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Old 12-07-2012, 02:39 AM
Xymox Xymox is offline
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Default Modifying a DPC3010 for performance

A month ago I decided to get a new modem as Cox was about to offer 100Mb/s down and 10Mb/s up. I wanted a 8x4 as i only had a 4x4. This led me down a interesting road. I wanted to see what was the best performance modem. I got a SB6180 and a DPC3010. I was shocked that internally they were almost identical right down to part numbers on the board. Layout was different tho. This might effect RF performance. However after ALOT of testing these modems perform indentically except for the GUI. But im sure you guys know this.

I decided on the DPC3010 because Cox has more frequent firmware updates and better hardware support for it. The CMTS is after all a Cisco.

Im a EE and I constantly improve any device I use. Right off a large number of things in the design stood out as needing improvement. In fact there were a number of spots on the PCB in the power supply that were not populated with parts. This was a obvious cost saving step and they did just enough in parts to squeak by Cable Labs certification. It was clear a lot could be done to improve the hardware.

A Cable Modem is a very analog device. QAM is a highly complex and fairly finicky system. The cable modem transmits a complex signal that must be incredibly timed and very precise. While it has systems for error correction these error corrections cause some cpu time and produce jitter. Uncorrectable errors produce a retransmission and a larger jitter component. How good the sync is with the CMTS also effects jitter.

Jitter is a issue that effects some key things. Like gaming or to some degree VoiP. Obviously less correctable errors the better. There are other measures of a connection I wont bore you with here but all are effected by the analog performance of the cable modem.

Right away the power rails of the CM were obviously hurt by cost reductions in manufacturing. I stuffed a huge number of huge solid tantalum caps across these rails, in each switching power supply for each of the 3 power rails, put them at the points on the BCM3380 where power enters the chip and also addressed the special power rail that supplies the LNA chip in the RF section. Overall it was a hugh amount of tantalum. I think I dropped in twice the cost of the whole modem just in tantalum caps. I also used some big electrolytics to provide the big guns to quiten the supplies all the way down. I used tantalum for a number of reasons but low ESR at high frequencies is the most important here.

The overall effect on the power rails was dramatic. Measured at the chip power entry pins a 1,000:1 reduction of noise occurred. Also the chip now had very stable power rails to create the upstream signal and very very quite rails to listen to the downstream QAM.

The performance effect was interesting. A 1db increase in downstream levels occurred along with a full 1db increase in S/N. The upstream power decreased by 1.5db indicating that the transmitted signal was being seen more clearly now. My correctable errors dropped by half. My buddy at Cox told me all my performance numbers had a dramatic increase in performance.

My levels ended up at +6-7 downstream and 38.5 up with a 41.1 db S/N in a 8x4 config.

I purchased 2 DPC3010's. I kept one unmodded to compare.

I used Multiping set to do 10 pings a second and chart it. My target was the CMTS IP. I did weeks of charting and then did mods and did more charting. The differences were quite interesting.

The large jitter was reduced very obviously. A much smoother and consistent connection resulted.



I have the Ultimate Tier of service from Cox and in my area its capped currently at D 65 U 5.5. The mods did not change this but testing did become VERY consistent.

Of course other things improved. The stability of the modem was seriously improved as the supplies were now noise free and the regulation was very consistent. Impulse current draw by the CPU is easily fed from the caps. I expect one of the big performance improvements is long term reliability.

Speaking of reliability...

The thermal management of both the SB6180 and DPC3010 is PISS POOR. These things are way overheated. While it might not be a problem initially over time the high heat will degrade performance and eventually kill the modem. The heat sink was crap. I replaced it with a much better heat sink, using Artic Silver heat sink compound and added a Silenx fan. I also modded the case to allow far more air thru the case. I power the fan off the 12V power coming into the unit.

Speaking of the power supply. Because of the higher inrush current caused by the startup of all the new caps a larger power supply was needed. I settled on a 3A 12 supply. This is overkill but the .4 Adc nominal that the modem draws wont even heat up the 3.5 amp supply again providing long term reliability improvements as the power supply is not gonna burn out any time soon.

A also added a TII gas based surge suppressor in the coax right before the modem to protect it from the outside world. http://tiinetworktechnologies.com/re...DS036-0710.pdf

The caps used were:
The yellow ones are 100uF 16V kemet Tantalum
The black caps to the left of the heat sink are 1000uF 16 v and 2 are stacked per rail.
I used a 560uF wet tantalum - its the silver one. Its highly expensive and I used it as I had it lying around. You dont really need it.
There is a big 3300uF 16V electrolytic on the right of the heatsink.

Some pics...





A bit fugly, but functional.




It was a fun project and I think I have the best DOCSIS 3 modem on earth ! hahaha...

The improvements are noticable using the web. I think gaming would be better as there is less jitter. It would be more responsive. For normal web browsing it might seem a bit more response and quicker.

I have a fairly fast home networking setup. Im using a older gaming machine running Vyatta which turns it into a Linux based high power router. I am also running a high performance rDNS caching server on it with settings for performance and carefully chosen DNS peers based on performance. All my wiring is cat 7a shielded.

My electronic test equipment list is extensive and I did lots of measurements as I went in the mods. I have everything from a 1Ghz spectrum analyzer to great scopes, rubidium based freq counter and great DMMs.

I figured you guys are already doing tweaks to cable modems so this might be a fun project. I posted here as you guys understand that the problem is, just like other endevors on this site, modifying a cable modem is a no no...

Have fun !

Last edited by Xymox; 12-07-2012 at 03:08 AM.
  #2  
Old 12-07-2012, 02:57 AM
Xymox Xymox is offline
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I am in need of a bcm3380 data sheet. If you might have one, i sure would appreciate it

Also does anyone know if the calibration settings stored someplace in NVRam can be edited and modified ? Specifically I need to be able to replace the clock crystal with a far more stable one but to do so I have to change the calibration settings to trim the new crystal to the exact 48.00000000 required. There must be a whole set of calibration settings and procedures and I would sure like to be able to do myself.


Last edited by Xymox; 12-07-2012 at 03:06 AM.
  #3  
Old 12-07-2012, 05:47 AM
justsomeguy justsomeguy is offline
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very nice work,

thanks for sharing !!
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  #4  
Old 12-07-2012, 08:15 AM
usbbdm usbbdm is offline
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Great work. I think none of us had done mods close to that.
Anyone have the datasheet for Xymox? I know Broadcom's datasheet is hard to get. However, there still should be someone owns it. You can contact Xymox private.
  #5  
Old 12-07-2012, 03:47 PM
Xymox Xymox is offline
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Yes I would do more if I had a datasheet.

If staying anonymous is important in sharing a datasheet im sure there must be some way to get the file completely anonymously.

What would be really good right now tho is if anyone knows any thing about the calibration of the bcm3380. There must be a few NVRam bytes that control trimming the clock freq. I could really use those and some way to change them. I would imagine that Broadcom has a program for doing calibration and oh-man would I love to get hold of that program. Being able to carefully hand calibrate a modem would be very cool indeed.
  #6  
Old 02-11-2013, 09:25 PM
Xymox Xymox is offline
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Just a update after Cox switched on hyper high speeds here in phoenix..

The modem has now gone flawlessly for 3 months. Perfect operation..

  #7  
Old 02-11-2013, 09:57 PM
Tropical
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no point of doing this.
  #8  
Old 02-12-2013, 05:19 AM
justsomeguy justsomeguy is offline
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Quote:
Originally Posted by Tropical View Post
no point of doing this.
it is done because it looks like the guy doing it wanted a cool project for the weekend!..there are many things that do not need to be done, but what's the fun in not doing them? living outside the box a bit is very usefull in all aspects of life.

throwing negativity around is NOT usefull..please dont start up again..remember that comment when you were little...if you can't say nothing nice dont say nothing at all ? i think that really applies to YOU...please refrain from posting cinical comments and only post if your actually going to help someone, or have something that is actually productive to say..
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  #9  
Old 02-12-2013, 06:01 AM
syankey1970 syankey1970 is offline
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Quote:
Originally Posted by Tropical View Post
no point of doing this.
Are you kidding me? Did you actually READ his post? That's one of the coolest things I've seen in this hobby in a long time. He took a subpar product and modified it to be what it should have been before it was released. Obviously, according to the the cost of the mods he made, it would never be produced that way as no one would pay three times the current cost of a 3010.

Absolutely fantastic post! I really appreciate someone who goes to such lengths to make something better than it was originally. He should post that on SBH as well...
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