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Signal levels and setup question, also QAM vs OFDM

Hwaiting
I plan to stick around

Hi all,

TL;DR - my OFDM levels and correctable codewords seem high. Would removing the amp + splitter put the OFDM levels more in range even if it may cause QAM levels to suffer?

 

The cable that enters my home through the electrical box in the basement is connected to amplifier (Antronix MVRA501B). The amp was installed by Rogers during my pre-Ignite days where I had 4 cable runs throughout the home. When I switched to Ignite, the install tech didn't check any part of that so the amp is still part of the setup. I ended up disconnecting 3 of 4 lines from the amp and put terminal caps on the unused outputs on the amp.

The one active cable from the amp goes up to the 2nd floor where the XB7 is. As the signal was too strong the tech installed a splitter (-3dB) before the modem.

I've always had that QAM high frequency roll-off so I thought I needed the amp but I see my OFDM levels seem high. I also see that I have a high number of Correctable Codewords for my OFDM channels. Is this a problem?

I think I read somewhere if you have OFDM, then it's more important to keep those happy vs the QAM channels. Is the range for OFDM like QAM (+-10dBmV and around 38dB)?

Should I remove the amp & -3dB splitter and would that improve my situation? I don't have any critical issues aside from only getting 80% of advertised speeds (400Mbps on a 500Mbps plan). If I remove the amp, I think it may cause some of the high freq QAM channels to go beyond -10dBs so I'm not sure if I should. Back when I had the CODA, I was getting similar if not slightly higher speeds on a 300Mbps plan).

Any advice would be appreciated. Thanks.

 

Downstream

Channel Bonding Value                                  
Index

13

1

2

3

4

5

6

7

8

9

10

11

12

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

34

33

34

Lock Status

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Locked

Frequency

651 MHz

279 MHz

579 MHz

585 MHz

591 MHz

597 MHz

603 MHz

609 MHz

615 MHz

621 MHz

633 MHz

639 MHz

645 MHz

657 MHz

663 MHz

669 MHz

675 MHz

681 MHz

687 MHz

693 MHz

699 MHz

705 MHz

711 MHz

717 MHz

723 MHz

825 MHz

831 MHz

837 MHz

843 MHz

849 MHz

855 MHz

861 MHz

216 MHz

350000000

216000000

SNR

37.6 dB

39.2 dB

40.6 dB

40.6 dB

39.8 dB

39.6 dB

39.8 dB

39.1 dB

38.4 dB

38.8 dB

38.6 dB

38.7 dB

38.3 dB

38.0 dB

38.1 dB

37.8 dB

36.6 dB

38.0 dB

37.4 dB

37.2 dB

36.8 dB

36.1 dB

35.9 dB

35.9 dB

36.4 dB

36.5 dB

36.6 dB

36.7 dB

36.8 dB

37.2 dB

37.3 dB

37.4 dB

42.8 dB

40.9 dB

42.7 dB

Power Level

-3.0 dBmV

4.4 dBmV

1.5 dBmV

1.3 dBmV

1.3 dBmV

1.1 dBmV

0.5 dBmV

0.1 dBmV

0.7 dBmV

0.8 dBmV

-1.5 dBmV

-1.8 dBmV

-2.3 dBmV

-3.0 dBmV

-3.1 dBmV

-3.1 dBmV

-3.1 dBmV

-3.3 dBmV

-3.8 dBmV

-4.4 dBmV

-5.0 dBmV

-5.7 dBmV

-6.1 dBmV

-6.1 dBmV

-5.4 dBmV

-5.1 dBmV

-5.1 dBmV

-5.0 dBmV

-4.6 dBmV

-4.6 dBmV

-4.4 dBmV

-4.5 dBmV

9.3 dBmV

5.5 dBmV

9.2 dBmV

Modulation

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

256 QAM

OFDM

OFDM

OFDM

 

Upstream

Channel Bonding Value 
Index

1

2

3

4

Lock Status

Locked

Locked

Locked

Locked

Frequency

21 MHz

25 MHz

32 MHz

38 MHz

Symbol Rate

2560

5120

5120

5120

Power Level

36.8 dBmV

39.0 dBmV

41.0 dBmV

41.0 dBmV

Modulation

QAM

QAM

QAM

QAM

Channel Type

TDMA_AND_ATDMA

ATDMA

ATDMA

ATDMA

 

CM Error Codewords

                                 
Index

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

Unerrored Codewords

3427353530

4276686330

4276698476

4276725936

4276755056

4276770164

4276783570

4276810139

4276820842

4276825259

4276845268

4276849272

4276852299

4276854167

4276865294

4276869339

4276882412

4276898483

4276907401

4276913074

4276929965

4276936737

4230822981

4276952588

4276956256

4276961790

4276974188

4276974622

4276989424

4276991390

4276996022

4276994728

2737725724

3427353530

Correctable Codewords

251038570

0

3

0

1

2

0

0

2

0

0

1

3

4

2

5

4

10

13

43

110

296

599

653

360

235

177

164

93

79

42

43

2330990283

251038570

Uncorrectable Codewords

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

92

237

0

0

0

0

0

0

0

0

1

0

 

1 REPLY 1

Re: Signal levels and setup question, also QAM vs OFDM

-G-
Resident Expert
Resident Expert

@Hwaiting wrote:

Hi all,

TL;DR - my OFDM levels and correctable codewords seem high. Would removing the amp + splitter put the OFDM levels more in range even if it may cause QAM levels to suffer?


Having a high number of correctable errors on an OFDM channel is not a problem.  It's actually a good thing.  (See this topic for more info.)  The important thing is that you have zero (or close to zero) uncorrectable errors.

 

The cable that enters my home through the electrical box in the basement is connected to amplifier (Antronix MVRA501B). The amp was installed by Rogers during my pre-Ignite days where I had 4 cable runs throughout the home. When I switched to Ignite, the install tech didn't check any part of that so the amp is still part of the setup. I ended up disconnecting 3 of 4 lines from the amp and put terminal caps on the unused outputs on the amp.


I would remove the amp.  It's probably a "zero gain" amp (0 dB gain on the output) and these are typically used where the signal coming into the home is good but a passive splitter would cause the output to drop to unacceptable levels.  With a "zero gain" amplifier/splitter, the output signal should be at the same level as the input signal... so there is no benefit to leaving it installed if you only have one coax-connected device in your home.  Also, while the signal will not get boosted, noise will... and that is not good.

 

Remove the amplifier/splitter and use an F81 barrel connect to connect the incoming coax feed to the coax line leading to your gateway.  Alternatively, you can use the splitter that the tech installed as well.

 

I'm not sure what to make of your signals.  Your OFDM channels are reading 9 dBmV but you have other QAM channels reading -6 dBmV.  Will be interesting to see if things level out after removing the amplifier.

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