# digital ota issues



## erh1117 (Feb 1, 2005)

This may or may not belong in this forum...

I'm getting my Denver local digital channels using via the DISH 921 and a rooftop antenna.

I'm having issues with the signal strength jumping up and down between 70 and 0 and then no picture. This happens on a variety of channels broadcasting from a variety of locations at different times of day and different dates. Sometimes all channels come in fine. Other times, I will lose Channel 2, 9, 7, or 31 (their digital channels) in this same manner.

I've had DISH replace the 921. Same result.

My antenna is a rooftop yaggi type with a combiner to a DB4 so I can get channel 7. No preamp or amp. Don't know the gain.

I'm told this could be "multipathing," but what baffles me is that things work well for a few days, then crap out again. Random times. Random channels. Random weather conditions. Also, I've tried an inline attenuator to dumb down signal strength in case one OTA was overwhelming another.

Could it be the fact that I'm connecting two antennas? Is it the combiner?

I didn't install it or the DISH and don't plan to get on the roof. Unfortunately, the guy who installed the DISH system knows less about antennas than my eight year old niece. And, who knows if the problem is reproducible when he's here anyhow.

*So, does anyone out there you know any good antenna experts here in the Denver area? * Or am I wasting my time because it is really a 921 issue due to the known crappy stability of the 921's terrestial tuner (see http://www.satelliteguys.us/showthread.php?t=3951). If so, will L213 fix it?

Given the lack of any significant DISH HD, the locals provide the bulk of my HD viewing. If I can't view them reliably or record them for fear of losing a lock on the signal, then I might as well switch to COMCAST.

Please respond to my email address [email protected]

Ed Harris


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## boylehome (Jul 16, 2004)

It could be multipath or canselation caused from the combined antennas. A connection may be at fault, or faulty shielding. My experiences with the problem you have described mostly resulted from multipath. You may want to try using just one antenna without the combiner to see if there is improvement, then switch to the other to see if there is improvement for those channels. Is there anything in the direct view of the antenna that is shifting? How close are the antennas to each other?


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## Mark Lamutt (Mar 24, 2002)

Ed, it's definitely, absolutely the combiner that's causing your problem. I wish you'd told me this in the first place. If you have to use both antennas to see Lookout and Republic, use an A-B switch instead. From where I am, I have to use A-B switches for each of my OTA tuners.


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## erh1117 (Feb 1, 2005)

Mark-

What you say makes a lot of sense. I am using a the DB4 and the combiner to pull in channel 7 (the others come in fine via Yaggi).

Lacking the technical know-how, a tall ladder, or the nerve to climb my roof, I am having someone come out this Saturday. So, when they get here and remove the combiner, what do they do?

Do they run a separate cable from the DB4 into the house and install an A-B switch between that cable and the other antenna's cable which I can then use when I want to view channel 7?

Please explain -- and if I need to buy the A-B switch, what kind do you recommend.

Also, if you and boyle are right and "it could be multipath or canselation caused from the combined antennas, what about his suggestion that a "connection may be at fault, or faulty shielding?" Is there any way to shield better?


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## Mark Lamutt (Mar 24, 2002)

The only way a combiner can work in the Denver area is if you are using 2 identical antennas, and the signals they receive are just about exactly 180 degrees apart from each other. The reason is because the signal coming from Lookout are about 400 times stronger than the signals coming from Republic downtown. 

What kind of A-B switch to get? I use the ones that Radio Shack sells. My real question for you is will you even need an A-B switch? You have your DB4 pointing towards downtown, right, to pick up KMGH? I'd be willing to bet you a six pack of your favorite adult beverage that unless you are right in between downtown and Lookout (like I am, and I don't think you are if I remember right), that you'll pick up WB and FOX from Lookout with the DB4 pointing downtown with no problems. That's what I'd try first.

If that doesn't work, then you'll need 2 antenna cables running into your house to your 921 location. Connect the 2 cables to the A-B switch, and then the output cable from the switch connects to the 921. You can even get a remote controlled switch at Radio Shack so you don't have to get up to change it.


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## erh1117 (Feb 1, 2005)

I'll certainly try the A-B switch and tinkering with antenna placement (though I'm pretty sure that I'll still need 2 antennas because the problem leading to two antennas was that the Yaggi got all except ch 7).

But I am wondering -- if it is the combiner, why are the problems not always present? Remember that this only happens sometimes. Other times, every channel comes in fine.


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## David_Levin (Apr 22, 2002)

What's a DB4?

I'm at University and C-470 and am doing fine with the Radio Shack Yakgi mounted on the roof, aimed mostly for Republic, then tweaked it a bit towards Lookout (I'm pretty high on a hill - line of sight is good).

ABC is certainly the weakest with the 921 reporting 83/85. Lookout runs in the 90's and some of the other Republic channels will report arount 100.

Definately try to avoid the A/B switch. Multipath is a very tricky beast, expecially with the very weak signals here. 

If you must repoint (or use the A/B switch), an antenna rotor is also a possibility. Either of these really mikes timers inconvenient.

I believe the combiner MIGHT be possible, if you use an elaborate selection of filters to block common frequencies from the two antennas (no single frequency can be allowed to come from both antennas).


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## erh1117 (Feb 1, 2005)

But where do I get these filters? And who would install them?

DB4 is an antenna. See this site for a picture and info -- http://www.antennasdirect.com/db4_bow.htm


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## Mark Lamutt (Mar 24, 2002)

The filters can be very expensive, and usually have to be special ordered (at least from what I've read). And in Denver, it's hard because you need to be able to receive channel 35 from downtown and channels 32 and 34 from Lookout. Most of the cheaper filters that I've seen will either block both 34 and 35 or will let both through.


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## erh1117 (Feb 1, 2005)

Obviously, two separate cables and an A-B switch avoids the signal interference issue better, but I’d like to avoid a second cable run along my house (actually, I don’t care, but my wife does). So, would this work: Diplex the signal from the two antennas on my roof and then separate them again at the basement putting an A-B switch between them in the basement? Or would that screw the signal up too?


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## David_Levin (Apr 22, 2002)

No - again, you'd be mixing signals at the same frequency - there would be no way to reseparate them.

Where are you located? Are you really sure you can't work with 1 antenna tuned for ABC (Mark owes you a 6-pack if it doesn't work)?


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## erh1117 (Feb 1, 2005)

I"m in SE Denver -- 3rd and Colorado area. I'll try re-pointing the antenna, but I'm not optimistic.


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## David_Levin (Apr 22, 2002)

Have you looked up your antenna angles at:
www.antennaweb.org

Mine come in at 297 (fox), 298 (WB), & 344 (ABC, NBC, CBS, PBS). The Yagi seems to handle that spread fine.


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## JPC (Feb 8, 2005)

erh1117 said:


> But I am wondering -- if it is the combiner, why are the problems not always present? Remember that this only happens sometimes. Other times, every channel comes in fine.


Therein lies the mystery. I'm experiencing the exact same problem with a single ChannelMaster Stealthtenna, and I'm on my 2nd 921. (The first one had the same problem.) I could be receiving multipath from reflections, but there's not much around me that could cause them. It's my understanding that trees or other structures at a greater height than the antenna and in close proximity are the most common cause.

The random nature of the signal fluctuation is what makes me lean toward the tuner in the 921 being a little flaky. There have been numerous occasions when a soft boot temporarily fixed the problem, so that almost certainly rules out antenna placement as the sole cause.

I've also tried the 6dB pad idea thinking that the signal might be too hot, but it made no improvement.

It's certainly likely that Ed's problem has a lot to do with his dual antennas, but I'd wager yet another beverage that the 921's OTA tuner is partially to blame.

I heard a rumor that L213 is going to contain a "fix" for the OTA tuner, so maybe....


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## erh1117 (Feb 1, 2005)

Thanks to everyone for all of your input. Although frustrated and confused by it all, I will try implementing what I can of it. But, lacking a ladder, courage, and a love of heights, I again re-pose my original question:

_*"So, does anyone out there you know any good antenna experts here in the Denver area?" *_

The problem is that nobody I've contacted who installs these things seems the least bit concerned or able to adjust the antenna on the roof using CEA compass points from antennaweb and nobody seems to even have a signal meter.

Also, a new question arises:
*  Any recommendations as to what antenna to use (if I replace one or both of my current ones)?*

One installer suggests a winegard ms2000 omnidirectional. Any thoughts?


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## Mark Lamutt (Mar 24, 2002)

Ed, the DB4 should be plenty of antenna from where you are. I have no idea about installers in the area - I did my own install. If the DB4 isn't enough for some reason, your looking at jumping up to the DB8 or the Channel Master 4228, both of which are 8 bay bowtie antennas, twice the size of your current DB4.


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## bbomar (Oct 18, 2004)

erh1117 said:


> The problem is that nobody I've contacted who installs these things seems the least bit concerned or able to adjust the antenna on the roof using CEA compass points from antennaweb and nobody seems to even have a signal meter.


I'm not in the Denver area but I share your lack of interest in adjusting
an antenna on the roof. My solution was to use a Channel Master
CM 9521 rotor. Where I live I can get signals from three different DMAs 
by rotating the antenna. This rotor was available at a local store for
about $60. I agree with Mark that the DB4 is probably plenty of antenna.
If you want to read more on antennas, look here:

http://www.hdtvprimer.com/ISSUES/erecting_antenna.html

The DB4 is a bow-tie with a back reflector and that is one of the best antennas you can get. It's really strong point is directionality which
will greatly reduce multipath. I agree with everyone else that you
don't combine the output of multiple antennas which is a multipath
nightmare. My approach would be, while I had an installer out, put
up the DB4 on a rotor. That means one more cable but with two antennas
you would have two cables anyway, plus the rotor cable is pretty small
and can be attached to the signal cable with black cable ties so it is
not very noticable. Once this is set up you can adjust the antenna as
much as you like from your easy chair with the rotor's infrared remote.
You may be able to find one pointing direction that works well for all channels.
If not, the rotor allows you to store preset directions which can be
selected by pushing a single key on the remote.


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## erh1117 (Feb 1, 2005)

David_Levin said:


> No - again, you'd be mixing signals at the same frequency - there would be no way to reseparate them.


Are you sure? One installer says the signals run parallel (?) and they won't interfere like with a combiner.


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## Mark Lamutt (Mar 24, 2002)

erh1117 said:


> Are you sure? One installer says the signals run parallel (?) and they won't interfere like with a combiner.


Think about it - you are talking about electrical signals at the same frequencies from 2 different sources running down a single piece of copper wire. Not possible to be "parallel". If they were at significantly different frequencies, then yes, it's possible - ie VHF and UHF, or UHF and Satellite, but not UHF and UHF.


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## Jon Spackman (Feb 7, 2005)

yeah expensive stuff to filter it right.....channel vision makes what you need, but just one part is $1000....so might try what these guys suggest..

Jon


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## erh1117 (Feb 1, 2005)

Thanks everyone for all the input. It really has helped.

Saturday I'm going the A-B route. One last question (don't hold me to that  ) -- Will I lose some signal strength via the A-B switch decrease?


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## Mark Lamutt (Mar 24, 2002)

No, you won't lose any noticible signal strength with the A-B switch. In fact, you'll most likely gain signal strength because you're currently losing 3.5dB in signal strength with the combiner. That 3.5dB equates to HALF of your signal strength, which is why I think that once you get it out of the loop, you'll be just fine with just the DB4 antenna for both downtown and Lookout (with a possible tweak in aim).

This has been an excellent dialog that hopefully will help future users out as well. I look forward to hearing the results, Ed.


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## erh1117 (Feb 1, 2005)

Update on the OTA digital local reception issues I've had...

Recall that I have suffered form a loss of all signal on different channels at different times and experienced the oscillating pattern of 0--70--0--70 which we came to conclude was multipathing due largely to the combining of two antennae into one cable.

Today, I (well actually my installer) uncombined the signals from my two antennae by removing the combiner. Then I ran cable from the 2nd antenna to the house and connected both antennae to the 921 via a Radio Shack remote controlled A/B switch located on top of the TV. So, now we have two antennae feeding the local digital OTA's off separate cables that can be toggled via the remote.

And the result......?

Well, so far so good. Granted it is sunny and clear in Denver today, but already I am optimistic. Immediately before the uncombining surgery was performed, this patient was suffering from no signal on channels PBS 6 or NBC 9 (I mean the digital equivalent of these). Last night, I had no signal on NBC 9 in the evening and none on ABC 7 in the morning.

And, pre-op the signal strength on the channels I was getting looked like this:

WB 2 72
CBS 4 95
ABC 7 80
Fox 31 87

After the surgery, I am pleased to report that immediately post-op I received all of my OTA digital locals (all but Fox 31 on the DB4 antenna and all but ABC 7 on the Yaggi). And the signal strengths increased dramatically for each:

WB 2 105 
CBS 4 103
PBS 6 111
ABC 7 97
NBC 9 123
Fox 31 95

We'll see how it looks tonight and tomorrow and in weather, but the cure seems to be taking!!!

Thanks to all who gave me their input, time, and advice. :jumpingja :joy: :dance: :goodjob:


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## Mark Lamutt (Mar 24, 2002)

Glad to hear it, Ed.  For my own future reference, who'd you have come do the work?


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## erh1117 (Feb 1, 2005)

Paul at The Denver Dish Store.


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## David_Levin (Apr 22, 2002)

Thanks for posting the update (I hate it when people never reply back).

Did Paul install the combiner in the first place? He should have know better.

Did you try and see if a repositioning of either antenna could get you all the channels? You've got great signals strengths there and could probably afford to shift the antennas a bit towards the other locations.

I assume that the DB4 is a stronger antenna, but it might also be more directional. To the Yagi might be better for your application.

The AB switch is a fine solution but will be additional hassle if/when you add a 2nd HDTV.


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## erh1117 (Feb 1, 2005)

Paul didn't install the combiner (but did install the system itself).

As for antenna positioning, I probably could move the Yaggi and/or the DB4 and try each tweaked for position to try getting all channels on one, but that would require another installer visit ($$) and more patience than I now have left. Anyhow, I don't plan on adding HDTV to another TV and by the time I ever do, maybe DISH (if I'm still with them) will carry locals OTA digitals. Meanwhile, it will be a hassle only if I want to watch HD ABC while recording HD Fox, etc.


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## David_Levin (Apr 22, 2002)

It's also big trouble for unattended timers.

If a timer fires and you don't have the right antenna selected...

Also, be VERY careful here. Weak/unstable signals is a suspected cause of zero-second-recordings. Possibly leading to hard drive wipes.

It could be a race (between snail 1 and snail 2) to see if Echostar gets digital locals or Denver goes to full power. Either will solve your problem.

Denver is not a very big market. I doubt E* will be giving us HD locals until they get themselves a phased-array satellite (e.g. SpaceWay).

Personally - I'm not sure HD LIL is worth the bandwidth. Sure, get some Nationals for those who qualify (Simon), but most us may have to live with the OTA antenna.


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## bbomar (Oct 18, 2004)

David_Levin said:


> It's also big trouble for unattended timers.
> 
> If a timer fires and you don't have the right antenna selected...
> 
> Also, be VERY careful here. Weak/unstable signals is a suspected cause of zero-second-recordings. Possibly leading to hard drive wipes.


A rotor is no better either. I've had a timer fire when the antenna was
pointed the wrong way. It's been a few months and I don't exactly
remember the consequences, but as I recall the 921 got really confused
trying to record from a signal with lots of multipath and I had to do
more than one reboot to get things back to normal.


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