Can I use and assume my cable modem a Motorola SB5100 displays the actual power level of the drop in the "signal" properties?

The modem when connected to the "drop" directly displays 6db and when a 2-way splitter is installed it drops to 3db which would seem to be appropriate for the splitter reduction.

My signal levels on lower and mid channel digital QAM exceeds 80% but higher channels 112+ seem to fall off to maybe 50% +/- on a pair of TiVo's at different locations.

I would like to rewire the CATV using 2-port directional taps where the TiVo's are located to give 3-tuner capability to each location(1-connection to the display tuner and 1-connection to the 2-tuner TiVo HD machines) and then on toward two other locations with just SD cable requirements with 1-port directional taps.

If anyone is familiar with directional tap use calculations I would be very appreciative with a hand doing the math for calculating my needs!!!!!

The plan is a 4db 1-port tap with "out" to modem and the 4db forward to the first 2-port drop (30'), then forward to second 2-port drop (30'), then forward to a 1-port (20') and finally to a 1-port (20'). Cable is RG6 tri-shield using compression fittings.

If my idea is "faulted" or "ridiculous" I take criticism pretty well!!!!!

Eighty percent of what? Fifty percent of what?

Yes, the signal level indicated by the cable modem is accurate. It displays the QAM level, which is either 6dB (256QAM) or 10dB 64QAM) down from analog. Use the analog level to do your calculations.

I take it that rewiring all outlets in a homerun topology isn't feasible.

If your cable modem indicates a level of +6dBmV, take that as 12dBmV analog. I would do a DC-9, with the TAP leg feeding the cable modem and the OUT leg going to a 15dB gain drop amp.

A DC-9 loses ~1.6dB at the OUT leg, so you have 10.4dBmV at the input of the amp. Fifteen dB gain gives you 25.4dBmV out.

At 750MHz, Series 6 cable loses ~1.7dBover 30' (5.65dB/100'), which gives you +23.7dBmV at your first location. You have 3 tuners at each location, so I would utilize a DC (tap) and a balanced 3-way splitter. You're starting with 23.7dBmV and you want 5dBmV or so at the output of the splitter. At the first location, then, you need (23.7-5=) 18.7dB worth of loss. Balanced 3-way splitters lose 5.9dB, so (18.7-5.9=) 12.8, which is the approximate size of tap you want to feed that splitter. A DC-12 it is, so you have a DC-12 with the TAP leg going to the balanced 3-way splitter which then feeds your 3 tuners at that location.

A DC-12 loses 1.5dB at the OUT leg, so you then have (23.7-1.5=) 22.2dBmV heading to the next location, where you would perform the same calculations.

Specs for splitters DCs can be found at http://www.cencom94.com/gpage.html. Just click on "Specifications" under the description of the splitter or DC.

That's more than I could have asked for and I appreciate it! This is great!

Eighty percent of what? Fifty percent of what?

My TiVo's have a signal strength meter in the set-up menu that I gathered that information from. I also used a Samsung Digital tuner OTA and QAM that gave me similar results. Presently I have no "digital noise" but I did eliminate the splitter used originally(5-way) and used a 2-way (one leg) to modem and the other to another 2-way splitter to the TiVo's.

I wanted to use a Pico Macon "Tru Spec" TSC2-SB for each of the locations that have a TiVo HD and also a digital display. The TiVo's are "dual tuners" requiring one lead and the 2nd port to the display tuner. Maybe I didn't explain this very well but I believe I understood your explanation of a single port and a "balanced splitter"! Is there a preferred?

I'll try the math and if you don't mind "correct me" using the tap information from Pico Macom.

The "homerun" install could be done but I thought because I wanted 2-ports at a couple locations maybe I should just try my luck with the taps.

The taps I was interested in are displayed quite well here: http://yhst-18278607509093.stores.yahoo.net/pico-0328.html#

It would be best to homerun everything. At the locations where you need more than 1 connection, use a splitter at that outlet. Your needs may change down the road, and you may find that the current configuration doesn't meet your needs.

If your TiVo has only 1 input, then, by all means, use 2-port taps.

I see that they list the insertion loss as 1.7dB. Insertion loss varies with the size of the tap. The higher the tap value, the lower the insertion loss. Not a drastic difference, but there is a difference.

ED,


I could be "very confused"!!! Bear with me!

I thought "idealy" you would want the "least amount" of loss to the cable modem so I thought a DC-4 (if available) or a DC-6 (readily available) with the "out leg" to the modem and the "tap leg" to the amplifier OR am I not understanding here and a DC-9 using the "tap leg" to the modem gives you 9db at the modem? I thought if I had a 12db "drop" and I used a 9db "tap" it would result in 3db to the modem. Am I confused here? It seems my thoughts are errored here! I'm glad I asked for help!

Does knowing now that the TiVo's are "dual tuners" and needing only 2-port taps change the math?

I'd like to use Pico Macon "TruSpec" taps and amplifier just because the seem to be readily available!

If you would be so good as to do the math one more time for me it would be appreciated.

The amp I might want to use is here: http://yhst-18278607509093.stores.yahoo.net/pico-0051.html

The taps are all here: http://yhst-18278607509093.stores.yahoo.net/products-distribution-passive-component-taps.html

From the drop I'd like a 1-port tap (TSC-SB) to modem and amp (which leg to which component), the amp (CDA-1P), a 2-port tap (TSC2-SB) to another 2-port tap (TSC2-SB), to a 1-port tap (TSC-SB) ending at the final 1-port tap (TSC-SB). I can make every port to port equal at 25' if that helps me understand what I'm doing. I just need tap values if you don't mind!

ED,


I could be "very confused"!!! Bear with me!

I thought "idealy" you would want the "least amount" of loss to the cable modem so I thought a DC-4 (if available) or a DC-6 (readily available) with the "out leg" to the modem and the "tap leg" to the amplifier OR am I not understanding here and a DC-9 using the "tap leg" to the modem gives you 9db at the modem? I thought if I had a 12db "drop" and I used a 9db "tap" it would result in 3db to the modem. Am I confused here? It seems my thoughts are errored here! I'm glad I asked for help!

Does knowing now that the TiVo's are "dual tuners" and needing only 2-port taps change the math?

From the drop I'd like a 1-port tap (TSC-SB) to modem and amp (which leg to which component), the amp (CDA-1P), a 2-port tap (TSC2-SB) to another 2-port tap (TSC2-SB), to a 1-port tap (TSC-SB) ending at the final 1-port tap (TSC-SB). I can make every port to port equal at 25' if that helps me understand what I'm doing. I just need tap values if you don't mind!

That's incorrect in thinking that you need the most signal to the cable modem. Cable modems work just as well whether the input signal level is +12dBmV, 0dBmV, -12dBmV or anywhere else within that range. Actually, specs go from -15 to +15dBmV, but you don't want to be right on the edge. Three dB is a good headroom to maintain. One of the upsides of putting the cable modem on the TAP leg is that it forces the cable modem to transmit at a higher level, thus helping it to be heard above any noise that might be present on that outlet.

The way taps work is that the level at the TAP leg is the input minus the tap value. So, yes, there would be (12-9=) +3dBmV at the cable modem. You cannot ask for any better than that.

The signal level at the OUT leg is the input minus the insertion loss of the thing. According to their website, Pico taps have an insertion loss of 1.7dB. Now, I've looked at a lot of spec sheets from various manufacturers, and I have never seen one that has the same insertion loss for all tap values. Tap values of 16dBmV and up are usually the same (.8-1dB), but as you go below 16, the insertion loss stats to increase. Not dramatically, but it does increase. With the above example of +12dBmV at the input of the DC-9, you would have (12-1.7=) 10.3dBmV at the OUT leg.

Just use my first example (I gave you a good head start), pull out your calculator, and go to town. You have 25.4dBmV coming out of the amp and go down 30' of cable, which loses 1.7dB (5.65dB/100'), which gives you 23.7dBmV at the first location. You want 5-10dBmV at the outlet, so (23.7-5=) 18.7 is the approximate size of the tap you would need. A 20 would put you below 5dBmV, so a 16 is what you would want to put at that location.

The insertion loss is listed as 1.7dB, so (23.7-1.7=) 22dBmV is how much signal you have to go down the line to the next outlet, where you would perform the same calculations all over again, and so on to the end of the line.

Make sure you terminate the OUT leg of the last tap.

ED,

I believe I've absorbed most of this and I'm going to do "specific" lengths required and move along! It will be probably Monday or Tuesday evening but I'll post my math and I'll let you grade me!

I've played with some install using maybe a 3 way splitter after the amp using one leg for each location requiring the 2-port tap and moving forward with the third to the balance of the outlets that only need conventional cable outlets. If I used the 3-way and a 2-port tap is all I need to do is make sure I use "terminators" at each tap?

I think I've got the drift now of the "tap values", are they "more or less" just "attenuators"?

I appreciate your time!

-Dave

ED,

I believe I've absorbed most of this and I'm going to do "specific" lengths required and move along! It will be probably Monday or Tuesday evening but I'll post my math and I'll let you grade me!

I've played with some install using maybe a 3 way splitter after the amp using one leg for each location requiring the 2-port tap and moving forward with the third to the balance of the outlets that only need conventional cable outlets. If I used the 3-way and a 2-port tap is all I need to do is make sure I use "terminators" at each tap?

I think I've got the drift now of the "tap values", are they "more or less" just "attenuators"?

I appreciate your time!

-Dave
Dave,

Since the outlets could be homerun, it would be better if you ran the outlets that way. You have 4 locations (not including the cable modem), so use a 4-output amp to feed the outlets. Coming out of the amp would be 7dB more that what goes in (multiple output amps are merely a standard 15dB gain amp with a splitter on the output). So, you would have (10.7+7=) 17.7dBmV coming out of each port of the amp to go to each outlet. Perfect. At the outlets where you need 2 connections, just use a 2-way splitter. Or, if you would rather, use the 6dB 2-port taps. Just make sure you terminate the OUT legs.

Save yourself some money and get your amp here (http://www.cencom94.com/gpage4.html), and the splitters and tap for your cable modem here (http://www.cencom94.com/gpage.html).

Well ED,

I'm struggling with the 2-port taps and it looks like I'll need to order them from the "left coast"! I'm going to do it with the splitters at the two locations for the time being and order the 2-port taps if they're not here by the 27th. When the taps arrive I can just do the taps and wall plates over. I think I'll lay this all out on the floor first and do the connection to the first outlet and then see what the results are on the higher QAM frequencies.

I thought I had found everything at one location and the fellow called me back and didn't have the 2-port taps. I did get a pretty good deal I think on a quality 4 port amplifier by "Extreme"! They've engineered replacement modules for their line and these are on a close-out from their earlier line.

Here's the amp: http://www.sunsetenterprises.com/subcat2.asp?S2=Amplifiers%2E&S=Drop+Installation+Material&C=Clearance&CAT=CLEARANCE


I spoke with Jeff there and it was a "very pleasant" exchange. The convenience is one day ship UPS to me. Jeff broke 50 piece packages to give me what I needed for terminators, compression fittings and some F-81's. Good people!!!!!

Here's the newer Extreme line: http://www.extreme-broadband.com/index.asp

Dave,

Good luck with it all.

Since you got a 4-port amp, are you doing it homerun?

Ed,

This is going to take "some time"! I received my taps today and I was invoiced for 2-port but received 1-port. They're fixing that "no charge" but there will be little or no progress this weekend to "completion"!

I did however "tinker"! I removed the splitter that was doing the modem and the tuners, replacing them with a 9db tap(tap to modem) out(to tuners). There had been a 4-port splitter for whole house next and I replaced it with the 2-port splitter I had removed from the modem etc. Here's the results: Modem went from: Downstream SNR 39/ Power level 4 to SNR 39/ Power level -2db. The tuner on the TiVo(0-100%) values increased 15-20 points on average. That change alone is a significant difference numerically.
The mid QAM's 70-80 are "pegged" at 100%, higher QAM's 84-93 are 95+ and the higher 112-115 have improved dramatically to higher 80's or 90+. What was barely 50 is now in the upper 80's and 90's! That was a $1.65 tweak!

The amplifier is still in "the box"! I'll have the 2-port taps next week and I can do more with it. One other thing to mention, the tuner that I checked is running off of the RG-59 that was there from the original house build. That will be replaced with RG-6 when I do the amp and 2-port taps. I would guess that run is 20+ feet. I haven't checked the tuner that is on an RG-6 from the splitter.

The setup is 9db tap to modem, out to 2-way splitter, 20+ feet (RG59) to TiVoHD tuner 1, 30+ feet (RG6) to TiVoHD tuner 2. The rest of the house (analog) is without "signal"!

Your thought's on the cable modem values?

-Dave

Ed,

Your thought's on the cable modem values?

-Dave
Excellent!!!

Keep your upstream between 35 and 50 and downstream between +8 and -8, then you'll be OK.

And giving your TV sets too much signal will distort the picture. With 12 db input, you have enough signal for 4 outlets, even 5 depending on the lenght of your outlet.

And giving your TV sets too much signal will distort the picture. With 12 db input, you have enough signal for 4 outlets, even 5 depending on the length of your outlet.

I pretty much understood going in that I didn't want to "over power" the tuners but the wiring available was RG59 and not very accessible. I also really wanted the 2-port outlets at the two primary locations. The taps and the new cabling will be very accessible and taps are very inexpensive so the "system" can be "tuned" if need be. I included a 4 port amp so that I could add to the system easily. One or two of the amp ports will likely not be used unless there are a couple rooms added.

Thanks for the #'s relating to the modem. They confirm what Ed had pointed out and what I was told previously!

Ed,

This is great. I did the 2-port tap install today with the 4-port 15db amp etc. I've now got 2-ports at each DTV that has a TiVo HD, a port for the tuner in the TV and a port for the 2-tuner TiVo HD's also. Each location with a TiVo can record 2 and you could watch "live" TV through the DTV tuner or watch a recorded program using the TiVo's that are "networked" with CAT5 rather than the wireless option.

The QAM signals on each machine's tuner and the TiVo's tuner are all 90% + on a 100% scale. I did a mix for the install. Each DTV/TiVo location is a homerun from the 4-port 15db amp to the 9db tap that is terminated at that point. The rest of the TV's in the house are being run from a port on the amp to a 4-way splitter that uses the original RG-59 that was a homerun install in '93 I believe.

Everything seems great except wall plates. I've got one done with a tap and a CAT5 and need to buy another to finish the job and all seems well.

Glad it's all working out for you!