Splitting the OTA signal - how much before amplification is needed? - AVS Forum
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post #1 of 23 Old 12-17-2012, 12:56 PM - Thread Starter
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I have a rooftop antenna for picking up local digital stations and may have maxxed out on splitting the signal without amplification. I don't know how to tell other than that there are a few channels I've been receiving steady and strong for over 10 years that have begun dropping out since adding an HDHomeRun Dual into the system.

Up until the addition of the HDHR3 Dual, I had 50 feet of cable from the antenna to a thru-the-external-wall-of-the-house fitting, then about 3 feet to a 2-way minimal loss splitter where one side goes about 6 feet to the OTA connection of a TivoHD and the other side runs about 6 feet before connecting to a wall jack. From the first wall jack there is a 30 foot run to a wall jack in a family room with the signal split again to a second TivoHD and a PC tuner.

Schematically it looked a little like this:

Rooftop Antenna
|
50 feet
|
house jack plate
|
3 feet
|
2-way splitter #1 - - - - - (6 feet) - - - - - TiVoHD #1
|
6 feet
|
Wall Jack #2
|
30 feet
|
Wall Jack #3
|
3 feet
|
2-way splitter #2 - - - - - (6 feet) - - - - - - TiVoHD #2
|
6 feet
|
PC (Hauppauge HVR-1600)

Things were working well with this configuration.

Then I added the HDHR3 Dual which simply changed the first 2-way splitter to a 3-way splitter. At least 2 stations that had been consistently stable became marginal. The 3-way splitter I selected was the Channel Vision HS-3 from Parts Express (http://www.parts-express.com/pe/showdetl.cfm?partnumber=183-132). The 2-way splitter it replaced was a very good one provided to me by our cable technician who came to strengthen our cable distribution in the house.

So perhaps I'm splitting the signal up just a little too much, but I don't have actual measurements - just the symptom of marginal reception of a couple channels. What do you think?

If I need to amplify the signal, what's the best way to do it? How much amplification do I need and where should the amplifier go? I'm hoping that I can do it inside the house (after the 50 foot run from the antenna), but I want to do what's best if it's not too inconvenient.

Thanks!
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post #2 of 23 Old 12-17-2012, 02:09 PM
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Your question, as asked, is like someone saying "I'm going shopping. How much can I spend before I run out of money" before they check to see how much money they have.

In other words, you can keep right on splitting and running cable right up to the point where it fails. Then you need to back up and re-evaluate or take other corrective action.
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post #3 of 23 Old 12-17-2012, 03:18 PM
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My RG-6 cable run is about 100' from antenna to the garage where it connects to a drop-amp signal booster. From there the output line is immediately (and I mean about 3 inches) connected to an old Monster 3-way splitter (which was given to me. I'd never purchase a Monster product) balanced at -3dB (I think) for each line out. From there, the cable lines use the old RG-56 cable runs and go to their various wall plates. 3 tv's (one HDTV and two analog with digital boxes) and all tv's get the same signals nice and strong with no issues. I'd look at the markings on the good 2-way splitter and see if you can figure out who it is and if they make a 3-way splitter.
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post #4 of 23 Old 12-17-2012, 03:50 PM - Thread Starter
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Quote:
Originally Posted by ProjectSHO89 View Post

Your question, as asked, is like someone saying "I'm going shopping. How much can I spend before I run out of money" before they check to see how much money they have.
In other words, you can keep right on splitting and running cable right up to the point where it fails. Then you need to back up and re-evaluate or take other corrective action.
For the sake of discussion, let's just assume that like most others I hope to solve this issue spending as little out of pocket as practical.

I have a very satisfactory signal after my first 2-way splitter and am interested in opinions on a reasonable approach in trying to go to a 3-way (or 4-way if I were to add another HDHR3) splitter. I'm cautious about indiscriminately boosting a "good" signal more than about 15 dB for concerns of introducing undesirable noise, but perhaps that's not a legitimate concern(?).

I don't imagine I'd want a pre-amp (prior to the 50-foot run from the antenna), but I'd like to know what others think. Are there some ways of distributing a good signal that are more cost-effective than others? Are all splitters created equal? I seem to recall seeing a 3-way that had a 2.5 dB drop on one output and 3.5 dB drops on the other two, but I don't know if that's typical or if it was a special case. How about the wall jacks? Is there a measurable drop for each jack/connection used? Is there any advantage in bypassing jack plates in lieu of running uncut cable straight to its next point of use (i.e. my last splitter)?

If I were to use something like this Electroline EDA 2400 4-port RF/CATV Distribution Amplifier at the first splitter, would that likely be enough of a boost to prevent needing any more amplification? Is there any advantage to a device like that over using the more modular approach of an in-line amplifier (like this 1 GHz RF Cable and Off Air TV Signal Amplifier 10 dB) just before a standard unamplified 3-way splitter (which I already have)?

Thanks!
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post #5 of 23 Old 12-17-2012, 06:00 PM
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Without knowing what the power levels of the signals are from the antenna, the calculations cannot be made.
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post #6 of 23 Old 12-18-2012, 12:23 AM - Thread Starter
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Quote:
Originally Posted by ProjectSHO89 View Post

Without knowing what the power levels of the signals are from the antenna, the calculations cannot be made.
Can you point me in the right direction for obtaining the needed "power levels" for making these calculations? I get signal strength bars from the TiVoHD and the HDHomeRun (with the Signal Meter app), but this isn't what you're talking about, is it?

One of my channels (local ABC affiliate) continues to give me a very strong steady signal (88-90 on the furthest downstream TivoHD, and maxxed-out on the HDHR Signal Meter app), but it's the one and only channel that no longer gives me a steady picture. I'm getting frequent dropouts on that channel ever since switching out the 2-way splitter for the 3-way splitter. If this is a multipath issue, boosting it probably won't help me, right? If I could get that one issue resolved, I wouldn't even sweat the other stuff. Any thoughts on how I should troubleshoot this issue?

I'm also still curious about the question I posed above: Is it generally preferable to use a distribution amplifier instead of a single output amplifier with a discrete splitter?
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post #7 of 23 Old 12-18-2012, 04:17 AM
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No, those indications are not useful for performing a loss budget calculation.

We can get a good estimate of signal powers if you post an exact location TVFool plot, identify your antenna (need gain figures) and its mounting location, and the weakest channel on the TVFool plot that is needed.
Quote:
Is it generally preferable to use a distribution amplifier instead of a single output amplifier with a discrete splitter?

From a signal standpoint, it matters little. However, the integrated units are generally a more mechanically reliable since they don't require the external coax connections.
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post #8 of 23 Old 12-18-2012, 11:38 AM - Thread Starter
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Quote:
Originally Posted by ProjectSHO89 View Post

No, those indications are not useful for performing a loss budget calculation.
We can get a good estimate of signal powers if you post an exact location TVFool plot, identify your antenna (need gain figures) and its mounting location, and the weakest channel on the TVFool plot that is needed.
....
Here's the tvfool plot for my house.

I have a Channel Master CM-4221 mounted at the top of two 6-foot masts rachet-strapped to our chimney, putting it at about 20 feet high. It is aimed to the SW at almost exactly 220°.

I don't need any channel below what's in the green, but I like to get channel 13 in the yellow (it has a Low Power "mirror" at channel 22 near the top of the list, but that's new to me and I've been getting dropouts on it) because it's been historically very steady. The channel I'm having the most trouble with is channel 38 (near the top of the chart). Channels 39 and 48 (CBS and NBC affiliates) are right next to it and haven't even blinked.

Note (Don't know if this is useful or not): The neighbor directly south of us has two huge maple trees in his back yard at about 50 feet and 200° from the antenna (of course all the leaves are gone right now, but it's never seemed to present a problem even in mid-summer).
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post #9 of 23 Old 12-18-2012, 02:51 PM
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Try lowering the antenna in 6" intervals to see if you can get out of those several dead spots for certain channels.

Getting that VHF-13 signal with a UHF antenna is probably an unreasonable cause. Go for the UHF 22 signal instead.

Ironically, I have seen cases where bare trees permit new problems to arise that weren't there during the summer.
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post #10 of 23 Old 12-19-2012, 04:42 PM - Thread Starter
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Quote:
Originally Posted by ProjectSHO89 View Post

Try lowering the antenna in 6" intervals to see if you can get out of those several dead spots for certain channels.
Getting that VHF-13 signal with a UHF antenna is probably an unreasonable cause. Go for the UHF 22 signal instead.
Ironically, I have seen cases where bare trees permit new problems to arise that weren't there during the summer.
Thanks for the suggestion - with the higher-is-better mindset I was not considering lowering it to find a clearer "window". I'm hoping for a chance to give this a try over the weekend.

Having received channel 13 with this antenna forever, it had slipped my mind that it was still in the VHF range. I may have to rotate the antenna a couple degrees to aim it more towards the channel 22 tower.

Interesting - I hadn't thought of it before, but I can visualize leaves on a tree having a slight slow-down-and-spread-around effect on these waves that might permit an antenna to better pull them in.
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post #11 of 23 Old 12-19-2012, 05:31 PM
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Keep in mind that a big tree is not a static thing. It will grow and branch out as it were, so what works this year, might not work well next year or the year after.
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post #12 of 23 Old 12-23-2012, 10:41 AM
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Others here truly know their enginnering but here is how I see his situation:

He's got the loss form coax losses at the extreme end of the coax run. The loss depends on the frequency but his strength is down to about 25% just from that. Then first splitter and the signal is down to 1/8. Then a second splitter and the strength is down to 1/16 of what it is at the antenna.

He might/tshould consider a second antenna to serve the Hauppage and Tivo but ony if his house layout works really well for it (an easy installation). Obviously another antenna takes alot more hours than simply screwing in an amplifier.

Yes he should do marginally better with a three way splitter over the pair of two-way splitters.
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post #13 of 23 Old 12-23-2012, 10:57 AM
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You've got over 30dB of signal strength difference between your two strongest stations and your network locals. When you amplify signals that have that much difference in signal strength, the stronger ones can start beating up the weaker ones, even when the amplifier is running within its maximum input power range, so if you do choose to amplify, you should go with the 10dB amp, and you should also put an inexpensive HLSJ filtering device on the input side of the amp so that local FM does not intermodulate with the TV signals.
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post #14 of 23 Old 12-23-2012, 11:06 AM
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Avoid using fractions or percentages since they don't accurately reflect the scale of the signal differential and they tend to unnecessarily "freak out" those who don't understand what's going on. For example, the dynamic range of the digital signal under ideal conditions is about 80 dB. That's 1 X 10 to the 8th power difference between the weakest to the strongest that could be used. In the real world, 50 - 60 dB (100,000x - 1,0000,000x) range is often a more useful number to expect in strong signal areas. Now, how many times can you divide that signal in half or by 1/16th or whatever before you run out of signal?

That's why we use decibels.
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post #15 of 23 Old 12-23-2012, 11:13 AM
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Seems like I answered something very similar to this last week....

If things were OK before you replaced the first 2-way splitter with a 3-way splitter:
All splitters are just different combinations of two way splitters.
The 3-way splitter will have two of them cascaded inside it, and (hopefully) is marked to show which port is which. The first split inside it will be a 2-way split, and will only drop the incoming signal by about 3 to 3.5 dB. The other split from that first one, goes to another 2-way split, so those two outputs will be down about 7 dB.
To keep things balanced, just connect the two DIRECT feeds (those that are not split again) to the same places as before. Then, use the "-3.5 dB" (sometimes labeled the "high" leg on the splitter) to the run that gets split again someplace else. You are probably splitting one of the two low-output legs of the 3-way in a second splitter, so that's why it's weak.

Either way, you are really close to not having enough signal for really reliable reception. A bigger/better antenna might help. A low-gain (maybe 7-10, or 15 dB of gain) distribution amplifier might help.
Most distribution amps are simply a 15 dB gain amplifier, and they have a two-way (-3.5 dB loss) splitter, a 4-way (-7 dB loss), or an 8-way splitter (-10.5 dB loss) or no splitter at all ("single output"), built in to the same box. You simply decide where you want to do the splitting, and buy accordingly...including external splitter, if needed.

Also, remember that signal levels will vary over a daily cycle, as well as a yearly cycle. That's normal atmospheric attenuation, which depends on temperature and humidity in the air. The best signal strength will be on a winter morning, lowest signal will be a summer afternoon. Trees make it even worse, as they bloom foliage.

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post #16 of 23 Old 12-24-2012, 07:37 AM
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Quote:
Originally Posted by kenglish View Post

Seems like I answered something very similar to this last week....
If things were OK before you replaced the first 2-way splitter with a 3-way splitter:
All splitters are just different combinations of two way splitters.
There are balanced 3-way splitters. They lose ~5.5dB (5MHz) to ~6.5dB (1GHz) on each leg.

CIAO!

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post #17 of 23 Old 12-28-2012, 01:54 PM - Thread Starter
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Quote:
Originally Posted by kenglish View Post

Seems like I answered something very similar to this last week....
If things were OK before you replaced the first 2-way splitter with a 3-way splitter:
All splitters are just different combinations of two way splitters.
The 3-way splitter will have two of them cascaded inside it, and (hopefully) is marked to show which port is which. The first split inside it will be a 2-way split, and will only drop the incoming signal by about 3 to 3.5 dB. The other split from that first one, goes to another 2-way split, so those two outputs will be down about 7 dB.
To keep things balanced, just connect the two DIRECT feeds (those that are not split again) to the same places as before. Then, use the "-3.5 dB" (sometimes labeled the "high" leg on the splitter) to the run that gets split again someplace else. You are probably splitting one of the two low-output legs of the 3-way in a second splitter, so that's why it's weak.
Either way, you are really close to not having enough signal for really reliable reception. A bigger/better antenna might help. A low-gain (maybe 7-10, or 15 dB of gain) distribution amplifier might help.
Most distribution amps are simply a 15 dB gain amplifier, and they have a two-way (-3.5 dB loss) splitter, a 4-way (-7 dB loss), or an 8-way splitter (-10.5 dB loss) or no splitter at all ("single output"), built in to the same box. You simply decide where you want to do the splitting, and buy accordingly...including external splitter, if needed.
Also, remember that signal levels will vary over a daily cycle, as well as a yearly cycle. That's normal atmospheric attenuation, which depends on temperature and humidity in the air. The best signal strength will be on a winter morning, lowest signal will be a summer afternoon. Trees make it even worse, as they bloom foliage.
I've seen 3-way splitters that showed the drop on each output, with one being less than the other two, the ones I have (Channel Vision HS-3) seem to have no markings at all, but its specifications state that there is a 5.5 dB insertion loss. I had assumed that meant all three outputs were balanced and had an equal loss. If that is the case, would it be a reasonable gamble to try a simple and fairly conservative in-line amplification of about 10-15 dB in front of the 3-way splitter? Something like this Channel Master CM-3410 (http://www.solidsignal.com/pview.asp?p=cm3410&d=channel-master-cm3410-ultra-mini-distribution-amplifier-%28cm-3410%29)?

On the other hand, I just thought of something I hadn't even considered before. I have a Channel Plus 3025 that I don't use anymore because we no longer use the analog insertions. I had always used it along with analog cable, but it's just been collecting dust for the last 6-7 years. I see that it takes a 40 MHz to 1 GHz RF signal and handles the UHF 14-64 tuning range (in addition to the CATV 65-125 range I used to use). It has two "local" (within 35 feet) outputs and three "distant" (within 150 feet) outputs, which I'm guessing involves some amplification. Is there any reason this CP 3025 wouldn't work as a distribution amplifier that I could split my antenna signal with?
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post #18 of 23 Old 12-30-2012, 05:25 PM
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Quote:
Originally Posted by tluxon View Post

I had assumed that meant all three outputs were balanced and had an equal loss.
That's a reasonable assumption.
Quote:
...would it be a reasonable gamble to try a simple and fairly conservative in-line amplification of about 10-15 dB in front of the 3-way splitter?
That is certainly what I would try (but I'm not an RF engineer).

In your first post you stated reception was initially okay. Then you replaced a splitter with X loss with another splitter of X+Y loss.
That's the exact scenario that is described in the first response you got:
Quote:
Originally Posted by ProjectSHO89 View Post

In other words, you can keep right on splitting and running cable right up to the point where it fails.
But after that first response, seems like everybody (except kenglish) tried to answer your all-encompassing title question, rather than focus on the specific situation. Apparently your reception situation and your tuners are right at the "digital cliff". From an old post, someone actually measured signal levels that a particular tuner required for reception:
Quote:
Originally Posted by dr1394 View Post

Also note that the difference between a watchable signal (at 49 dB of attenuation) and no signal (at 51 dB of attenuation) is only 2 dB.
IOW add just 2dB of signal loss, and you could go from viewable to nothing.
That is what ProjectSHO89 was referring to before he (and others) went on about actual/abstract power levels.
Note that 2dB may be the difference between your original splitter loss (-3.5dB) and the 3-way (-5.5dB), but that's just a coincidence.
Quote:
I have a Channel Plus 3025 ...
That seems to be for only UHF, and you do have some VHF channels. But do try it as an experiment.

Regards
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post #19 of 23 Old 12-31-2012, 10:21 AM - Thread Starter
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Quote:
Originally Posted by blue_z View Post

Quote:
Originally Posted by tluxon View Post

...I have a Channel Plus 3025...
That seems to be for only UHF, and you do have some VHF channels. But do try it as an experiment.
I put the CP3025 in place of the 3-way splitter and all the signals I checked seem to be as good or better, especially the ones I had trouble with at the end of the line.

I'm not sure if I need the VHF channels, as I'm primarily going after the digital ones, but I was hoping to bump up everything that was coming down from the antenna feed. At least now I know that boosting the signal on the UHF band was a benefit. Unfortunately, I have no idea how much boost the CP3025 gives, as the specs only say that the "local" connections can go up to 35 feet and the "distant" connections can go up to 150 feet without compromising the IR repeater functionality. So I wonder if perhaps the two "local" connections may only be boosted some 2-4 dB while the three "distant" connections could be boosted by up to 10 dB?

Is there an "optimal" signal level for most tuners? If so, I'd like to avoid boosting the antenna's signal more than necessary. If I'm replacing a 2-way splitter with a 3-way splitter, wouldn't I only need a small boost of perhaps 3-6 dB to compensate for the difference in drop?
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post #20 of 23 Old 12-31-2012, 11:48 AM
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IIRC, the 3025 passes all of the TV channels (including VHF, UHF, and CATV), with about 6 dB of gain. The analog modulators, like most all the Channel Plus units I've seen, will only make a signal on UHF OTA, and upper CATV channels (selectable), not on VHF.

I don't think there is any real "standard" for optimum levels to a tuner. If the signal is undistorted, the digital tuners can be pretty sensitive...they will actually register a signal on the meter, when it is down in the noise floor. I tested an ancient Mitsubishi once, and it worked down to about -25 dBmV, which is pretty low. The subsidized DTA boxes were required to be pretty sensitive, and to meet some other performance standards, but the non-subsidized ones were not required to meet them.

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post #21 of 23 Old 01-01-2013, 04:51 PM
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I'm using a 3025 myself, ever since I started with Dish over 11 years ago. It still works great for distributing ATSC signals as well as the NTSC modulated signals.

It's best to use this as the center piece of your distribution system.

You CAN put antennas on your owned and/or controlled property...
http://www.fcc.gov/mb/facts/otard.html

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post #22 of 23 Old 01-02-2013, 03:14 PM - Thread Starter
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Quote:
Originally Posted by kenglish View Post

IIRC, the 3025 passes all of the TV channels (including VHF, UHF, and CATV), with about 6 dB of gain. The analog modulators, like most all the Channel Plus units I've seen, will only make a signal on UHF OTA, and upper CATV channels (selectable), not on VHF.
I don't think there is any real "standard" for optimum levels to a tuner. If the signal is undistorted, the digital tuners can be pretty sensitive...they will actually register a signal on the meter, when it is down in the noise floor. I tested an ancient Mitsubishi once, and it worked down to about -25 dBmV, which is pretty low. The subsidized DTA boxes were required to be pretty sensitive, and to meet some other performance standards, but the non-subsidized ones were not required to meet them.
Would it make sense then for me to look for a distribution amplifier that boosts all the outputs about 6 dB. Any recommendations? I'm not sure I want to keep using the 3025 for such a purpose - I was really just plugging it into the line to test out the theory that boosting the signal would address my issue.
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post #23 of 23 Old 01-02-2013, 05:58 PM
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A 4-out drop amp (which is merely a standard 15dB gain drop amp with a 4-way splitter on the output) has a gain of ~7dB per port.

If you want 6dB, just use a standard 15dB gain drop and put a DC-9 on the output, terminating the OUT port and connecting your distribution to the TAP leg. 15-9=6

CIAO!

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