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Streetlight

join:2005-11-07
Colorado Springs, CO
reply to EG

Re: [Signals] Modem signals better when split twice on highdB le

Thanks, EG. I'll look around for a forward path attenuator. Just what I need.

What about whamel's situation: no rise in the upstream power level. I guess we need to know the model of splitters being used. In my case I used Extreme Broadband Engineering's splitters which are what Comcast uses in our area. Are there forward path only splitters? I've not heard of them.

My levels after rewiring were, on 4 down channels, at about 9.5 dBmv and 3 up channels at about 42 dBmV. After adding an extra 2-way 3.4 dBmV splitter, I got an OK compromise of down of ~5 to 6 dBmV and up ~45.5 dBmV. My experience here is that on my Zoom 5341J modem if up goes close to 50 dBmV, problems occur and with our high summer temperatures, I didn't want to push my luck with another 3.5 dBmV of attenuation and have enough headroom for these signal level changes due to temperature and other causes . Also, it may be that this modem is very sensitive to upstream high power. So far, I've had absolutely no Internet problems with my current setup.
--
There is nothing more deceptive than an obvious fact.

Sherlock Holmes in
The Boscombe Valley Mystery
A. C. Doyle
Strand Magazine, October 1891



whamel
billhamel .net
Premium
join:2002-05-09
Hinsdale, IL
kudos:10
Reviews:
·Verizon Broadban..
·AT&T U-Verse
·Comcast

If you notice, the second (bottom) picture where I used the -3.5dB leg, the DOCSIS 1.X freq 29.5MHz increased 3dBmV. I know for a fact I use that frequency. I have another modem UBEE DDM3513 that is provisioned on the same line in my apt (I have 2 internet connections) and it it says I config. page says I use that upstream frequency. Weirdly enough, after re-wiring and installing a new passive 3-way splitter, the downstream frequency switched from channel 1 to channel 4 which means I go from 669MHz to 663MHz.
Can't seem to figure it out because I know certain areas are provisioned on a certain frequency to avoid "crowding" and loss of speed and signal quality. In Hattiesburg, MS we have 4 downstream channels available to us and only 2 upstream.
I have just noticed that while I was in Chicago, (my mothers home in the burbs) her modem had 8 downstream channels and 4 upstream. But that forward-path attenuator sounds like a good option.
Thanks for the suggestion.
-Bill
--
Bill - Hattiesburg, MS - »www.billhamel.net



Streetlight

join:2005-11-07
Colorado Springs, CO

whamel, and EG

Oops, I didn't notice the 2nd QAM signal had gone up in your changed setup. Not sure, then, why the higher upstream frequency was attenuated and not the lower.

I found the manufacturer's spec sheet for these things and it seems that there is some small attenuation back for frequencies below 65 MHz of 1 to 1.5 or 2.0 dBmV, but at higher frequencies they have the labeled attenuation. That is, a 6 dBmV one will attenuate 6 to 7 dBmV at 88 MHz and higher. Generally, that would be OK for internet frequencies - upstreams are 25-36 MHz, downstreams are 580-606 MHz on my modem - but maybe not the higher frequencies used for cable TV since there's no data for >860 MHz. This suggests that these things should be plugged in to the cable input of the modem and definitely not at the input to a splitter that my connect eventually to a cable box.

I found a UK blog that shows these attenuators attenuate both up and down streams:

»www.cableforum.co.uk/board/12/16···int.html

These results leave me with some questions about how well these things work.
--
There is nothing more deceptive than an obvious fact.

Sherlock Holmes in
The Boscombe Valley Mystery
A. C. Doyle
Strand Magazine, October 1891


EG
The wings of love
Premium
join:2006-11-18
Union, NJ
kudos:10

Too much is being read in to this IMO... The forward path only attenuators that I have perform fine and DO NOT attenuate the return path.. Perhaps they introduce 0.1 dB of attenuation in to the return path which is insignificant.



whamel
billhamel .net
Premium
join:2002-05-09
Hinsdale, IL
kudos:10
Reviews:
·Verizon Broadban..
·AT&T U-Verse
·Comcast
reply to Streetlight

said by Streetlight:

whamel, and EG

Oops, I didn't notice the 2nd QAM signal had gone up in your changed setup. Not sure, then, why the higher upstream frequency was attenuated and not the lower....
I found a UK blog that shows these attenuators attenuate both up and down streams:

»www.cableforum.co.uk/board/12/16···int.html

These results leave me with some questions about how well these things work.

I found attenuator "conditioners" that worked on both up and down stream. Was very confused about those. I will have to find the website again...
--
Bill - Hattiesburg, MS - »www.billhamel.net