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Old 30-Nov-2013, 5:49 PM   #1
Don_G
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Elbert County Colorado, two questions

I'm trying to figure out the simplest setup I can use to receive all of the channels along the 300 and 200 degree radials in the linked report.

My house is on a hill and I can get the UHF DTV channels down to 21 dB NM with any of three simple near-TV antennas. Everything I want is true LOS.

I cannot get my set to receive any VHF channels, off of either of two rabbit-ears, and I'd particularly like to get Ch 7 and Ch 9 on the 300 degree radial. Since the link margins are so high, I suspect that my TV might not even attempt to get DTV on those older channels - I cannot find any info to prove this one way or another. I seem to remember the original DTV plan was to move all channels to UHF. (???) Can anyone confirm that a Sony Bravia KDL-26M4000 can demodulate the digital signals in VHF?


At any rate, I'd like to get a setup in the attic (we get tremendous wind and ice storms here on the prairie) that gets reliable signals in all weathers. If possible, I'd like to get UHF from both Colorado Springs and Denver - a 100 degree spread. I'd also like to get VHF down to channel 7 on the 300 degree radial (Denver.)

My attic space is somewhat limited due to vaulted ceilings, but I think I can fit two 8-bay UHF antennas, and surely two 4-bay antennas.

Is this the cheapest setup for my UHF goals? Do I need an active coupler for these two antennas? Should I use two LNAs and a standard coupler? How best do I couple them and how far apart do they need to be?

I guess I'd need a third antenna for VHF on the 300 degree radial. Those noise margins are 50 dB, so it should not take much. How do I couple that in?

Thanks for your help.

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Old 30-Nov-2013, 9:15 PM   #2
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One antenna in the attic is not likely to cover a 100° arc reliably. Combining two UHF antennas (or two VHF antennas) requires filters, passive or active to prevent interference between the antennas. One antenna will receive a higher quality version of a given signal, the signal from the other antenna will act as interference if mixed together with the first.

I'd mount an RCA ANT-751 or Antennas Direct C2-V on my roof, using a high quality tripod and 5' mast. Bring on the wind and ice. A wet snow load on the roof would make for very poor reception if the antenna was stuck in the attic.

For reception from the south, I'd go big... A Winegard HD7698P and a decent preamp such as the RCA TVPRAMP1R or Channel Master CM-7778. Rather than trying to combine the south antenna with the west antenna, I'd opt for a separate tuner. http://forum.tvfool.com/showthread.php?t=2882


Per https://docs.sony.com/release/KDL26M4000.pdf pp. 42, your TV has an ATSC tuner and it covers real CH-2 through 69. An indoor antenna is subject to the interference produced by equipment in your home. That interference usually impacts the VHF band more than the UHF band. At least consider testing reception outdoors.
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Last edited by GroundUrMast; 30-Nov-2013 at 9:24 PM. Reason: Sony specs
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Old 2-Dec-2013, 3:11 AM   #3
Don_G
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Thanks, GUM,

I'm not used to reading TV specs. I had that doc, but could not reliably interpret it.

One drawback is that I cannot manually tune the TV to a digital channel. If it cannot find it in an automatic search, the channel effectively does not exist.

I figured since the two main radials I want are separated by much more than twice the 30 degree UHF 4-bay beamwidth, that the two antennas (one at 200 degres and one at 300) would sum together OK. Is there something special about the modulation that makes this problematic?

I think a 10 ft antenna would need replaced 3x a year here, so the 7698 is out of consideration for me. A smaller roof mount antenna might survive. Since I get many CoSprngs channels with an in-room antenna I don't think I need heavy metal. Your comments on snow load are well taken, but that is a very rare condition here. The wind blows the snow off the roof except right in the valleys.

In my work I'm used to seeing full specs on devices, so I'm mystified by the missing info on the combiners and couplers for TV. Here's what I typically think of for a typical power divider/combiner. Since I'm not interested in spending $130 for the coupler in this project, this info is moot. I cannot find any info on the port isolation for any of the cheaper TV combiner/splitters.

I guess if I put an amp in line between the antennas and the combiner they would supply the isolation. What's a good, cheap low gain (12 dB) amp.
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Old 2-Dec-2013, 7:38 PM   #4
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An alternative to the big combination antennas such as the HD7698P and HBU-55 would be an 8-bay panel such as the Antennas Direct DB8e and a CS5.

An amplifier will not provide the filtering needed for reliable mixing of same band signals from two same band antennas. Consider, the antenna aimed south, toward Colorado Springs will do a better job receiving the the signals from that direction but it will receive some signal from the west. The signals from the west may not be reliable but are still present and would be amplified. Once added in a broadband combiner, the higher quality version of the NW antenna signals will be mixed with the low quality version from the south antenna... The broadband combiner will not block either source, just 'mash' them together. The net signal quality will be less, even if the net raw strength is higher. The bottom line is, signal quality is not simply a function of signal strength. I'd much rather have a high quality signal at a low power level than a low quality signal at a strong power level.

To use an analogy, I'd rather have a sip of clean water, than a swimming pool full that someone just pee'd in.

Still, a good distribution amplifier that tolerates strong signals without overload that has served me well is the Channel Master CM-3410.
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Last edited by GroundUrMast; 2-Dec-2013 at 7:41 PM. Reason: sp.
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Old 5-Dec-2013, 11:56 AM   #5
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Thanks again for the reply. Please don't think I'm trying to be a smart-aleck below - I know some theory but I do not have any practical experience working with these signals.

I am not familiar with the 8VSB modulation we use here in the States, so I do not know how to quantify the signal purity required against uncorrelated interference and noise.

I know my present TV was an early design so the equalizer performance is probably very much sub-par by today's standards.

I would think that a good equalizer would treat a weaker second copy of the same signal as multipath and make use of the power in both signals. If the equalizer could not resolve the delay difference then the second copy would become a definite interference. If the delay difference was too small the signals could aid or destroy the signal power before they get to the equalizer. This could be solved by changing the cable length on one of the antennas.

The relative power of the two copies of the same signal would be set by the gain of each antenna in the direction of the transmitter. For the two 8-bay designs this would be a 12-20 dB difference at this 100 degree radial spread. For a well-designed receiver I'd think that would be enough of a difference to prevent problems either way.

I have a natural aversion moving parts, which is primarily why I don't want a rotor setup in my attic. (I also hate insulation!)

Surely someone else has been dumb enough to try this.

Don
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Old 5-Dec-2013, 4:21 PM   #6
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Quote:
I would think that a good equalizer would treat a weaker second copy of the same signal as multipath and make use of the power in both signals.
It doesn't work that way. The equalizer doesn't see the individual multi-path signals as discrete entities, it only sees the sum or difference.

You'd have to design and build a true diversity receiver to do what you've suggested.
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Old 5-Dec-2013, 5:18 PM   #7
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I guess I can see that.

So back to the other question about how far down does a co-channel interferer need to be for 8VSB?

If the signals are always more than 12 dB down between the two antennas it would seem that even at the worst case phase relationship you'd still get 75% signal strength on the sum.
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Old 5-Dec-2013, 8:28 PM   #8
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Let's back up a bit (or move sideways) and focus only on the lack of VHF reception for a moment. Those would be channels 7, 9, & 12 (13.1) from Denver which your analysis shows should be quite strong, even a capable set of simple rabbit ears should pick them up. Since you can't get them and they *should* have been "easy", perhaps that needs to be investigated to see if you have a faulty tuner or some local interference that made your two previous attempts fail.

Do you have any other TV sets available that can be tested?

What specific antennas did you try indoors? Adjust the dipoles so they are horizontal, about 26-32" tip to tip, and are oriented so that they are perpendicular to the direction the signal comes from. Some cheaper indoor antennas from RCA and GE don't obey this advice...

Are you able to move the antenna further from the TV set (yeah, they can interfere with their own reception, especially on VHF) and place the antenna in front of a window that faces Denver? You may need an extension coax and an F81 coupler to do this. Make certain the window does not have a metal window screen installed. If the glass has a low-E metallic coating, open the window for testing.


Quote:
So back to the other question about how far down does a co-channel interferer need to be for 8VSB?
See section 5 of http://www.atsc.org/cms/standards/a_74-2010.pdf

For a primer on combining antennas, see http://www.hdtvprimer.com/ANTENNAS/merging.html

Explore the "Diagnostics" option in the "Channels" menu of the Sony and see what it does.

As an experiment, set Cable to "ON" and run the auto program. See if channels 7-13 come in, ignore the lack of UHF channels
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Last edited by ADTech; 5-Dec-2013 at 8:40 PM.
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Old 6-Dec-2013, 1:57 AM   #9
Don_G
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ADtech,

Nope, just the one 24" TV. ( I know, "why bother?!")

Starting with the diagnostics: This TV will not let you tune to a digital channel it has not automatically detected. So I cannot tune to 9.1 go to the diagnostics screen and tweak the antenna.

My only choice is to tune the antenna, run a several-minute auto search and see if it finds it. I tried for hours to get 7.1 or 9.1 when I lived in Aurora (20 miles closer to the Tx) and never hit one. I tried for an hour or two when I moved here in May with no joy.

I tried again tonight using your lengths and got a hit on 7.1 and can see the pic and sound when I capacitively load the antenna with my body. So the demod works OK at VHF. I can only assume that the Rx sensitivity in that band is much poorer than UHF, or that both my antennas suck. One is a TERK. The one I got a VHF connection on tonight is an APEX.

Going to diagnostics on 7.1 I see signal strength 82, can peak the SNR to 26 dB,no errors, AGC 112%. (Is that like 11 on an amp?)

I tried shortening the antenna an inch at peak angle, but the auto detect still did not see 9.1.

Thanks for the pointer to the spec. Can I take this to mean that I need more than 15.5 dB gain pattern difference on the same channel to freely combine the two UHF antennas?

I also need a VHF-hi antenna. Is there a cheaper alternative to the Comet CF-4160J for a diplexer? ( It does look like a good one, but N-type connectors don't match F81 consumer connections.)

I really appreciate your patience.

Don

Last edited by Don_G; 6-Dec-2013 at 2:25 AM. Reason: added the Comet Duplexer question.
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Old 6-Dec-2013, 2:40 AM   #10
GroundUrMast
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UHF/VHF signal combiner options:
http://www.amazon.com/Antennas-Direc.../dp/B008PBTPN4
http://www.radioshack.com/product/in...ductId=2103923
http://www.solidsignal.com/pview.asp?p=uvsj
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Old 6-Dec-2013, 4:56 AM   #11
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Attics produce Multi-Path , multi-path is what you do not want for the following recommendation.

Directional antennas receive the least amount of signal directly on the sides of the antenna.

Install 2 Channel Master , CM4228HD antennas above the Peak of the Roof.

Aim 1 CM4228HD antenna at the , South West South group of Tv stations and keep the side (edge) of the antenna to the , North West group of Tv stations.

Aim the other CM4228HD at the , North West group of Tv stations and keep the side (edge) of the antenna to the , South West South , group of Tv stations.

To further isolate the antennas ( cross talk) connect the antennas to a , Winegard CC7870 , transformer type isolation coupler combiner.

http://www.winegarddirect.com/viewit...7870)&p=CC7870

1 coax goes from the CC7870 coupler to the Tv.

Last edited by teleview; 7-Dec-2013 at 5:17 AM. Reason: Clarify information and typos.
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Old 6-Dec-2013, 6:50 PM   #12
Don_G
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Thanks for the info on the splitters and combiners.

The CC-7870 isolation combiner is particularly welcome.

I'm gonna try a DB8E. I'll point the edges of its two 4-bays 90 degrees apart as you say (205 & 295 degrees.) If necessary I'll replace the existing combiner on that with the CC-7870. I'm getting a $20 Y5-7-13 VHF antenna and a diplexer to couple the VHF in.

If that does not get me enough signal I will turn the DB8E flat and point it at CoSprngs, then get a CM4228HD to point at Denver. It may then be more problematic on what to do with VHF, since the CM4228HD has some VHF gain.

I'll stick with the attic if I can. Not much metal in my attic to cause multipath.

I'll post how it goes...

Thanks.
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Old 6-Dec-2013, 7:48 PM   #13
teleview
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+=>
------
You understand that for Low Dollars as in 3 , 4 , $500.00 or so , no perfect solution will be found , compromises are the way it is.

With channel filters and channel modulators changing a channel to another channel and then inserting the channel/s in to distribution system and equalizer s and more and dollars that are thousands , you will get closer to getting all that you want but not all.

-----------

Here are some more alternatives.

www.slingbox.com , a slingbox a tuner a antenna at the location that you want to receive channel/s , and stream the channel/s over the Internet to your , computer / Tv.

------

www.aereo.com

-------

Some Tv stations are , streaming over the Internet.
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Old 6-Dec-2013, 7:58 PM   #14
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The CC7870 is nothing more than an older design (it was around in the mid-70s) of a splitter in an unshielded plastic outdoor box. A $6 CATV Ideal splitter from the hardware store will usually do a better job. It doesn't isolate even as well as a common splitter. Save your money.

http://www.winegard.com/kbase/kb_tip...hp?tip_num=289

I tested several of them against our two port splitter a few years back and found that their insertion loss really started dropping off above 600 MHz. Port-to-port isolation was at leas 10 dB lower than was our splitter.

You still haven't solved the issue of no reliable VHF reception with your Sony. Hopefully the 5-element antenna will do the job.
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Last edited by ADTech; 6-Dec-2013 at 8:10 PM.
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Old 19-Dec-2013, 1:25 AM   #15
Don_G
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The stuff finally all came in the DB8e lagged the rest by a week or more.

ADT you were right - the CC7870 was worse in this application.

The good news is that the Y5-7-13 and DB8e with the diplexer (a blonder tongue UVSJ) did the job. I put the VHF antenna 30 ft ENE of the DB8e to minimize any crosstalk issues. Both antennas are in the attic of a ranch house, about 14 ft AGL.

No amplifiers or other tricky bits were needed.

I get all the way down to 13.4 NM on the list, which is everything I wanted and more. All channels are above 25 dB SNR on the diagnostics screen, except 9.1 which is a marginal 21-22. If I have trouble with 9.1 I'll spring for a slightly bigger VHF antenna.

I don't know why I have issues with 9.1 at 50.2 NM, when I can get KTSC-DT ch 8.1 at a NM of only 13.4. Perhaps my TV has very poor sensitivity on that one channel? I can't picture it being an over-driving problem, but I reckon it is possible. On second thought the mis-tuned rabbit ears would have precluded any overdrive issues, so I'm back to poor sensitivity at that freq. Spurs in receivers are not unheard-of.


Thanks,
Don

Last edited by Don_G; 19-Dec-2013 at 2:01 AM. Reason: added antenna height, added overdrive statements
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