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Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

[Content] Channel Frequency Shift in Philly Region?

I'm just north of Philly in Lower Buck Co. We had a cable outage overnight between 9/17 and 9/18. I noticed yesterday that Comcast has shifted all the channels that were between 700 and 750 MHz down below 500 mHz except for the Music Choice stuff that remains at 753 MHz. They even shifted several of the 500 MHz channels lower in the bands.

Would this be due to the 700MHz+ interference issues that we've seen in my area ... probably due to cell interference. Or, would they be looking to expand the internet bandwidth which is currently running from 650-700 MHz.

My neighbors were already complaining about pixelation and drop-out on certain channels. Sure enough I checked my cable boxes and there seems to be a large downstream power drop (around 5 db) and SNR drop centered around 333 MHz. It's not affecting my service yet, but I could see how folks with already weak signals could run into problems with those channels.

What would be interfering around 333 MHz?

SeattleMatt
Streaming Tech Director
Premium Member
join:2001-12-28
Seattle, WA

SeattleMatt

Premium Member

[Content] Re: Channel Frequency Shift in Philly Region?

Brock-
Are you referring to HSI channels? Or QAM's for TV stations?

I know they had moved all of the HSI channels from the 700's into the 600's about at least a year ago.
Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

QAMs (256) for TV stations. Our HSI was shifted from the 700s to the 600s a couple years ago. When Comcast added new HD TV channels, they put them in the 700-750Mhz range. Those channels now have been moved to below 500 MHz as of yesterday.

The 327-333 MHz interference is also an issue with all the QAM TV stations using those bands.

andyross
MVM
join:2003-05-04
Aurora, IL

andyross to Brocktoon

MVM

to Brocktoon
Here by me in the Chicago area, most of the 700MHz channels were moved down, and some in the 500's were moved to the 200's. It also appears that some of the 700MHz are now used as a second bank of 8 channels for HSI (there appear to be 16 total now). I guess they assume modems can handle a bit of noise better due to error correction and TCP/IP retransmissions, versus annoying people with pixelation on their TV's.

telcodad
MVM
join:2011-09-16
Lincroft, NJ

1 edit

telcodad

MVM

said by andyross:

... I guess they assume modems can handle a bit of noise better due to error correction and TCP/IP retransmissions, versus annoying people with pixelation on their TV's.

Yes, that was my thought on this too.

While there is some error correction done with the Video QAM data stream, I'm not sure if it's the same and/or as strong/capable as that used for the HSI QAM data.

[ On the video STBs' Diagnostic "RF Statistics" screen (example: »Re: [Comcast Equip] Sound Dropping Out ), there are these three items:

- Corr Bytes: How many bytes were detected in error and corrected.

- Uncor Blks: How many data blocks that failed parity check, but could not be corrected.

- Errs Avg/Inst: Average and Instantaneous byte (or block?) Error Rate. ]
 
EDIT: Another, maybe more likely reason, could be the problem of 700MHz-band 4G LTE signals leaking directly into poorly shielded STBs: »Re: [Connection] Bad node / outside line again...
Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

Our HSI system is still 8 down and 3 up. As mentioned, maybe this is the 1st step towards 16 down?

Got home today and noticed the signal drop off around 333 MHz was gone, so maybe they're still working on the system.
rody_44
Premium Member
join:2004-02-20
Quakertown, PA

rody_44

Premium Member

Actually if you want to go back your area was in the 600s in the early 2000s. Than it went to 713 723 and now is back down in the 600s. They dont switch them around do to interference.

motorola870
join:2008-12-07
Arlington, TX

motorola870 to andyross

Member

to andyross
said by andyross:

Here by me in the Chicago area, most of the 700MHz channels were moved down, and some in the 500's were moved to the 200's. It also appears that some of the 700MHz are now used as a second bank of 8 channels for HSI (there appear to be 16 total now). I guess they assume modems can handle a bit of noise better due to error correction and TCP/IP retransmissions, versus annoying people with pixelation on their TV's.

I would assume so lol! TWC and Charter in North Texas use pretty close to the same QAMs for the DOCSIS channels in the 765MHz-813MHz range for DOCSIS carriers TWC uses 771MHz to 813MHz and Charter uses 765MHz to 807MHz. both sets of DOCSIS channels sit in the LTE bands.

owlyn
MVM
join:2004-06-05
Newtown, PA

owlyn to Brocktoon

MVM

to Brocktoon

Re: [Content] Channel Frequency Shift in Philly Region?

I checked some of mine a few weeks ago, and I noticed that there are now very few channels at the higher frequencies, and none at the highest. Used to be different, with several channels at the highest ranges. 750mhz plant.

motorola870
join:2008-12-07
Arlington, TX

motorola870

Member

hmm with as many people reporting that those QAMs are moving down to lower frequencies I can see 8 more DOCSIS channels going live soon. in the future I could see the 700MHz range used for DOCSIS 3.1 .
rody_44
Premium Member
join:2004-02-20
Quakertown, PA

rody_44

Premium Member

Im sure the 700 range is used for something. Internet doesnt have to rest at the top of the spectrum.

motorola870
join:2008-12-07
Arlington, TX

motorola870

Member

said by rody_44:

Im sure the 700 range is used for something. Internet doesnt have to rest at the top of the spectrum.

true but with Comcast emptying the 700MHz to 750MHz range out regionally it could signal a shift to 16 downstream bonding if the open QAM carriers are adjacent to the current 8 downstream bonded channels. just happens 705MHz to 747MHz is just enough downstream channels to make 16 downstream bonding a possibility.

Also the interference prone bands have been used in the past for DOCSIS channels I have seen some TWC systems use the FM band for the DOCSIS channels with mixed results on it working and they just moved those DOCSIS channels to the 600MHz and 700MHz area in North East Ohio to be able to bond 8 channels on the downstream. I have seen DOCSIS channels on 99MHz in some smaller cable company operations and it seems to work for them I also know that mediacom uses the lower 100MHz range for their DOCSIS channels in most markets in the midwest. I guess the FEC forward error correction in DOCSIS seems to be better enough to place DOCSIS channels in the LTE, Lower aeronautical bands, or FM bands than TV channels that would be tiling out if digital QAM carriers in a system that has problems with noise.
Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

Just an update for anyone curious ... looks like the TV ch. frequency shift was indeed to make way for 16 downstreams for internet.

Over the past month I was noticing 1 hour lease times on my IP address, usually signifying maintenance. It looks like overnight on Wednesday 3/11 they upgraded our CMTS as my modem was down for a bit and when it returned I had a new IP address and was bonding 16 channels .. the newer downstreams appear to have been added in the 700 + Mhz range.

Bad news is they need to either sweep the amps on the system or do some tuning at the CMTS. My upstream power has tanked to 29 - 33 db (from 36 - 40) and I'm seeing long bouts of T3 errors and packet loss. A tech is scheduled for this afternoon. Would this upstream power drop be due to a new CMTS? Possibly a line amp needs to be reconfigured due to the update? I'm sort of confused on how upgrading to 16 downstream channels dropped my upstream power levels so much?

None of the diagnostics / power levels changed on my DTA and DVR TV boxes. This only is affecting the CMTS / modem signals right after the update ... killing my service.

caster
@sysvana.com

caster

Anon

what about TV will that be used in 750-1000 any more or the will they cut more HD to fit it in to the lower area.
Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

At least in my area, they're not running anything above 753 MHz. I think the internet downstream runs up to near 750, and then at 753 MHz Comcast has a bunch of 64 QAM music choice channels.

Comcast has started adding more HD channels per frequency, so that's probably how they'll continue to add HD in the lower frequency ranges. Don't know how bad the pic quality will get hit though.

telcodad
MVM
join:2011-09-16
Lincroft, NJ

telcodad to Brocktoon

MVM

to Brocktoon
said by Brocktoon:

Bad news is they need to either sweep the amps on the system or do some tuning at the CMTS. My upstream power has tanked to 29 - 33 db (from 36 - 40) and I'm seeing long bouts of T3 errors and packet loss. A tech is scheduled for this afternoon.

Would this upstream power drop be due to a new CMTS? Possibly a line amp needs to be reconfigured due to the update? I'm sort of confused on how upgrading to 16 downstream channels dropped my upstream power levels so much?

None of the diagnostics / power levels changed on my DTA and DVR TV boxes. This only is affecting the CMTS / modem signals right after the update ... killing my service.

Yeah, that upstream power is very low, which is probably allowing ingress noise to become a significant problem on the upstream, causing a low uSNR and those T3 timeouts:

From: »Comcast High Speed Internet FAQ »What do messages about timeouts mean?
quote:
T3 ( Ranging Request Retries Exhausted )

Explanation: The cable modem has sent 16 Ranging Request (RNG-REQ) messages without receiving a Ranging Response (RNG-RSP) message in reply from the CMTS. The cable modem is therefore resetting its cable interface and restarting the registration process. This typically is caused by noise on the upstream that causes the loss of MAC-layer messages. Noise could also lower the signal-to-noise ratio (SNR) on the upstream to a point where the cable modem's power level is insufficient to transmit any messages. If the cable modem cannot raise its upstream transmit power level to a level that allows successful communication within the maximum timeout period, it resets its cable interface and restarts the registration process. This error message is DOCSIS event message is R03.0, Ranging Request.
I don't think changing the CMTS would cause this, most likely a change at the node or some line amps.

They may need to adjust your line tap if your downstream power levels are running hot also.
Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

said by telcodad:

I don't think changing the CMTS would cause this, most likely a change at the node or some line amps.

They may need to adjust your line tap if your downstream power levels are running hot also.

That's where I'm confused and find things a bit odd. Before the upgrade to 16 channels overnight, when it was 50F outside, my downstreams were ~ +5 db, and my upstream were ~ 37-40 db. Right after the upgrade at 50F my downstreams are ~ +1 db and upstream 29 - 32. I figured if the upstream dropped, I would have saw a rise in the downstream power ... but both dropped. While I checked the signal levels from various TV frequencies on my DTA and there was no change at all on those power levels. This seems to only be affecting the internet frequencies.

I guess this is a better discussion for the HSI board, but why would just switching to a new IP and 16 downstreams change my upstream power level so much? This happened immediately after the late night switchover. I'm concerned that if the tech messes with the tap it will lower my downstream on my TV boxes which already run lower downstream than the modem. Fix the internet, and now my TV doesn't work ...

telcodad
MVM
join:2011-09-16
Lincroft, NJ

telcodad

MVM

said by Brocktoon:

said by telcodad:

I don't think changing the CMTS would cause this, most likely a change at the node or some line amps.

They may need to adjust your line tap if your downstream power levels are running hot also.

Before the upgrade to 16 channels overnight, when it was 50F outside, my downstreams were ~ +5 db, and my upstream were ~ 37-40 db. Right after the upgrade at 50F my downstreams are ~ +1 db and upstream 29 - 32.
:
I'm concerned that if the tech messes with the tap it will lower my downstream on my TV boxes which already run lower downstream than the modem. Fix the internet, and now my TV doesn't work ...

Yes, moving to a higher tap value then would reduce your downstream power below the optimum 0 dBmV mid-range value.

Looks like Comcast needs to adjust a return-path amp to increase your upstream signal levels closer to 40 dBmV.