Need Help With Our CATV System - Too Many Amps & Splitters

[spinjector]

Hi all,

I need some help with our cable TV distribution system. We recently installed a bunch of new flastscreens in our studios, bringing the total up to 19. Signal dropout is getting to be a problem, and Comcast just can't get the amps & splitters set up correctly.

We a video DA with about 24 outputs, which can pass the two-way data that the set-top cable boxes need for channel authorization and on-screen guides. It also needs to pass regular cable and free-HD for the flatscreens in the conference rooms that do not have the set-top boxes.

Does anyone have any suggestions for a specific model of video-DA that I can take a look at?

*Note that I might already have what I need. I found a DawnCo LNB-DA in a storage room. It's this model here: http://www.dawnsat.com/auto_links/pdf/DIVINSUP-1X16AE.pdf

Is 950-2450mhz enough bandwidth for cable TV, HD, and the two-way set-top box communication?

Thanks.

 

[PTBoardOp94]

In the classic analog cable setup, you'd need everything down to the VHF frequencies to be passed. Cable channel 2 was delivered on 54 MHz. I'm not sure if Comcast Digital cable requires this or not, but I would believe so.

I don't know of any video DA products offering that many channels. The largest I know of is 8 channels: http://www.yourbroadbandstore.com/product.php?pid=712487

 

[fybush]

You may well need to be able to go below 54 MHz, too, if the cable box needs to talk back to the headend, or if you're trying to pass cable internet to a modem.

 

[OttoM]

I think you're overcomplicating things.

You're going to need an amp that passes 2MHz-1GHz (or so). Something like this: http://www.summitsource.com/product_info.php?ref=1&products_id=7756 (although that's an 8-port).

And you say Comcast can't figure this out? THAT'S scary. Maybe Larry The Cable Guy can help!

 

[JamieD]

CATV uses 5-42mhz for the return path and 50Mhz to 1000Mhz for the forward. At each set you should have between 0 and 15 dBmv on the analog channels and about 6dBmv less on the digital muxes for it to work correctly. If analog drops below 0dB at any point you start to drop into the noise floor. Amplifiers need to be 2-way capable and with that many outlets you will need one with an active return that will amplify both directions. All the outlets should be home-run wired to a central location where the amps and splitters will be. The outside feed should go into the amp first and then into the splitters or taps to connect the outlets. Something like this http://www.hollandelectronics.com/catalog/catalog.php?product_id=HCDA-Series-Drop-Amplifiers should do for an amp. I would feed the output to a good 4-way splitter and each output from that into an 8-way giving you enough spigots to connect 24 outlets. This assumes the outside signal is good and that the runs to the outlets are not too long. RG-6 cable will lose about 1.5dBmv at 50mhz and about 7.5dBmv at 1000mhz /per 100 feet. If the runs are long you will need an amp with more gain and a slope control to compensate for the cable loss. You should have a catv field strength meter to set this up correctly.
I'm don't know about Comcast, but here the CATV company will install, repair and provide the needed equipment at no cost for any service you are subscribing too.

 

[stephend2]

do all the drops come back to a single location or is there a loop around the building?

what i did in an apartment tv setup is put an amp in every building, tuned the slope for the middle of the building, set the output to give a sufficient singnal at the far end of the building and add some attenuation for the middle and close end. 24 units in each building, ran out of amp to a 3 way splitter then to three 8 way splitters. The drop to each apartment has a 4 way splitter hanging off it so i took that into account.

end result was +5 - +10 dbm at all jacks. I was able to get everything perfect as i built the headend, tuned and balanced it myself and designed the whole distribution system as the property was being built.

Whatever amp you get, make sure it has a return amp as well or your return signal will end up getting lost before it makes it back out. I had that situation with a cable modem one time. Blonder Tongue makes some good amps, so does PDI.

I actually prefer the PDI amps as they run cooler and seem to be more reliable. I've had a few Blonder Tongue amps die on me. Never had so much as a glitch out of anything PDI. Stay away from Pico Macom! We had some of their modulators when the system was first built, almost all of them died in the first year, replaced them with a mix of Blonder Tongue and PDI and haven't had a seconds trouble since. It's been over a year since I've even been out on a trouble call for that system.

 

[spinjector]

Cool, thanks guys. Now I know the type of product I need.

I've been looking at all your links, and reading specs & applications, and this has helped my understanding a lot.

I have some further questions:

1) Does anyone know of one of these amps that's rack-mount and has at least 16 outputs..? I'd like to put it in the sat-rack.
2) Or - just a plain passive rack-mount splitter with 16+ outputs that I can feed the amp into?
3) If I wanted to pick up a simple hand-held cable TV signal strength meter/analyzer, what should I look for? Any specific product suggestions?

Just for clarification, this is what we have: Coming up through the utility shaft in our building is a thick hard aluminum coax about an inch in diameter. At each floor, there's a heavy junction box with about a dozen water-tight fittings for smaller hookups. Coming from that we have four thinner feeds of something called "Q241" (I might have the name wrong); it's like the thicker stuff in the shaft, but thinner and flexible. The Q241 transitions to RG-6 for all home-runs and splits to the TV sets. Each of those Q241 four feeds go to:

• (2) Business-class cable modem/routers sharing a single splitter.
• The cluster of ~8 sets in the newsroom that are still CRT.
• The ~8 flatscreens in the lobby, offices, & conference rooms (a less important part of the problem.
• The ~12 new flatscreens in the studios with cable boxes (the focus of the problem).

It's the flastscreens & cable boxes that are having problems. The HD randomly drops out and the onscreen guides fail to update.

That part of the system is as follows:

• (3) HD-capable flatscreens without cable boxes.
• (3) HD-capable flatscreens with cable boxes + the works: digital, HD, onscreen guides, & the HD-sports package.
• (4) HD-DVR boxes in various locations for recording news & sports events.
• (~4) straggling CRT toobs in the edit booths.

FYI, the cable modems are SMC brand, one being the new 50 Mbps model, and I can access the RF info its Status page in my web browser, as follows:

Downstream Frequency 614.998413 MHz 620.999634 MHz 627.000977 MHz
Lock Status Locked Locked Locked
Modulation 256 QAM 256 QAM 256 QAM
Symbol Rate 5.360537Msym/sec 5.360537Msym/sec 5.360537Msym/sec
Downstream Power 0.888837 dBmV 0.442348 dBmV 0.362933 dBmV
SNR 36.386890 dB 36.386890 dB 36.386890 dB

Upstream Frequency 31599985 Hz
Lock Status Locked
Modulation 16QAM
Symbol Rate 5120 KSym/sec
Upstream Power 37.6800 dBmV
Channel ID 8

 

[stephend2]

http://www.multicominc.com/active/comparison/indoor_distr_amps/bida_100a_30.pdf

there is a good amp, if you order from multicom, talk to Dominic.

then you would need a rackmount splitter or combiner - the combiner would be the easiest to come by and you can just use it as a splitter.

http://www.multicominc.com/active/comparison/combiners/pc_series.pdf PC1601 would be a 16 way passive combiner which all you would have to do is connect the output of the amp to the output of the combiner then use the inputs as the outputs.

you will need a catv signal meter to set this up properly and might even want to put a slope on the signal to compensate for long runs of RG6 depending on the length.

 

[necrat123]

CATV uses 5-42mhz for the return path and 50Mhz to 1000Mhz for the forward.

The two big operators here are 5-850. The "pole mounted" (guy wire) amplifiers can not handle above ~850MHz without excessive noise and the level drops.

 

[JamieD]

CATV uses 5-42mhz for the return path and 50Mhz to 1000Mhz for the forward.

The two big operators here are 5-850. The "pole mounted" (guy wire) amplifiers can not handle above ~850MHz without excessive noise and the level drops.

Here everything new is being build to 1ghz with only passives beyond the optical node. The appetite for HD is gobbling up bandwidth quickly.

 

[JamieD]

CATV uses 5-42mhz for the return path and 50Mhz to 1000Mhz for the forward.

The two big operators here are 5-850. The "pole mounted" (guy wire) amplifiers can not handle above ~850MHz without excessive noise and the level drops.

Here everything new is being build to 1ghz with only passives beyond the optical node. The appetite for HD is gobbling up bandwidth quickly.