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Old 24-May-2012, 10:02 PM   #1
AtLarge
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Exclamation Let's talk about signal loss.

Here's the situation.

12 unit bldg.
4 units per floor for three floors.
2 of 4 units on each floor have a shared utility room with pipe stubs in between each floor separate from each other.
Each unit has a dedicated 6 way splitter in the utility room.
Each unit would have a dedicated 2 way splitter from the main trunk to the 6 way splitter.
Antenna(s) will be in the attic no trees and relatively clear from any other buildings in all directions assumed no 110 power available up there.
Coax from the ground floor to the attic and a reasonable distance leftover for looping in each room and positioning in the attic lets say 75' total.
If there were 4 antenna's, each would supply three units in a line. #12 on 3rd, #8 on 2nd, and #4 on 1st.
Each unit has five coax outlets. 1 in each bedroom, 3 in the living room.

Considerations:
TV signal analysis here figured at 50 feet:
http://www.tvfool.com/?option=com_wr...073b1c0dbf9cd6
Winegard HD 7698P or Channel Master CM3020 from SolidSignal.com
1.4-2.0dB loss per 100' of RG6. Worst case 0.02 loss per foot = 1.5dB total.
Each outlet of the 6 way splitter will cause 3.5dB each. Avg. use per unit, say 3 = 10.5dB.
Each outlet of the 2 way splitter will cause 3.5dB each so 7dB.
Use terminators on the unused outlets in the units and on the splitters.
Total loss with this setup = 19dB.

I anticipate using one dedicated amplifier with a gain of 24dB max., variable output for each unit and cheap of course between the 2 way and 6 way splitters.

So, that gives each unit a gain of 5dB overall.
Is it ok to average it like this or should I be thinking more linear?

Example:
#12 has 12' of coax so 0.24dB + 10.5dB + 7dB = 17.74dB lost.
#8 has 24' of coax so 0.48dB + 10.5dB + 7dB + 17.74dB from the unit above it = 35.72dB
#4 has 36' of coax so 0.72db + 10.5dB + 7dB + 35.72dB + 35.72dB = 89.66dB

Therefore, the 24dB gain of the amps will only work for #12 and they will not be big enough for #8 & #4?

Actually, now that I think about it I planned for loss from 75' of coax but have only accounted for 36' getting it to the first floor #4 on the ground?

Ok, somebody throw this dog a bone. Comments, suggestions, different antenna's and amps would be appreciated.

Last edited by AtLarge; 25-May-2012 at 12:03 AM.
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Old 25-May-2012, 12:14 AM   #2
GroundUrMast
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Quote:
1.4-2.0dB loss per 100' of RG6. Worst case 0.02 loss per foot = 1.5dB total.
Actually, it's more likely to be about 5.5 to 6.5 dB per 100' in the UHF band.

Quote:
Example:
#12 has 12' of coax so 0.24dB + 10.5dB + 7dB = 17.74dB lost.
#8 has 24' of coax so 0.48dB + 10.5dB + 7dB + 17.74dB from the unit above it = 35.72dB
#4 has 36' of coax so 0.72db + 10.5dB + 7dB + 35.72dB + 35.72dB = 89.66dB
It's not clear what the last term in the equation for #8 is representing. The same is true for the last two terms in the equation for #4.

Let's start with a simple example...

Per your TVFR, KRIN, real CH-35 is predicted to arrive at your location with a predicted noise margin of +55.5 dB. If you select an antenna that has 13 dB gain at CH-35, your would have a net NM of 55.5 dB NM(air) + 13 dB(antenna gain) = 68.5 dB NM(antenna terminals).

If you place the antenna in an attic with significant penetration loss, let's say 20 dB, the net-NM would then be 68.5 dB - 20 dB = 48.5 dB NM(antenna in attic).

Then let's account for coax loss. Lets say that from the antenna to the farthest unit, you need to run 60' of coax... perhaps it needs to run part way around the building, rather than straight. Using 6.5 dB / 100' as the estimated loss for RG-6, you would budget 3.9 dB loss for the total coax run. (6.5 * 60/100).

So, at the end of the 60' run of coax in this example, your net NM would be 48.5 dB NM(antenna in attic) - 3.9 dB(coax loss) = 44.6 dB NM(end of longest run with no splitter).

A conservative estimate/budget for splitter loss is:
4 dB / 2-way
8 dB / 4-way
12 dB / 8-way
16 dB / 16-way
So, let's insert a 16-way splitter into the equation. With a 44.6 dB NM(end of longest run with no splitter) - 16 dB(splitter loss) you end up with a net noise margin of 28.6 dB at the farthest antenna outlet.

There is no need for an amplifier in this example, absent interference problems or a drastic error in the signal level prediction, you have enough signal to get the job done and still tolerate more than 20 dB of fading. (Which would imply a problem with multipath, a problem not solved by an amplifier.)
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Old 25-May-2012, 12:20 AM   #3
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My example is overly simplified, it does not account for signals coming from multiple directions and it also provides only one outlet per apartment (with four spare ports).

Consider the following... http://www.dipolnet.com/basics_of_de...ems__bib05.htm
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Old 25-May-2012, 3:03 AM   #4
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Originally Posted by GroundUrMast View Post
It's not clear what the last term in the equation for #8 is representing. The same is true for the last two terms in the equation for #4.
That was my weak attempt at taking the total loss for unit #12 and adding it to unit #8 to guesstimate what the signal strength would be for #8.

Then supposing that the total for #12 & #8 would affect the signal before it gets distributed in unit #4 at the bottom of the coax run.

Quote:
Originally Posted by GroundUrMast View Post
My example is overly simplified, it does not account for signals coming from multiple directions and it also provides only one outlet per apartment (with four spare ports).

Consider the following... http://www.dipolnet.com/basics_of_de...ems__bib05.htm
Overly simplified is good because that's exactly what I need. Now I just need to study and absorb what you wrote and that that link.
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Old 25-May-2012, 4:17 PM   #5
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Ah... you were thinking of 'daisy-chaining' splitters. A preferred system design in applications such as mid-sized and larger apartments uses a high output distribution amplifier together with feed-through taps. That's the subject of the article I linked to.

Feed-through taps are somewhat like splitters but provide high isolation between the trunk ports and the drop port(s). They have the advantage of little loss between the two trunk ports and no need to terminate the drop port(s). The down-side is that you need to engineer the system to provide reasonably equal signal levels into the distribution amplifier. Here is an example of a programmable/agile filter/amplifier intended for use in a commercial quality MATV system: http://www.dastechnology.co.uk/docs/...28SAF7U%29.pdf A calibrated signal level meter is needed to adjust the system.

In a three story twelve unit apartment, it may be less expensive and easier to maintain if you use a passive 3-way splitter at the antenna. Then run a 'trunk' to each floor. If needed, on each floor, a CM-3414 4-port distribution amplifier would provide an output to each unit. There would be plenty of signal power to drive a passive 4-way splitter in each unit.
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Last edited by GroundUrMast; 25-May-2012 at 10:47 PM. Reason: Added comment re. calibrated signal meter.
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Old 29-May-2012, 8:57 PM   #6
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Quote:
Originally Posted by GroundUrMast View Post
Ah... you were thinking of 'daisy-chaining' splitters. A preferred system design in applications such as mid-sized and larger apartments uses a high output distribution amplifier together with feed-through taps. That's the subject of the article I linked to.

Feed-through taps are somewhat like splitters but provide high isolation between the trunk ports and the drop port(s). They have the advantage of little loss between the two trunk ports and no need to terminate the drop port(s). The down-side is that you need to engineer the system to provide reasonably equal signal levels into the distribution amplifier. Here is an example of a programmable/agile filter/amplifier intended for use in a commercial quality MATV system: http://www.dastechnology.co.uk/docs/...28SAF7U%29.pdf A calibrated signal level meter is needed to adjust the system.

In a three story twelve unit apartment, it may be less expensive and easier to maintain if you use a passive 3-way splitter at the antenna. Then run a 'trunk' to each floor. If needed, on each floor, a CM-3414 4-port distribution amplifier would provide an output to each unit. There would be plenty of signal power to drive a passive 4-way splitter in each unit.
Good to know. Your right about the trunk system being the better way. I was just trying to save cable cost and separate out the cost of the amps and power to run them by each condo unit. For sure I don't want to engineer more into it than necessary. Now I see the cable is really cheap anyway so no point in cutting a corner there. It's hard to know how many will go in on this install right away. That link is good but way too deep for now.

I like that CM3414 but since it's powered, the unit on the top floor would have to supply it. Some might get chintzy about that. The 8dB gain with it though is a nice feature. I see there is an 8 port too but it would still be short four ports if we wanted to use it for the entire building.

What is your opinion of the CM3671 antenna here:

http://www.solidsignal.com/pview.asp?p=CM-3671

Overkill for this analysis? I would be pointing around 325 true to get the best of the most important channels. Do you think any of them around 180 is realistic? Suggestion for a better antenna?

http://www.tvfool.com/?option=com_wr...073b0a2a6d77f7

Is there a way to determine how many antenna's / units could be supported? I was thinking 4 antenna's would be necessary to cover 3 units each in a building. Providing the attic is open enough of course and I have found no one that has ever been up there. I do not see a dB rating in the specs for the CM-3671 so it's not clear to me how much of the antenna can be usurped.

Maybe only 2 antennas and 2 of the 8 port CM-3418 would be plenty to cover all 12 units

BTW. Here's an example of the building:



The antenna(s) would be in the part of the tallest roof line over the main entry. The picture doesn't show it very well.

Last edited by AtLarge; 29-May-2012 at 9:12 PM. Reason: More information
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Old 29-May-2012, 10:02 PM   #7
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Why not just one antenna? Then, a passive 3-way or 4-way splitter (with a 4-way you'd have a 'test' port.) That gives you outputs to three CM3414's. (The CM341X type amplifier is powered by a wall transformer that uses an F type connector... so you can extend the power connection using RG-6 cable with standard connectors. If you need to power from the floor below, no problem.)


The CM3671 seems to be over kill in this situation. Are you absolutely stuck with an attic install?
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Old 2-Jun-2012, 1:51 PM   #8
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Originally Posted by GroundUrMast View Post
Why not just one antenna? Then, a passive 3-way or 4-way splitter (with a 4-way you'd have a 'test' port.) That gives you outputs to three CM3414's. (The CM341X type amplifier is powered by a wall transformer that uses an F type connector... so you can extend the power connection using RG-6 cable with standard connectors. If you need to power from the floor below, no problem.)


The CM3671 seems to be over kill in this situation. Are you absolutely stuck with an attic install?
Avoiding a roof mount would be to everyones advantage from an eyesight and maintenance standpoint. For our area, it doesn't seem to be necessary either to get the channels we need. I get 25 channels with my attic antenna and I just use an RCA ANT751 and it's barely 3' long. I'm about three blocks away from the same location.

I'm not opposed to one antenna, in fact that would be preferred, but how much one antenna can support? The CM-3671 seemed to be the biggest, possible fit for the situation but would one antenna for twelve units be enough? That's why I considered it and two of the CM-3418's, then using four trunks and start breaking it down from there.

Would the signal loss from that many taps be significant to not work? I'm just looking for an educated guess to help shorten the trial and error routine. That and not go to the extent and $$$$ of a commercial MATV system like in that link from the UK.
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Old 2-Jun-2012, 8:04 PM   #9
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In this situation, one antenna can support many sets (if the focus is on reliable reception of the signals in the green section of the posted TVFR). Please re-read my first response.

The ANT-751 is a viable option in this situation. Though I would prefer avoiding the loss and reflection problems of an attic installation, I understand and agree with the benefit of protecting the antenna from the weather.

I've already proposed this design but let's say it a new way...

Antenna ---> Splitter (3 or 4-way) ---> Separate coax to each floor utility room to a CM-3414 (total of 3 CM-3414). There will be plenty of signal power to drive a passive 4, 6 or 8-way split in each apartment.

All of the CM-341X amplifiers are based on a 15 dB amplifier... followed by an integral passive splitter in the multi-output models.
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Old 3-Jun-2012, 2:00 AM   #10
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Ah, got it. I appreciate your input. Could save a couple bucks too then by going with the smaller antenna and super easy for one person to install alone. Thanks!
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