[mythtv-users] Pixelation/Bad Recordings HDHR Prime -- I am at my wits end

Thu Aug 29 16:12:12 UTC 2013

On Thu, Aug 29, 2013 at 7:56 AM, Captain Hook <captainhookzero at gmail.com>wrote:

>
>
>
> On Wed, Aug 28, 2013 at 3:35 PM, Greg Woods <greg at gregandeva.net> wrote:
>
>> On Wed, 2013-08-28 at 12:09 -0700, Gary Buhrmaster wrote:
>>
>> > With rare exceptions, the "management" address for all cable modems
>> > is 192.168.100.1
>>
>> Certainly not so any more. I just got a new modem from Comcast, a DOCSIS
>> 3 to replace the old DOCSIS 2. This modem is clearly designed as a "one
>> size fits all" for all of their customers. It has jacks for the phone
>> service. It has a wireless access point built in and four ethernet
>> ports. It is hard-coded with an IP address of 10.0.0.1, and it insists
>> on assigning 10.0.0/24 addresses to every machine in the house. The old
>> dumb modem was really just a bridge; whatever machine you plugged in to
>> the ethernet port got the public IP.
>>
>> For me, this change sucked, because I have IP addresses hard-coded in
>> all sorts of places (including MythTV of course). So I basically had to
>> reprogram my Linux system that was acting as my router to account for
>> this; it is attached to the "house" network, so that all the other
>> machines in the house can keep their IPs. And then it is attached to the
>> 10.0.0/24 net and sets its default route to 10.0.0.1. Thus I have
>> another router between me and my public IP. I had to make a number of
>> other changes to make this work (IPSEC tunnels and so forth; fortunately
>> the Comcast box at least supports port forwarding). I continue to use my
>> Netgear router as the wireless base station (that's all the Netgear is
>> now, but it can be put into place to replace the Linux router if there
>> should be problems with that box). The Comcast wireless network is
>> useful as a "guest" network, so that I can give guests access to the
>> Internet without giving them access to the house net.
>>
>> Comcast is in the process of replacing all of the modems in our area
>> with these new ones.
>>
>>
>> > After the modem downloads its config from the MSO it also gets a
>> > management IP address (in theory only available from the cable side)
>> > which is used to configure and poll the device for management purposes
>>
>> There is no way to access this through the web interface. All I can see
>> is the "public" IP and the 10.0.0.1 internal one. But it wouldn't
>> surprise me if the external interface has an additional address. One
>> more reason to have another router between the Comcast device and my
>> other systems. I certainly don't trust them. Or the teenage hackers in
>> the neighborhood; how long before this "management" network is used to
>> break into somebody's house machines?
>>
>> --Greg
>>
>>
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>>
>
> The IP address of my modem is in fact 192.168.100.1. It is an Arris
> TM702G. I thought for sure it was a router and wireless access point as
> well but I never really looked at it because I had zero intention on using
> it for any of that anyway. It turns out that it just provides cable
> internet and telephony. It does support DOCSIS 3.0 (but doesn't appear to
> be using it). It seems to update the firmware on it's own because it is
> showing a build date of May 2013, and I had it installed in September 2012.
> I know I haven't updated it manually and I don't see a section in there to
> do so anyway.
>  I probably couldn't access it through my VPN because I may already be
> using that subnet here for one of our wifi networks (development or
> otherwise), but I was able to access it through my PC at home.
>  In any case, I rewired everything again (diagram link below). Now I have
> the signal from Comcast (including the MoCA filter) coming straight into
> the Motorola 2-output amplifier. One of the amplifier's output feeds to
> another Comcast-installed splitter (-3.5dBmV per output loss) that goes to
> my TVs (and Comcast set top boxes). The other amplifier's output feeds to
> the Comcast-installed coax cable that then goes into an old splitter I had
> (-3.5dBmV loss per output). One of the outputs on this splitter then goes
> to my cable modem. The other output of this splitter is connected my
> Monster Cable splitter (-7.5dBmV per output loss), which is a 4 output
> splitter. Included were 3 F-type terminators to use if you are not using
> all of the outputs. With these installed, my signal was still a bit high,
> so I removed them and these outputs are just empty. With this setup, my
> HDHR Prime signal was still showing approximately +5dBmV, give or take
> 1dBmV, depending on channel.
>  In my quest for "0.0dBmV", I then installed yet another old splitter I
> had (-3.5dBmV/output loss) prior to the HDHR Prime. So now, I have 3
> splitters in front of my HDHR Prime to intentionally drop the signal, after
> amplifying it. With this configuration, I am seeing between -1dBmV and
> +1.5dBmV, depending on channel. My cable modem is reporting 4 readings,
> depending on "DOCID", that vary between +4.48dBmV and +6.01dBmV. New
> diagram here: http://s7.postimg.org/vep1whk6j/Coax_Wiring_Home_Rewired.jpg
>  I went through and checked everything to make sure it was still working;
> internet speeds were good, Comcast set top box worked (as did OnDemand),
> and MythTV was showing me a good picture on some of the channels I was
> having issues with before (AMCHD, TNTHD). I am planning on running this for
> a week or so to determine how it works. Unfortunately because the issue has
> been so intermittent, I think I will need that long to determine if I was
> successful. The question then becomes, do I continue to utilize this
> ridiculous setup of intentionally dropping signal by using splitters or do
> I reduce the number of splitters and exchange the 2 output Motorola
> amplifier (+11dBmV boost) for a 4 port Motorola amplifier (+7.5dBmV boost)?
>
> The other option would be to just locate my HDHR Prime after a single
> splitter directly where the Comcast signal comes into my house and run a
> network cable to it as I do have an electrical outlet over there.
>
> I should connect it to my signal is from the source prior to any splitters
> just to see what signal I am receiving.  I would have done that last night,
> but I didn't have a network cable long enough.  This may be tonight's
> project.
>

It looks like you are on the right path now. I would not chase "0.0dBmV"
too hard. Signals will fluctuate. If you are a little in the positive you
should be fine.

-- 
Working on World Domination since 2001
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