Modifying a DOCSIS 3.0 cable modem for high performance
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If he really wanted to improve the RF performance of his modem, he should have used small, low-value, surface-mount capacitors instead of the large tantalum capacitors with relatively long leads and large electrolytic capacitors. Cable modems and other RF equipment operate at very high frequencies by definition, and tantalum & electrolytic capacitors with long leads are ineffective at these high frequencies. The long leads of the capacitors act as inductors, which will prevent the high frequency fluctuations from ever even reaching the capacitor.
If you look closely, you can see that he added his tantalum capacitors to the already-present small ceramic decoupling capacitors. If he really wanted to improve the RF performance of the circuit, he would have been better off adding more low-value, surface-mount ceramic capacitors in parallel with the pre-existing ones to help with the high-frequency decoupling, where it counts in an RF circuit. If he was really adventurous, he could splice some ferrite beads in series with the supply lines to form an LC filter for even better noise rejection.
Furthermore, he could have taken measures to improve the S/N ratio of the circuit by improving the shielding around the sensitive RF circuits in the middle of the board. You can see where the designer originally made room for a shield "can" to be soldered over the sensitive components, indicated by the exposed copper rectangle around the heatsink area. However, you may get unlucky if your shield can volume has resonant frequencies in the operating range of the circuit which will trigger feedback and render the circuit inoperable. A safer option would be to add some RF-absorbing foam over the sensitive area to absorb the noise.
It's not like he did a google.com ping on each and called it a day... From the post:
> 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.
Weeks of charting should more than correct for other factors.
By reducing power noise in that area (including noise created by the consumption variation due to the processor/circuitry itself) you end up reducing some noise in the RF section as well
A cable modem's upstream power level has nothing to do with noise. The CMTS will always power adjust the modem so that it hits the CMTS at 0db, it doesn't power adjust based on noise. A 1.5 db change in Upstream SNR would be a different story, but that is a reading that can only be obtained from the CMTS so there isn't any data to backup that claim.
I also would dispute the clam that a modem vendor or MSO is trying to only minimize the cost of the cable modem. If minor internal changes reduced the number of service calls and truck rolls a small increase in upfront cost would quickly be recovered.
Also, he reduced the noise on the DC part of the circuit, from looking the pictures posted it doesn't look like he touched the RF part at all.
So it kinda looks like racing stripes on a Geo to me. The claimed improvements could be due to almost anything including unplugging the coax and plugging it back in differently, atmospheric conditions, time of day, etc.
It was the same with PC monitors, for years LCD models had ENORMOUS input lag and crappy features, but now we see models with 120HZ and no input lag/passtrough mode appearing.
http://webcache.googleusercontent.com/search?q=cache:iqkzgJs...
Google "high upstream power level" and there are bazillions of people suffering from this problem with all kinds of different solutions.
I'm in VA now with Cox instead of Charter, but dealing with a very similar modem and now, very similar problems. I'm gonna order another one (fairly cheap online) and see if I can do some of these modifications to improve performance and upstream power levels.
That or i'll cave-in and switch to Fios.
Low-inductance decoupling across every chip supply is the extremely important part, and for that you really want ceramic surface mount caps either replacing or stacked on top of existing ones. I'd recommend skipping tantalum caps altogether and filling that size/freq tier with larger ceramic multilayers since you're not designing for cost.
And of course low-esr electrolytics on the rails to reduce power supply ripple and all that. And some ceramic decoupling caps on both sides of switching regulators too. But definitely make sure the output of every voltage regulator (switching and linear) remains stable and hasn't started oscillating.
On the other hand, maybe it's only cheap because Comcast doesn't support it?
I've noticed that Time Warner rents really cheap modems but for BYO they only support the most expensive models. I don't know why that is (one might speculate that they want to keep you renting since it's more profitable for them).
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I've spent many hours in the past with Internode tech support trying to resolve some of my connection's issues to no avail. It does some really funky stuff too when I play with the settings, so I'm sure there's room to improve but I can't do it with just software.
That's not record-setting of course, but it more than covers the ISP speed offerings I'm aware of. Aside from fiber, which is not pre-laid for most last-mile applications, what would be faster?
DOCSIS 3.1 brings OFDM as well as up to 10 DL /1 UL Gbps. At that sort of speed, as well other added reliability features finally makes Cable a decent Alternative. Speaking from experience in EU and Asia Area. No idea if it is the same in US.
Everybody here thinks it's a joke, unfortunately it's not. http://abbottsinternet.com.au/
For this I currently pay about $75 per month. Sigh.
The government needs to re-negotiate it's deal with Telstra, and I expect the HFC network remaining with Telstra as a wholesaler monopoly will be a part of that.
No-one has said they're going to "rip up" the HFC cable. It was to be decommissioned under the old NBN plan and it's future hasn't been decided under the new.