ask a couple of questions in a blog a couple of weeks ago and I haven't managed to get back to it. Sorry for the delay. From the sounds of it, you're not having much fun with your wifi service, for various reasons.
First a question. You asked about any issues caused by splitting the cable service for cable tv and internet. The splitter will cause a 3 db drop for each outbound port. If you have enough signal excess, this shouldn't be an issue. But, if your signal levels are marginal, then yes, 3 dB could make a difference. It all depends on where your current signal levels are. If you have a look at the DOCSIS WAN tab in the modem, that will very quickly let you know where you stand. Ideally, the downstream DOCSIS 3.0 levels should be around 0 dBmV with a signal to noise ratio of 36 to 40 dB. The upstream DOCSIS 3.0 levels, if one OFDM downstream channel is showing active will be in the 30 to 32/33 dBmV range.
Now, if you happen to have a cable port upstairs that is centrally located, you could install an F-81 connector downstairs to join the external cable with the single upstairs cable, and then install the splitter at the upstairs cable port to run both cable tv and internet modem from that port. It all depends of course on what that might do to any fixed ethernet cabling. F-81 connector looks like the following:
https://www.lowes.ca/coax-cable/ideal-3-ghz-f-splice-adapter-4-pack_g1200823.html?SearchTerm=85-339
Or, if you can manage to snake a cable upstairs so that you can relocate the modem upstairs, that might do the job as well. For wifi purposes, bringing the modem closer to the devices results in a couple of improvements, the received signal level increases as does the signal to noise ratio. If you look at the following Modulation and Coding charts, that pushes the data rates down the chart.
https://www.wlanpros.com/mcs-index-charts/
Consider each spatial stream to equal one antenna in the router. You start at the top, with 1 out of every two data bits being used for data purposes. The other bit is for error correction. Down at the bottom of the single stream group (top group), you end up with 64 QAM and 5 out of 6 bits being used for data and only 1 bit being used for error correction. The end result can be very dramatic depending on where you're starting from. If you can manage to run anything with 5 Ghz 80 Mhz (bandwidth) channels, that will also make a considerable improvement.
This doesn't solve the issue of sharing channels with the neighbours, but, it should make a considerable difference in data rates despite that channel sharing.
When you have time, can you have a read thru the following post from tonight, specifically looking at the wifi settings and the wifi scanners.
https://communityforums.rogers.com/t5/Internet/slow-wifi/m-p/437127#M55494
Just to note, TKIP can/will cause slower data rates. From what I remember its not officially compatible with the 802.11n spec. Understanding that you have some older devices running, that might be something to think about, slow data rates to support older devices versus retiring those devices.
Something to think about is the use of the Dynamic Frequency Selection channels, which lie between the lower and higher end of the 5 Ghz band. Those channels are shared with Weather Radar and there are requirements for the modem to monitor its active DFS channel for any Weather Radar transmissions. If that transmission is encountered, then the modem has to evacuate that channel and go elsewhere. Here's a link to yet another post, this one covering the DFS channels.
Now, if you can manage to use those channels without any interference from Weather Radar, that might solve part of the problem of competing with the neighbours. The drawback to these channels is the possibility of some devices not supporting the 5 Ghz DFS channels. The device would appear to connect to the channel, but, it simply won't go anywhere. You would know in a minute or two if any device is old enough or not designed to allow DFS use. Just for curiosity's sake, I'd give that a go. Have a look with inSSIDer Lite to determine if anyone nearby is using any of the DFS channels. Hopefully not, then kick the 5 Ghz wifi channel into the DFS range.
To do that, log into the modem, navigate to WIRELESS .... ADVANCED and enable the DFS channels. Reboot the modem, ADMIN .... DEVICE RESET .... Reboot.
After the reboot, log back into the modem and navigate to the WIRELESS .... BASIC SETTINGS and select one of the DFS channel groupings. I think there are three to choose from. You would have to monitor that wifi connection to see if its stable or if it changes channel due to any detected Weather Radar transmissions.
So, food for thought, if you still have the 4582, and if you can manage to relocate it upstairs, you might get your money's worth out of it.
Other food for thought, if you have a house with a main floor, and just the basement, you could consider a router that has external antenna. That antenna can be replaced with higher gain antenna that limits the vertical power distribution and increases the horizontal power distribution. Understanding the issue of budgets, with after christmas sales going on, it might be possible to pick up a router at a good price that would allow you to swap the antenna. Just have to be careful to buy antenna that runs both 2.4 and 5 Ghz.
