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On upgrading a 45+ year-old OTA distribution system in my condo

post #1 of 45
Thread Starter 
We're a 40 unit condo with built-in wiring for TV, which we'd like to upgrade to HD. Before proceeding, is this the right forum?
post #2 of 45
This is probably as good a place as any. There was a thread in this forum entitled "MATV and the Digital Transition", but the last post was in 4/2011. Many who participated in that thread participate in other, similar forums, such as here. Look that thread up and see if any of your questions were answered there, then come here and we'll see what damage we can help you with. wink.gif
Edited by egnlsn - 2/20/13 at 7:40pm
post #3 of 45
What do you have now? Analog cable/Dish system? When you say you want to upgrade to HD, are you talking OTA?

If your condo is 40 years old, most likely the wiring is not RG6, unless it was updated in recent years. Also the amps and splitters might only be rated for up to 550 Mhz, whereas it should be rated up to 1000 Mhz.

What happens if you plug in an HDTV and do a scan? Do you get anything?
post #4 of 45
Thread Starter 
Quote:
Originally Posted by egnlsn View Post

This is probably as good a place as any. There was a thread in this forum entitled "MATV and the Digital Transition", but the last post was in 4/2011. Many who participated in that thread participate in other, similar forums, such as here. Look that thread up and see if any of your questions were answered there, then come here and we'll see what damage we can help you with. wink.gif
______________
I did read through that thread, thanks, and saw some useful posts, but it mostly showed me how much I (and the vendor who 'upgraded' our system, alas) need to learn about MATV problems. More below.
post #5 of 45
Thread Starter 
Quote:
Originally Posted by mikepier View Post

What do you have now? Analog cable/Dish system? When you say you want to upgrade to HD, are you talking OTA?

If your condo is 40 years old, most likely the wiring is not RG6, unless it was updated in recent years. Also the amps and splitters might only be rated for up to 550 Mhz, whereas it should be rated up to 1000 Mhz.

What happens if you plug in an HDTV and do a scan? Do you get anything?
___________________
Our condo is served by a roof-mounted HD antenna feeding into a Tru-Spec Model TA-52 launch amplifier (Pico Macom), OTA only. The signal is fed to the condo units through a bank of '60's-era splitters and RG59U coaxial cable wired throughout the walls of the building, in vertical tiers, about 12 cable runs of about 40 feet each. A 100' length of coax runs to another distribution point with a similar splitter/cable bank, another 12 runs. Each condo unit taps the signal via unshielded wall outlets, matching the 75-ohm cable to twin-lead terminals via a simple RC network.

Although the HD signal from the antenna is strong on all local channels, and the amplifier's output is similarly good (my ATSC TV has a built in signal-strength indicator), the reception at the wall-plates ranges unpredictably from fair to bad. I realize the cable may be poor for HD, but replacing that is not being considered at this time. Also, the splitters should probably be replaced, but I'd need an opinion on how much that might help.

My main question now centers on what to do about the obsolete wall-plates, and how harmful they are to HD signals. At this time, the system is working so poorly that we have few users, and even those don't use all the outlets, but cord-cutting is becoming popular. So what to do? Thanks
Edited by gring40 - 2/21/13 at 8:49am
post #6 of 45
How many stories is the building? From the TA-52, it goes to a splitter which then feeds each of the risers in the building ? Where does the 100' run originate and terminate? Is there more than 1 building? What exactly is the layout of everything? If you could do a drawing, that would be helpful.
Edited by egnlsn - 2/21/13 at 9:16am
post #7 of 45
Thread Starter 
Good question:) I'm in process of trying to create a map of the wiring layout, but am still mystified. I had thought that the wiring was done in vertical tiers, but can't say for sure. Each condo unit has outlets in the living room and several bedrooms, but I have seen that sometimes two rooms can be served from the same cable with wallplates on opposite sides of the wall. I'm now trying to map the tier-drops (sorry about that).

Our building is four stories tall atop a parking garage, and has two laundry rooms on the top floor on the North and South ends housing a splitter bank, as follows. The roof antenna feeds the TA-52 on the South side, and the output is split in two; one feed each for the South and North sides (the latter is the 100' run). The South feed first goes to a 3-way splitter, and 1) the -4dB tap goes to a two-way splitter, and 2 cables leaving that disappear into the ceiling and 2) the two -8 dB taps go to two 4-way splitters, and 8 cables from those also disappear into the ceiling. The North side is exactly the same. (Sorry, the program I used to create the diagram is an orphan and I can't send the file.)

Hope this helps to describe the situation.
post #8 of 45
Create your drawing using Microsoft Paint and save it to your desktop as a JPEG. Then, you can easily upload it to here.
post #9 of 45
Thread Starter 
Let's try uploading it as a PDF. Antenna System.pdf 4k .pdf file
post #10 of 45
So, you have a signal level of -20dBmV coming off the antenna? Does each port of the splitters go to a unit? And somewhere in the unit is the distribution for that particular unit?

One thing that needs to be kept in mind is that there is loss through the cable itself. At 750MHz, that run from the south to the north side loses ~8dB. Hence, the levels over there are ~8dB lower than the south side. Same thing with all of the runs from the splitters to the units.

Splitters and taps are 2 different things. Your drawing indicates that all devices are splitters. There are no taps. A tap would be labeled IN, OUT, TAP with there being a number such as 6 or 9 or 12 in the part number.
Edited by egnlsn - 2/21/13 at 11:00am
post #11 of 45
Thread Starter 
Quote:
Originally Posted by egnlsn View Post

So, you have a signal level of -20dBmV coming off the antenna?

Sorry, I just meant to note that the installer put a 20 dB pad at the input of the amplifier. I have no signal strength meter. Also, my operational tests of the amp output were at the test port, specified at 20 dB down, and in addition I padded that by another 18 dB or so to to protect my TV.

Quote:
Does each port of the splitters go to a unit?

I don't know where each port goes. There are no plans for the wiring of the building. Can you suggest a process for figuring that out? Is it more common to distribute the signal by tiers, or by individual units?

Quote:
And somewhere in the unit is the distribution for that particular unit?

I've never found a distribution point in a unit; where might it be commonly located?

Quote:
One thing that needs to be kept in mind is that there is loss through the cable itself. At 750MHz, that run from the south to the north side loses ~8dB. Hence, the levels over there are ~8dB lower than the south side.

Agreed; I did figure that the signal to the North side should be boosted.

Quote:
Same thing with all of the runs from the splitters to the units.

Splitters and taps are 2 different things. Your drawing indicates that all devices are splitters. There are no taps. A tap would be labeled IN, OUT, TAP with there being a number such as 6 or 9 or 12 in the part number.

Sorry about that, I was careless with my description; they are marked as splitters, not taps.
post #12 of 45
Does the building not have cable?
post #13 of 45
Thread Starter 
Quote:
Originally Posted by BiggAW View Post

Does the building not have cable?
Sure, almost everybody has Comcast or Uverse. But there's a growing group of cord-cutters who would rather get their content either online or with OTA HD (for the local channels), and our antenna system is a Common Element that ought to work and be available.
post #14 of 45
What kind of antenna is up there now? Does it look something like this?

http://www.hdtvprimer.com/ANTENNAS/VU120.gif


Also, can you post your tvfool results? It might be something as simple as re-aiming the antenna.
post #15 of 45
The drawing accounts for 20 drops, so who knows just how it was done. Ideally, each unit would have its own drop from the main splitter. Distribution within the unit would be from a splitter in the laundry room or a utility closet. I've seen them have a splitter at the living room, with the other leg going to the bedroom(s).

Are the hallway ceilings hard ceilings, or are they drop tile? One possibility is that a cable goes from the splitter in the laundry room into the ceiling of the 1st floor, where there is a 2-way splitter -- 1 leg going up and the other leg going down. Same thing for floors 3 & 4. That could explain why there are only 20 drops accounted for.

It would be sooo helpful to you if you had a signal level meter.
post #16 of 45
Tru-Spec TA-52 User's Manual is dated 2002, so it's unknown if it has been replaced sometime in the RECENT past (you might be able to locate a date on the unit):
http://picodigital.com/product-details.php?PID=77
http://www.manualslib.com/manual/129721/Pico-Macom-Ta-52.html [Click on "Download manual"]

I wouldn't worry about the mediocre Noise Figure numbers, because the large, 20 dB attenuator on the input is reducing sensitivity by a HUGE amount in order to prevent "Overload" (desensitization on weak channels)....which is probably needed due to the extremely high 48-52 dB Gain in the Preamp (which is needed to overcome the high Loss in the RF Splitter chains). For each 1 dB of input attenuation, 3rd Order Intermod Noise Distortion (IMD) is reduced by 3 dB, hence 20 dB attenuator results in 60 dB IMD reduction (probably more than is needed). Consequently, the overall system will have a much lower sensitivity than a typical home system...hopefully it's enough to receive local stations. Note that there is ALSO a switchable 10 dB attenuator built into the TA-52 that MAY be all you need if external 20 dB attenuator is removed. [It would help if you could post the results address URL (top of browser) after entering your location into www.tvfool.com]

TA-52 Spec Sheet is rather vague re Overload Specs....they appear to be saying that input levels should be below 8 dBmV for THREE strong signals, which corresponds to 50 dBmV OUTPUT after 48 dB Gain. But they didn't specify what the corresponding IMD NOISE FLOOR would be under those conditions. TA-52 User's Manual indicates that Output Capability is 60 dBmV with -50 dB cross modulation level (3 signals)...presuming 48-52 dB Gain, that is Max INPUT level of 12-8 dBmV (-37 to -41 dBm). So strongest channels per TVFool calculated RX (dBm) levels (after add Antenna Gain and subtract Balun/Downlead Losses) only need to attenuated so that their PEAK signal levels (7 dB higher than average calculated in TVFool) does not exceed 12-8 dBmV at the TA-52's input....more or less, due to inaccuracy of TVFool predictions and normal signal fluctuations. BTW: These spec numbers are for PEAK signal levels, because that was the standard way to measure ANALOG signals....and PEAKS also cause the most visible interference to video signals...whereas DTV signal levels are measured with an AVERAGE reading meter, with PEAKS 7 dB higher.

Degradation of sensitivity due to Losses in the RG-59 coax and RF Splitters are REDUCED by the amount of (extremely high) Gain in the Preamp....so changing to RG-6 won't make much of a difference unless you have some bad cable segments. Links to more info re System Noise Figure and Overload calculations are found in my fol post:
http://www.digitalhome.ca/forum/showthread.php?p=1232174
"Post 1" is found here: http://www.digitalhome.ca/forum/showthread.php?t=42426
http://www.digitalhome.ca/forum/showthread.php?p=888368 [System NF = Chart Value + Balun/Downlead Loss]

If you have access to a Signal Level Meter, you should adjust the input attenuation to determine the "best" value that allows reception of weaker channels.....DTV signal levels are much lower than old Analog, so less should be required. The FM Trap should also be switched IN and OUT to see if the second harmonics are causing problems for Ch7-13 reception and 3rd Order IMD problems on Ch5-6. Although TV Tuner specs are hard to come by, the input level to a Tuner should probably be kept between a Max of about -15 dBm (+34 dBmV) and a Min of about -80 dBm (-31 dBmV)....a 65 dB dynamic range of signals....which is ideally an 80 dB SNR range.....if the IMD levels are sufficiently low.....

I would want to measure the signal levels for all desired channels at the output of the Preamp (the -20 dB Monitor Output may Overload the meter so you can't properly measure weak signals, so you may also need an attenuator on the Monitor Output) and also make sure that the Loss in each RF Splitter is within expected tolerance on some/all desired channels....this will identify if there are problems in the RF Splitters and/or interconnecting cables. You could then check signal levels at each drop to identify which are defective and whether nearby units are also affected. There have to be more RF Splitters, perhaps in various utility closets/rooms and/or one per unit, in order to feed each drop in that unit. If a particular unit(s) is a problem, look for a closet or attic access point in that unit....or it may be stuffed behind one of the coax outlet plates.

You might want to spring for a Professional Signal Level Meter...or a lower cost alternative:
http://www.avsforum.com/t/381623/the-official-avs-antenna-and-related-hardware-topic/15150#post_22704405

FYI: Unit Conversions:
Sip (dBm) = Siv (dBmV) - 48.75
Siv (dBuV) = Siv (dBmV) + 60
Edited by holl_ands - 2/22/13 at 12:16pm
post #17 of 45
Quote:
Originally Posted by gring40 View Post

Sure, almost everybody has Comcast or Uverse. But there's a growing group of cord-cutters who would rather get their content either online or with OTA HD (for the local channels), and our antenna system is a Common Element that ought to work and be available.

Ok, gotcha.
post #18 of 45
Thread Starter 
Quote:
Originally Posted by mikepier View Post

What kind of antenna is up there now? Does it look something like this?

http://www.hdtvprimer.com/ANTENNAS/VU120.gif

Also, can you post your tvfool results? It might be something as simple as re-aiming the antenna.

Sorry, I don't have an image of the antenna, but when I attach my ATSC TV directly to the antenna I get fine reception for all the HD local channels, and the TV's built-in signal strength indicator shows very strong signals for all. As the attached TVFool results show, all those stations broadcast from the same building about 12 miles away, and we have visual line-of-sight from our roof. I really don't think its an antenna or aiming issue, but rather a problem in our ancient (VHF era) distribution system.

Radar-All.png 70k .png file
post #19 of 45
Yeah, my money is on a distribution issue. You do need to replace all of those old (probably BT) tap-offs with taps that are used nowadays. Probably the ones that are in there now have the cable stripped, with the center conductor attached to one screw and the shield connected to another screw. Same thing on the output side. The problem is that you need to know how the cable is run in order to use the right value taps.
post #20 of 45
Thread Starter 
Quote:
Originally Posted by egnlsn View Post

The drawing accounts for 20 drops, so who knows just how it was done. Ideally, each unit would have its own drop from the main splitter. .....

I've reassessed the cables leaving the distribution banks, and come up with 26 cables leaving the two; I'm counting the four cables with a high signal level as eight drops (explanation to follow), and also see that there is an extra cable (& 2-way splitter) in the North bank. So that's 12 on the South side and 14 on the North side

I'm fairly certain that the building is wired in vertical tiers for two reasons. First, we've had several instances where disruption of a wallplate (and the coax passing through it) results in a complete loss of signal at the corresponding wallplate downstairs, and a resumption of reception when the damage was fixed. Second, I know that in my own unit, there's no correlation between the reception from the wallplate in one room and the reception in another, which I'd expect if the wiring were by unit.

There is evidence that at one resident's wallplate, the signal appears to be coming from downstairs, which could mean that for the two high-signal drops it is going down one tier of wallplates and then up another (or is split somewhere), in which case that would cover two sets of outlets.

I've about finished my survey of the outlets in the building, and see that some wallplates appear on either side of a wall, so that counts as one cable drop. Add them all up and that's 26 outlets. Now I have to figure out which is which.

Quote:
Are the hallway ceilings hard ceilings, or are they drop tile? ....... It would be sooo helpful to you if you had a signal level meter.

Excellent point; we do have dropped ceilings in the hallways, and I'm going to check that out. Where can I find an affordable signal level meter?
post #21 of 45
Good signal level meters are not that inexpensive. I know of one that does analog OTA and CATV, and Digital OTA for $419 (free shipping). You would pretty much need one that does ATSC (digital OTA) since pretty much everything is digital now. Do a search for an ST- 4000D
post #22 of 45
Thread Starter 
Quote:
Originally Posted by egnlsn View Post

Yeah, my money is on a distribution issue. You do need to replace all of those old (probably BT) tap-offs with taps that are used nowadays. Probably the ones that are in there now have the cable stripped, with the center conductor attached to one screw and the shield connected to another screw. Same thing on the output side. The problem is that you need to know how the cable is run in order to use the right value taps.

I'd hoped to replace the old wallplates for active users, but not for the rest. Attached is a picture of a plate's backside, as well as a schematic. (I still have to determine how the cable is terminated at the end of a run.) Looks to me like the signal is passed straight through (at least if you don't worry about reflections?) so maybe I'll get away with that? Or possibly I'd have to replace all the plates with drop-taps in any cable drop that had an active user?

Wallplate.JPG 110k .JPG file

Antenna wallplate.pdf 44k .pdf file
post #23 of 45
My questions would be:

(1) How good of a quality is the coax, and is it still in good shape? Is it free inside the walls, or is it stapled in place everywhere....I'd wonder how hard it would be to pull it out, with a string behind it, and pull something new and better in. Also, how much slack is available, if you have to re-terminate all those cable ends?

(2) How much ingress is there, from the OTA signals leaking in to the system? You'd need to disconnect the amplifier to see how much is leaking in.

(3) How many people will use the system, and how much of a budget do you have? Do people have satellite and Cable TV in some units, and how is that wired in?

(4) How is the amplifier set up right now? Did they need the external attenuator because of overall levels being too high, or did they try to compensate for high FM levels? Is the FM trap on or off?

(5) What is on the same or nearby buildings? Any two-way radio, cellular, etc? You might need some sort of bandpass filtering on the antenna input. Also, that might make a difference in the need for better-shielded cables, too.

The amplifier is probably fine, but the distribution system is really antiquated.
post #24 of 45
Quote:
Originally Posted by gring40 View Post

I'd hoped to replace the old wallplates for active users, but not for the rest.
That is the tap I suspected was used.

You can't just replace taps (wallplates) here and there. You're going to have to replace all of the taps in a line. Nor can you just replace taps with random value taps or splitters.

You're going to need to spend a bit of time coming up with a fairly accurate map of the system. That will involve using an ohmmeter and known value resistors to figure out just where drops go and what is fed from where. Your map also needs to include distances (as close as you can guesstimate).

Ken, he wrote that the transmitters are ~12 miles away, so that pad on the input of the amp is to prevent overload.
post #25 of 45
The TA-52 has not been updated. It was a workhorse distribution amplifier of an era gone by. I think the last change was over a decade ago, when they got rid of the seperate VHF lowband and VHF highband input ports.

The maximum output level is for three equal strength analog channels. Blonder Tongue, for example, derated its public, analog benchmark maximum output levels by 4dB for 8VSB. As a rule of thumb, I derate them by about 6dB when I design systems. There is something funky about the amplifier circuit of "TA" amplifiers that makes some of their intermodulation byproducts increase more rapidly with the increase in the number of equal strength channels than do the intermodulation byproducts of more modern amplifiers, but with off-air signals, we don't have much problem with that because the signal strengths of the additional channels are ordinarily weaker than the strengths of the three strongest. I realize that theoretically, the weaker channels will be more susceptible to any noise or intermodulation distortion, but I can tell you from experience that as long as your three or four strongest channels do not exceed any benchmark level, signals that are even 20 dB weaker usually will not get decimated by the intermodulation products.

That amplifier has a switchable FM trap in it. You need to make sure it is switched in.

It looks like your stronger signals average an ambient signal strength of about -25 to -28dBm, which converts to about 25dBmV. You then gain something by the antenna but lose some strength over the downlead length. Your system's pad was selected based on the analog broadcast signals present at the time it was put in. The lower power levels of today's digital transmitters will roughly drive that amplifier to the lower maximum output of that amp when loaded digitally. If your downlead and antenna are functional, You might have three or four more full powered UHF transmitters now than you had when that system was set up, because four VHF stations in your market are now on UHF, but that would only cost you maybe two to three dB max output. But if you are curious, each of the three inputs has a switchable 10dB pad. By the way, the switches on those switchable pads are unreliable.

Old TA-52s are notorious for having filter capacitors dry out. In the analog days, when a filter capacitor failed, you could see the big black hum bar on the screen. With digital signals you cannot. You can take the channel 3/4 output from a VCR, which commonly has a signal strength of 5 to 10 dBmV, and see how it looks on a TV. Connect your TV to the -20dB test port and put the 20 dB pad in series with it. That should bring the output of the TA-52 down to maybe 15 dBmV at full gain. If you don''t see a hum, and if your picture isn't grainy, then your amp is good.

If you want to analyze this further, you can buy a used digital signal meter on eBay for under $200.
Edited by AntAltMike - 2/26/13 at 1:02pm
post #26 of 45
Another thing I thought about several years ago, on an older system like this....

If you have a couple of old VHF modulators lying around, put them on channels like 2 or 3 and 12 or 13. Then, buy one of those Channel Plus triple or quad analog modulators....they can output about a +25 dBmV on visual carriers.
Connect them all in to a single line, using a 4-way splitter, and feed the trunk line with that. Then, you can make a "spreadsheet"-like list of all your levels at each tap, at different frequencies on low-vhf, hi-vhf, and 3 or 4 UHF's.
That detailed information could show you what is wired where, and an analyzer could show serious comb-filtering, if some channels were drastically higher or lower than others at the same tap.

Of course, an expensive RF sweep generator could do the same job wink.gif .
post #27 of 45
Thread Starter 
Quote:
Originally Posted by kenglish View Post

My questions would be:

(1) How good of a quality is the coax, and is it still in good shape? Is it free inside the walls, or is it stapled in place everywhere....I'd wonder how hard it would be to pull it out, with a string behind it, and pull something new and better in. Also, how much slack is available, if you have to re-terminate all those cable ends?

Thanks for your input. The coax looks visibly OK. feels a bit stiff. It seems to be stapled to the vertical wall studs. There seems to be a fair amount of slack for re-terminating the cable ends.

Quote:
(2) How much ingress is there, from the OTA signals leaking in to the system? You'd need to disconnect the amplifier to see how much is leaking in.

No idea, but if it's important I guess I'd have to look into it.

Quote:
(3) How many people will use the system, and how much of a budget do you have? Do people have satellite and Cable TV in some units, and how is that wired in?

Not many use it now as it works so poorly, but maybe 20% of units (8 or so). The OTA antenna system is a Common Element, so we are obliged to maintain it, but with few users the Budget is debatable. The condo is wired for satellite (unused) and cable and U*Verse, but those systems are completely independently wired.

Quote:
(4) How is the amplifier set up right now? Did they need the external attenuator because of overall levels being too high, or did they try to compensate for high FM levels? Is the FM trap on or off?

The amplifier is set up now to give excellent reception at the (padded) test port for all local channels (more details if needed). I've no idea what the tilt controls do. The FM trap is IN.

Quote:
(5) What is on the same or nearby buildings? Any two-way radio, cellular, etc? You might need some sort of bandpass filtering on the antenna input. Also, that might make a difference in the need for better-shielded cables, too.

We're in a fairly dense residential neighborhood. There are only banks of air conditioners on the roof and the antenna, not counting the unused satellite dish; nothing else is allowed. I'm not aware of any radio interference nearby.

Quote:
The amplifier is probably fine, but the distribution system is really antiquated.

Hope the amplifier is OK. We asked our building manager to find a vendor to upgrade the system for HD in 2008, and he put up and aimed the antenna, and also replaced an existing TA-52 with a new one. When we asked him back to deal with reception problems in the units he proved incompetent and untrustworthy, so I'm trying to figure out the distribution system myself.
post #28 of 45
Quote:
Originally Posted by holl_ands View Post

I wouldn't worry about the mediocre Noise Figure numbers, because the large, 20 dB attenuator on the input is reducing sensitivity by a HUGE amount in order to prevent "Overload" (desensitization on weak channels)....which is probably needed due to the extremely high 48-52 dB Gain in the Preamp (which is needed to overcome the high Loss in the RF Splitter chains).

This is a primitive MATV system which, if there is no filtering and mixing network, was only capable of roughly balancing the VHF low, VHF high and UHF band levels. If all the VHF stations were in the same direction and "full powered", then your two VHF low band channels (CBS-2 and NBC-5) came off the antenna at nearly the same level as one another, as did your two VHF high band stations (ABC-7 and indepenent/WB/CW-9), so all the "system designer" cared about was driving the amplifier to its max without causing excessive sync compression. UHF signals from one market sometimes varied a little more in strength.

Quote:
TA-52 Spec Sheet is rather vague re Overload Specs....they appear to be saying that input levels should be below 8 dBmV for THREE strong signals, which corresponds to 50 dBmV OUTPUT after 48 dB Gain.

The 8dBmV figure is the minimum input level needed to enable the amplifier to be driven to full output level. 8 dBmV in plus 52 dB gain develops 60dBmV out. Those specs for three channels are for one low band, one high band and one UHF channel.

The thermal noise floor is about - 59dBmV, so if this relatively noisy amplifier has an input of even a little under 0dBmV, it will be able to sustain an NTSC analog S/N ratio of 46dB, which is what old fashioned analog MATV system designers used to shoot for.

Most distribution amps from that era didn't even have IMD figures in their original specs. They only had a maximum output level for 5% sync compression.
Quote:
If you have access to a Signal Level Meter, you should adjust the input attenuation to determine the "best" value that allows reception of weaker channels.....DTV signal levels are much lower than old Analog, so less should be required. The FM Trap should also be switched IN and OUT to see if the second harmonics are causing problems for Ch7-13 reception and 3rd Order IMD problems on Ch5-6. Although TV Tuner specs are hard to come by, the input level to a Tuner should probably be kept between a Max of about -15 dBm (+34 dBmV) and a Min of about -80 dBm (-31 dBmV)....a 65 dB dynamic range of signals....which is ideally an 80 dB SNR range.....if the IMD levels are sufficiently low.....

The MATV system is supposed to be engineered such that all of the wall taps have roughly the same signal level. Very few multiple dwelling unit master antenna systems were "engineered" for UHF distribution. They were mostly designed for VHF, with the distribution level calculations made at channel 13, and then, as more UHF stations came into the marketplace, VHF/UHF combo amps were sometimes installed, and the residents got whatever benefit from them they could. Bigger budget multiple dwelling units used heterodyne UHF to VHF converters for their most important UHF stations.

MATV wallplates typically would output a level of about 10 to 15dBmV in an ordinary, adequate system, so the same amplifier, fully loaded with digital signals, would get you wallplate levels of a little over 0dBmV, but again, that is at channel 13. The UHF values would be crapshoots, but fortunately, the early unshielded taps were rated to 890 MHz, so if you have those, you may be better off than if you had shielded taps installed in the 1970s and 1980s, because those had roll off frequencies starting anywhere from 300 MHz to 600 MHz, which would choke the UHF at higher channel numbers.
Quote:
I would want to measure the signal levels for all desired channels at the output of the Preamp

That point is not accessible on any TA series amplifiers.

Quote:
(the -20 dB Monitor Output may Overload the meter so you can't properly measure weak signals, so you may also need an attenuator on the Monitor Output)

If the max output is 60dBmV analog, I know of no meter that would overload at 40dBmV measured at the test port.
Edited by AntAltMike - 2/25/13 at 4:58am
post #29 of 45
Upon further analysis of your TV fool table, I see that ten of those local stations have ambient signal strengths of -25 to -30dBmV, so for your seat of the pants calculations, lets say that you have a load developed from ten UHF stations with field strengths of -26dBmV. I think the TA-52 has separate amplifiers for each of the three bands. If that is the case, and if you use the rule of thumb that each doubling of the channel load derates or reduces the maximum allowable output level by 3dB, then increasing the channel load from one UHF channel to two equal strength ones reduces it by 3dB, increasing the load to four equal strength UHF channels reduces it by six dB, increasing it to eight equal strength UHF channels reduces it by 9 dB, and increasing it to ten equal strength UHF channels reduces it by about 10 dB. I will leave it up to others here to estimate the likely input level at your amplifier's input based on the gain of your antenna and coax downlead loss.
Edited by AntAltMike - 2/24/13 at 9:16am
post #30 of 45
Thread Starter 
Quote:
Originally Posted by AntAltMike View Post

The TA-52 has not been updated. It was a workhorse distribution amplifier of an era gone by. I think the last change was over a decade ago, when they got rid of the seperate VHF lowband and VHF highband input ports......

Thanks for your input. The VHF low band and high band are still on my unit, bought in 2008. My locals are on the VHF high band and also the UHF band, and it's nice to be able to set the gain separately. Are you saying that the TA-52 was a poor choice in 2008 (obsolete then?) or that you would not choose that one these days?

I realize that without a signal strength meter I can't talk your language, but instead am using the qualitative signal strength meter built into a small Toshiba set, with both a cell-type 5 bar indicator and a 0-100 scale signal strength 'meter'. The two seem to correlate with each other (and the quality of the displayed picture), and I can test the signal at the antenna, at the TA-52 test point, and downstream from that. The 'meter' also correlates (reads low) with stations that are barely or unwatchable. Might this do for me?

The most obvious unexplained thing I'm seeing is that there are two separate situations, as seen at the wallplate in a unit. The first are stations with a stable picture, and stable 'meter' reading, making either a strong or weak (pixellated) picture. The second is with stations that won't come in at all, and for those, the 'meter' reading fluctuates wildly, between very weak and fairly strong, over a span of seconds. Any thoughts on that?
Edited by gring40 - 2/25/13 at 10:30am
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