quote:

Originally posted by ensigmatic:
Noise will be induced along the coax run. (The lousier and longer the coax run the more noise it will induce.) If you put the amp at the receiver end, you'll amplify all that additional noise.

not really. No noise is being added, it's just attenuation along the coax, so you are getting closer to the Minimum Detectable Signal of the TV receiver.

quote:

What an amplifier can't cure is poor signal due to signal diffraction, refraction and reflection, or due to interfering signals on or near the desired frequencies. All it'll do is amplify the garbage along with the desired signal(s).

if he had signal diffraction, refraction and reflection, and I'll add multi-path, he would have had these with the shorter run of coax too. He said it worked with the short run of coax to the same antenna. These are (mostly) linear effects, so with everything being (mostly) linear, it would have been a problem with the shorter run. So I don't think this is his issue.

quote:

Originally posted by radioman:

quote:

Originally posted by ensigmatic:
Noise will be induced along the coax run. (The lousier and longer the coax run the more noise it will induce.) If you put the amp at the receiver end, you'll amplify all that additional noise.

not really. No noise is being added, it's just attenuation along the coax, so you are getting closer to the Minimum Detectable Signal of the TV receiver.

Yes, really. All transmission paths induce noise. Coaxial cable is no exception. Coax is not 100% immune to signal incursion, and the shield, itself, is something of an antenna. (Yes, even it it's buried.)

Tell ya what: Take an RF spectrum analyzer, plug a terminator onto its input. You'll see probably nothing. (Unless there's a strong RF source nearby.) Now slap 50 or 100 feet of coax on that same input, with a terminator on the end, and see what you see.

Even putting external noise sources aside: No transmission line is perfect. Imperfections in the transmission line, itself, induces noise. (However, for the purposes of this discussion, at which end to place an amplifier, that noise is probably pretty much a wash.)

quote:

Originally posted by radioman:

quote:

Originally posted by ensigmatic:
What an amplifier can't cure is poor signal due to signal diffraction, refraction and reflection, or due to interfering signals on or near the desired frequencies. All it'll do is amplify the garbage along with the desired signal(s).

if he had signal diffraction, refraction and reflection, and I'll add multi-path, he would have had these with the shorter run of coax too.

Multipath is caused by refraction and reflection, so saying "and multipath" is a redundancy.

quote:

Originally posted by radioman:
He said it worked with the short run of coax to the same antenna.

And if you look more carefully, you'll note I was following-up to calugo, not the OP.

quote:

Originally posted by sigarmsp226:
... this question is related to the free Digital TV signals that are available. Last year I mounted an antenna in our 2nd story home attic and it picks up the local (about 40 miles away) tv stations signal GREAT...In fact we use this line when Dish goes out due to weather....Fast Forward to today...

Wife wanted a tv with the same capabilities in the under ground storm shelter ...

Btw, sigarmsp226, let me point you to a possible alternative. See: Streaming TV Component Review

Capsule summary: You hook a networked OTA TV tuner to an antenna, then use common streaming devices to stream from that to however many TVs you want.

It's more expensive than what you're doing, but, after the initial expense it's just a question of adding a streaming device to whatever TV you want to have access to the networked tuner.

Obviously, the streamers have to have access to the home LAN by either a hardwired or wireless connection.

quote:

Originally posted by ensigmatic:

quote:

Originally posted by radioman:

quote:

Originally posted by ensigmatic:
Noise will be induced along the coax run. (The lousier and longer the coax run the more noise it will induce.) If you put the amp at the receiver end, you'll amplify all that additional noise.

not really. No noise is being added, it's just attenuation along the coax, so you are getting closer to the Minimum Detectable Signal of the TV receiver.

Yes, really. All transmission paths induce noise. Coaxial cable is no exception. Coax is not 100% immune to signal incursion, and the shield, itself, is something of an antenna. (Yes, even it it's buried.)

Tell ya what: Take an RF spectrum analyzer, plug a terminator onto its input. You'll see probably nothing. (Unless there's a strong RF source nearby.) Now slap 50 or 100 feet of coax on that same input, with a terminator on the end, and see what you see.

Even putting external noise sources aside: No transmission line is perfect. Imperfections in the transmission line, itself, induces noise. (However, for the purposes of this discussion, at which end to place an amplifier, that noise is probably pretty much a wash.)

quote:

Originally posted by radioman:

quote:

Originally posted by ensigmatic:
What an amplifier can't cure is poor signal due to signal diffraction, refraction and reflection, or due to interfering signals on or near the desired frequencies. All it'll do is amplify the garbage along with the desired signal(s).

if he had signal diffraction, refraction and reflection, and I'll add multi-path, he would have had these with the shorter run of coax too.

Multipath is caused by refraction and reflection, so saying "and multipath" is a redundancy.

quote:

Originally posted by radioman:
He said it worked with the short run of coax to the same antenna.

And if you look more carefully, you'll note I was following-up to calugo, not the OP.

Well, it seems like if we were face to face, we'd have a lively discussion about all of this I love these type of discussions (if you couldn't tell), but htis may not be the place . For the purpose of helping the OP, if we're discussing Johnson Noise generated on a length of coax, we're off in the weeds I take full responsibility for going there. My bad.

But to get us back on track, it seems like a simple system link budget equation. I don't know if you saw my other post where I suggested the coax loss is simply too high given that OTA TV is commonly somewhere north of 170 MHz and commonly transmitted at 600 MHz and even higher.

ensigmatic would you have any comments about the my other post that I'm referring to? 3rd from the bottom on the first page. This is pretty much based on link budget with a starting point being some rough (very rough) idea of how strong the signal is in the first place with TVfool.

I honestly think the loss in the cable is way too much based on loss calculations of the coax. Again, link budget stuff. I don't know of a coax that would be low enough loss that's not $4 per foot or more. I think we both agree that amps are tough without being there and accounting for all the variables. It's hit or miss.

The MDS of the receiver -- we may have fallen below. (To quote Yoda)

Oh by the way, when you run the coax into the shelter, affix it so that it has a “drip loop” so that you won’t get water in your shelter.

quote:

Originally posted by radioman:
I don't know if you saw my other post where I suggested the coax loss is simply too high given that OTA TV is commonly somewhere north of 170 MHz and commonly transmitted at 600 MHz and even higher.

Nope. I saw it. 605MHz, UHF (real/RF) channel 36 [1], is it, now. Or will be in July, when the last two phases of the channel repack [2] are completed. (Save for scattered STAs [3] for laggards.)

quote:

Originally posted by radioman:
ensigmatic would you have any comments about the my other post that I'm referring to? 3rd from the bottom on the first page.

*shrug* The Belden 9248 I use is spec'd at 4.8dB/100 ft. (interpolated value) at 600Mhz. I would place the loss at 130 ft. at somewhere around 5dB. Call it 6dB with connector insertion loss. I would not regard that as a show-stopper.

I currently have about 60 ft. of that stuff running through a splitter, which induces another 3dB of loss, so I'm seeing about the same loss as what the OP would, were he using the same coax. On a good day I can pull Toledo stations in clearly, at 65 miles away with 2edge path loss [4]. (It is almost certainly that 2edge path loss that causes the trouble on bad days.)

I've thrown a 3dB attenuator on our SiliconDust HDHomeRun networked OTA tuner, just to see what would happen, and still pulled in all but our worst stations flawlessly. That includes a station 40 miles away with 1edge path loss.

My antenna is not "big aluminum." It's a moderately-sized Winegard VHF/UHF yagi [5] at 30 ft. above ground level.

quote:

Originally posted by radioman:
I honestly think the loss in the cable is way too much based on loss calculations of the coax.

I feel your calculations, or at least your conclusions, are pessimistic.

But, and it's a big "but," that is based on quality coaxial cable and a decently-performing antenna at a reasonable elevation. We've no clue what are the loss characteristics of the cable he has, or anything else.

I've been doing antenna and transmission line stuff for a good long while. Not as much, in the last 25-30 years, as I used to, but the physics haven't changed. (If they had, we'd probably have FTL [6] travel by now .) IME, the theory is a good jumping-off point. Beyond that you just have to throw it up there and see what happens.


Explanations of some of the techno-babble, above:

[1] "Real channels" are the actual "physical" channel assignments upon which TV stations operate. What you see for channels, these days, are actually "virtual" channel numbers. Sometimes "real" = "virtual." Most times not. E.g.: "Channel 7" in Detroit is actually operating on real (RF) channel 25.

[2] "Channel repack" - All the UHF stations have been "packed down" from a high RF channel of 69 to a high RF channel of 36 to free-up the spectrum above for mobile communications.

[3]"Station Temporary Authority" - temporary rules under which a station may operate. In this case: Allowing them to stay on their pre-repack frequencies while they work out the challenges of moving to their newly-assigned frequencies.

[4] "Edge path loss" means there are "edges" between point A and point B that result in additional path loss due to refraction. The number refers to how many edges.

[5] "Yagi": Google it. That's easiest.

[6] "Faster Than Light"

I would try to maintain a very short length of cable from your $45 antenna to the TV. No need to get an amplifier then. No evidence that you need it, based on your 25' test. If it is 10' to the TV from the air vent, another 15' should put your antenna somewhere outdoors. Chances are the digital signal will be of a shortwave frequency that trees don't block.

I prefer the Mohu leaf antenna, which can be thumbtacked to a wall, or a tree outdoors, and reoriented to get the most channels. Very simple. I am getting signals from far away, even indoors.

Since your shelter is below grade, and you can have the paint roller extended above grade, it would seem in a tornado that once the you know what hits the rotating metal blades, it will blow away. So, having a backup antenna near the shelter would be prudent.

quote:

I feel your calculations, or at least your conclusions, are pessimistic.

I think part of the issue is I was going by the 250' length of coax and not 130'. and I was using a perhaps worse version of Belden cable in my coax loss calculator.

quote:

the theory is a good jumping-off point. Beyond that you just have to throw it up there and see what happens.

on this I agree 100%, which makes it tough to give advice without being there and seeing the whole picture (no pun intended).

In summary, it seems his 25' of coax is ok. 250' doesn't work. And we don't really have enough info to know if the final length of 130' will work.

Do you have power to your shelter?

How will you power the tv?

quote:

Originally posted by 4MUL8R:
Chances are the digital signal will be of a shortwave frequency that trees don't block.

You've got that one backwards. Trees are very bad news for higher frequencies--particularly when they get to blowing around in the wind.

Example: The only two local TV stations of importance to us with which we had issues were at two of the highest frequencies of all our local stations. Coupled with their tower being one of the furthest away: When the wind blew they'd go all to blazes. Since they've moved down in frequency because of the repack (650MHz down to 525MHz), the wind blows like stink and they're solid as a rock. Same tower. Same height. Relatively same power levels.

quote:

Originally posted by OKCGene:
Do you have power to your shelter?

How will you power the tv?

Hi Gene - Yes Sir we have power in the shelter. It was an option provided to us when it was installed. Runs from the breaker box in my shop and was installed by a licensed electrician. If we lose power to the house we also lose power to the shop and shelter.

Mark

Keep in mind my comments are coming from an accountant, not a cable tech nor engineer. But, I’ve been screwing around with HD via OTA since we bought our 100-yr-old home and our first plasma in 2003. Our layout has some similarities to your own, but a key difference - we live within 2 miles of the broadcast towers.

I have an 8-bay antenna mounted in the attic. Approximately 80-100’ run of rg11 coax down to the splitter / distribution point in the basement. Then rg6 is used to deliver to 4-5 TV’s. In the basement, I repurposed a 4-way combiner / splitter to use to (1) split the source rg11 to the 4 rg6 runs (one of which is then split to provide a 5th) and (2) to combine the amplification coming from the power supply that I repurposed from a 1-port rf/catv amp. (I don’t have power in the attic and thus chose to insert the amplification at the distribution hub only for convenience.) One run of OTA feeds a TIVO OTA Bolt in the man cave, which then supplies a TIVO Mini in a den. The other 4 OTA runs directly connect to TV’s either as a backup to the TIVO in those two primary rooms or as the only source in less-used rooms. My OTA system is extremely stable.

Several thoughts:
My use of rg11 was lucky. It was a long run left by Charter when they were troubleshooting my buried cable. Once they determined the issue was at the telephone pole, they left the temporary rg11 lying in my yard and I used it later when installing the antenna.

Before the full digital conversion occurred and stations prioritized the digital broadcasts, my reception was difficult for some broadcasts. The local ABC affiliate’s tower was 40 miles away (same direction as the much closer towers for the other stations) and I struggled to get anything. I tried to add in a separate antenna for that signal but without success. The solution only came when the station started to use those near towers.

Also back then, some broadcasts were lower power and my reception suffered when splitting just for two rooms. The amplification made a difference, especially when I increased the splitting for more rooms.

There is always a compromise involved with an indoor-mounted antenna, even with my optimal location. I’ve had little success with the many highly-recommended, small indoor antennas over the years.

The 4-way combiner / splitter used is an Aspen product. I can’t quite recall my original intent for it but it’s worked well, as improvised, for combining amplification and splitting with minimal loss.
http://www.summitsource.com/Ea...HN-24-Kit-P8272.aspx

For the power supply for the inline amplification, I don’t use that provided with the Aspen product but instead use one from an older 1-port amplifier. My electrical outlet is 30’ from the distribution hub and the Electroline’s power supply is connected via coax which made it simpler / cleaner to connect with the Aspen.
https://www.parts-express.com/...v-amplifier--182-560

Both of the above two parts are made in China. I don’t care. They work and they’ve lasted.

All of my coax was either left or installed years ago by a Charter technician (when that service was used by myself or the prior owner) or purchased by me from a local specialty distribution. I have been resistant to spend the money & effort to replace commercial-grade rg6 (with its commercial-grade connectors) for high-end brand names.

Since your friend can perform the connections and since 150’ of decent rg6 is not expensive, go ahead and get your length cut, run and connected. (Leave the coax unstapled so that you could use it as a pull for replacement higher-grade coax if later needed.) If needed, try a simple amplifier. Then, if that doesn’t work, you might start rethinking antenna or coax grade.

Start simple.

quote:

Originally posted by FHHM213:
I have an 8-bay antenna mounted in the attic.

An "8-bay antenna" implies it's a UHF-only antenna. Eight bow-tie-looking elements in front of a screen-like material? An 8-bay antenna with VHF elements would be YUGE

quote:

Originally posted by FHHM213:
The local ABC affiliate’s tower was 40 miles away (same direction as the much closer towers for the other stations) and I struggled to get anything.

Unless that station was very low-power or behind terrain, that might have been because it was on VHF, rather than UHF? Because, if my guess about your antenna is correct, and that station was within a CEA yellow, or even red, zone, and on UHF, you should have had no problem with it with an antenna such as you describe.

quote:

Originally posted by FHHM213:
I tried to add in a separate antenna for that signal but without success.

The only time separate antennas are called for is if you want separate UHF and VHF antennas or you have stations on different bearings such that everything you want cannot be achieved on a single antenna on one bearing. (They must be properly combined or neither will work well.)

quote:

Originally posted by FHHM213:
Also back then, some broadcasts were lower power ...

By "back then" do you mean pre-digital? In the switch from analog to digital there was also a channel repack. (The latest repack is actually the third channel repack since UHF was launched back in 1952.) In that repack, the second such, station transmit power was nearly always reduced, not increased.

That second repack reduced UHF again, from RF 14-69 to RF 14-51, moved everything out of VHF-Low (RF 2-6), and most out of VHF-High (RF 7-13), into UHF (RF 14-51). If you saw sudden "apparent" power increases in that, and assuming my guess about your antenna is correct, what you really saw was improved performance from your antenna because now the stations were broadcasting in the frequency range for which it was designed.

In this latest repack, UHF has been trimmed-down from RF 14-51 to 14-36 and some stations moved back into VHF-High. (There have even been a very few stations moved back into VHF-Low.) So some people who went out and bought fancy new "digital" antennas found themselves caught by surprise when a station they used to receive well no longer worked, because it had been moved into VHF-High, and their "digital" antenna was really a UHF-only antenna.

Some station power levels, antenna heights, and radiation patterns have changed to accommodate everything being closer together, after the latest channel repack, as well.

Another unpleasant surprise some may experience, after the current repack is complete, will be when T-Mobile (mostly) begins using the 600MHz spectrum that was UHF RF channels 38-51. Nearby cell towers using that spectrum my induce interference in the higher (current) UHF RF channels, necessitating the installation of so-called "LTE filters." (N.B.: Current LTE filters cut off at 700MHz, not 600MHZ.)

This message has been edited. Last edited by: ensigmatic,

Ensigmatic,

I may not be able to respond fully to each question but:

Yes, it is an 8-bay UHF antenna. Given my “yellow” 2-mile distance from the towers, the antenna type has been somewhat insignificant for me (within the realm of traditional external antennas mounted in attic with an otherwise clear view of the towers 2 miles away). I briefly tried to add a VHF-specific antenna in the attic to get that elusive ABC signal but gave up. In those early years, there was a limit to the degree of effort I would expend for one channel given the still-evolving level of HD programming and my wife’s reluctance to cut the cord back then. Heck, for some period, I was able to use my QAM tuner to get the unscrambled ABC signal by splitting my Charter internet feed (pre switched digital).

The ABC affiliate actually was a combination of two older nearby stations producing a single broadcast over the broader Birmingham area. One used a tower in a western county, the other used a tower in a eastern county. The western tower was roughly 40 miles further west than those nearby towers of the other networks’ affiliates. I can’t recall the real channel for the western tower then; the eastern tower was using rf 9 (thus my mentioned attempt at adding a VHF antenna pointed east). The terrain here is relatively hilly, but I think my primary issue was the direction of that far western tower. In recent years, that affiliate has been broadcasting using nearby towers and I have no issues.

By “back then”, I’m referring to the period when digital broadcasts were starting to be carried by local affiliates while still maintaining the analog broadcasts on the traditional frequency. For example, local “NBC 13” had its digital channels on 52.1, 52.2, etc. which have since been moved to 13.1, etc.

You remember those days, some networks offered some programs / events in HD. But, you then had to hope the local affiliate had taken the steps needed to broadcast that digital 720p or 1080i signal and you further hoped that the affiliate wouldn’t stretch any SD content still carried on that HD channel. Eventually more commercials were produced in HD and then local newscasts were produced in HD. The main cameras used at a race event might be HD but the in-car cameras (or sideline) cameras were SD. Etc.

I was reminded of this past history when watching (via streaming) the first 2 parts of the Michael Jordan documentary on Sunday night. That old footage was as ugly as the clothes. But man, could he play!