Bad signal - but only when hot?

I've noticed that our modem signal changes dramatically when we are in the heat of the day here in Texas. It's the same pattern each day.


Right now it's evening, the best channel has -4.0 dBmV/39.3 dB power/SNR and the worst channel has a -12.0 dBmV/33.1 dB power/SNR. In the afternoon when the temperature outside is up near 100F then the worst channel is at <15 dbmV and <30 SNR - and we see a lot of errors on the channels with lowest signal. Today we also had many more issues with internet and some TV channels around 5pm, but things became watchable again as it got cooler in the evening.


The house is a year old with RG6 cabling. The TWC installation was last week with a single 3-way spliter feeding our modem, the telephone adapter and the cable box. The installers removed the splitter in our attic leading to other room, so the feed into the house goes directly to the single 3-way spliiter.


Just wondering if it's usual to see poor signal when it's getting very hot - and also such a big difference in power between the best and worst channel on the modem?


I tried to raise the issue with a TWC chat agent - but they were only interested in if things were working now, which they are - as it's now the evening and cooler.


The current modem stats, from the cooler evening, are below.




Downstream Bonded Channels Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables

1 QAM256 783000000 Hz-4.0 dBmV39.3 dB502131649802
2 QAM256 771000000 Hz-4.1 dBmV39.0 dB408489620542
3 QAM256 777000000 Hz-4.0 dBmV39.2 dB415301626134
4 QAM256 789000000 Hz-4.3 dBmV39.1 dB419205614580
5 QAM256 795000000 Hz-4.7 dBmV38.9 dB414549600527
6 QAM256 801000000 Hz-5.8 dBmV38.4 dB419958611905
7 QAM256 807000000 Hz-7.4 dBmV37.6 dB415227614369
8 QAM256 813000000 Hz-8.9 dBmV36.8 dB342736476458
9 QAM256 819000000 Hz-9.8 dBmV36.1 dB378886551866
10 QAM256 825000000 Hz-9.8 dBmV36.0 dB420235640514
11 QAM256 831000000 Hz-8.6 dBmV36.7 dB423710626246
12 QAM256 837000000 Hz-7.8 dBmV37.1 dB427504632512
13 QAM256 843000000 Hz-8.8 dBmV35.9 dB439395633777
14 QAM256 849000000 Hz-9.2 dBmV35.9 dB445906608054
15 QAM256 855000000 Hz-10.4 dBmV34.9 dB482633653871
16 QAM256 861000000 Hz-12.0 dBmV33.1 dB513365811145120


Total Correctables Total Uncorrectables



Upstream Bonded Channels Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power

1 ATDMA 5120 Ksym/sec30600000 Hz51.0 dBmV
2 TDMA 2560 Ksym/sec19400000 Hz49.0 dBmV
3 ATDMA 5120 Ksym/sec24200000 Hz50.5 dBmV
4 ATDMA 2560 Ksym/sec37000000 Hz52.2 dBmV




Re: Bad signal - but only when hot?

Yes, the signal will drop with temperature, this is normal, and if your line, and equipment are in order,

you would never notice the problem since it would stay in range, your signals are high on the upstream

and low on the downstream.walk or look at  your cable make sure everything is tight/firm, no wrench,

tech will need to come back as you have a cut in your line, bad connection.


Re: Bad signal - but only when hot?

Your entire connection is out of spec, There are too many or open port splitters and probably trashed coax outdoors from weather or rodents/ raptors or worst yet, rg 59.

Your modem & dvr's won't work right

modem must be on no or the first 2 way splitter, check your wiring!



Re: Bad signal - but only when hot?

I've gone through looking at all the cable. In the house it's all RG6 only 12 months old with no damage I can see. All connections are tight and there are definitely no open ports or extra splitters in the path. The splits to other rooms were disconnected by the installers, with a straight coupler from drop coming in to only room with equipment. The drop from pole to house is new as of last week.

The 3 way splitter was put in by the TWC installers and the modem is on the -3.5db output, which I believe is same as having it on first 2 way.

Any hints on getting a tech out? The chat support claimed to have looked at the modem/tv signal from their end and said it was pretty good.... I pasted the same modem signal to them as I showed here.


Re: Bad signal - but only when hot?

those levels are terrible... Move the modem to where a dvr is and see what the levels are.

I don't understand how lines can be new and already spliced because there were too many splitters...


Is this overhead line? Does it run thru trees? Can you get a photo of the pole connections, looking for any additional splitters for neighbors?

If you have a neighbor on the same tap, see what there levels are.


Look in the dvr's diag page and see if those are 3.5 db worst to verify the ports are as you stated.

 Hold in the select for 10 seconds and then hit the up arrow...


 TWC needs to send a tech out



Re: Bad signal - but only when hot?

They are now sending a tech out tomorrow after directed an agent at this forum thread. Thanks - seems like a good way to avoid runaround.


I'd already tried moving things on the splitter, and the modem signal does how about 3db lower if moved to the DVR port on the spliiter - so the 1 port at -3.5dB, 2 ports at -7dB seems accurate.


We previously had Verzion FiOS for a year. That had a single 2-way 5-1000MHz splitter in the attic to feed 2 rooms only - single DVR and FiOS MoCA router in separate rooms. The cabling was put in by builder and verizon connected and put in that single splitter. At TWC install they replaced the 2-way in the attic with a straight through coupling between feed coming from drop and outlet in one room only - where there's our 3-way splitter and all connected equipment. So we have


pole----->TWC box on house----->attic-straight-coupler----->outlet----->3-way splitter (modem/DVR/telephone adapter)


The line is overhead from pole (which is at end of our driveway) to house and completely clear of trees. Not at home for a photo now - but from looking at pole previously our drop seems to come out of a 6-port tap which is right next to what I believe is a amplifier (grey box with fins attached to larger cables running down street). Nobody else is connected and no neighbors to check with. Everyone is FiOS - as we were before Frontier purchase gave loads of issues and we decided to switch to get more for less.


Thanks again!


Re: Bad signal - but only when hot?

All that's in the TWC box is a grounding block, not a splitter, correct?

 normal tapoffs are 2-4-8's

Sounds like there's an issue up there and it's either blown or the wrong value

 Look at your DVR levels and see if they're 3 dB worst

If so, it will be unreliable as well.




Re: Bad signal - but only when hot?

Looks like something major now. Just got home and no internet, no tv channels or phone at all. Modem can't find any channels.

Hopefully they fix tomorrow it tomorrow. At least now it's obvious there's a problem :-)

Re: Bad signal - but only when hot?

Print out that last level page for the tech, Tell him it gets 4 dB worst at times, It's now out of spec out of range.



Re: Bad signal - but only when hot?

Too much to hope for.... things came back from the total outage with just the same bad signal. TV reception is bad and modem low power etc.


Looks like our drop comes from an 8-way tap at the pole. The TWC box on house only has one cable in and one out - so presumable just a ground block, no splitter.


Fingers crossed it gets fixed tomorrow.



 Picture of pole + drop