OTA reception expertise requested

[Z06_Pilot]

hi folks,

I have a Radio Shack 360 degree UHF in my attic. I am running 50' of RG6 cable to a bi-directional splitter, providing the antenna reception to OTA adaptors in each of my 722k's.

I am 3.4 miles or less from the towers of my locals. all of them register 90 + consistently on my DVR power measurements.

whenever I am viewing an OTA HD channel on either 722k, I get 1 second audio dropouts every couple of minutes, regardless of the channel. this occurs during live broadcasts(and obviously on recorded material), but does not occur on my locals when viewing the satellite feed.

could this be an OTA module issue(but it happens on both of them). Do I need to mount a different style of antenna, and do a rooftop mount to eliminate this problem, even though my reception power is very high on all local OTA channels?

thanks.

 

[boba]

Your omni directional antenna probably has an amplifier built in which you don't need. Put a $5 set of rabbit ears in that attic and see what your reception looks like at 3 miles.

 

[CowboyDren]

I had this problem with this antenna. Disconnect the amp, and it should clear up.

 

[Z06_Pilot]

thanks guys, I do indeed have the amp wired in.

I will remove and see what happens.

will let you know.

thanks!

 

[JB Antennaman]

Omni directional antenna's is not the proper way to receive a UHF signal.

Some buiding materials in your homes construction makes it opaque to UHF signals.

Your best bet is to use a good small directional antenna, pointed in the right direction.

The HBU 22 or the Winegard 7694P are both good examples of a short range combo antenna.

Depending on where you live, you might have VHF signals along with your UHF signals and a UHF antenna does not pick up very well - VHF signals.

 

[CowboyDren]

JB, he's less than 4 miles from most towers, and they're spread over 110 degrees across the horizon. The omni isn't great, but it's far more practical than another option. VHF reception is not an issue, but beam width is.

Z06, you'd get better results if you could put it on a mast outside. Any chance you can put up a gable mount or a chimney mount for a 1-1/2" antenna mast? You can get what you need at Radio Shack or online, for probably $35 total. You can't use a satellite dish mast with that antenna without heavily modifying the bracket to fit a 1-5/8" mast...ask me how I know.

 

[JB Antennaman]

Omni Directional antenna's don't do much of anything well.

A persons best bet is to have a good combo antenna and point it in the wrong direction.

A omni direction antenna, because it is not directional is very susceptible to multipath.
Multipath is when you have one signal coming from more than one direction at different times because the signal is bouncing off something - being reflected and corrupting the signal.

With analog television this was also called ghosting, because the second signal would interfere with the first - original signal and you would have two pictures at the same time.

With digital, a corrupt signal is worse then no signal at all.

The way the digital tuner works, when a piece of data is missing, it looks at what has already been received. It's all 1's and 0's.

So if you had 5 0's in a row, chances are the missing piece of data is also a 0

So it can guess and try to piece together the information and keep it going.

When you have too much data corrupt, the picture freezes and the audio stops and starts.

Sometimes living too close to the transmitter is just as bad as being too far away.

At other times, if the stick is too high up in the air, it will skip over the most local viewers and will be received 20 to 40 miles away from it's target area.

That is the main reason for the power reduction of the digital transmitter. It is easier to reduce the power and not have to work it so hard to get it to broadcast locally then to increase the power and have it go where you do not intend it to go.

A directional antenna works like a balloon. When you squeeze a balloon in the middle, the ends bulge out away from the middle. The bulge is your gain.
At the same time when you make the balloon bulge, the size or area of the balloon gets smaller in the front and back.

You might hear people mention front to back ratios on a antenna.

How the front to back works is that when the antenna is pointed in the proper direction - it still receives some signals from the back of the antenna. Although in modern communications, you never rely on a front to back because you only point your antenna where you wish it to receive, it is still good to know because the backside is usually where your multipath will come from.

By putting a reflector behind the antenna and only receiving from one direction, you eliminate some of the front to back, which is the reason why a Bay antenna sometimes works well in a fringe location that is not urban.

When people remove the screen from behind a CM 4228 antenna, they actually take away the reflector - usually to try to receive two signals from two different directions without turning the antenna.

If if works, all is well and good. If it creates more problems then it solves, then the people jump on the internet - explaining that they have a problem and are looking for a solution.

The solution - which they usually do not want to hear is to put the screen back up and use a antenna rotor to properly orientate the antenna towards the strongest part of the signal.

In this op's case, he might want to turn the antenna away from the strongest part of the signal and loose some of his gain to reduce the amount of signal going to his tuner.

One other thing he might need to do is connect his antenna wire to a 5 way splitter, which would have enough loss built into the splitter to loose a significant part of the signal to reduce the amount of signal coming in.

 

[Z06_Pilot]

hey guys,

great info. here....wow.

so pulling off the amplifier got rid of the audio dropouts, but now, the receiver gives me the "signal loss" message on every channel every 10 minutes or so. I am getting 84+ signal strength on each of the OTA channels.

so, I can certainly return the 360 antenna back to Radio Shack.

sounds like I need a directional antenna mounted on the top of my house, which I was hoping to avoid(it's a pretty steeply pitched roof), but the OTA HD channels look so pristine, I think I am going to have to give it a try!

 

[CowboyDren]

I wouldn't go directional; I'd still get a 2-bay bowtie. My geographical situation isn't that different from yours, and mine works great. I don't have any VHF channels anymore, but even when I did, the analog picture on my 2-bay was VERY good.

I use an Eagle Aspen DTV2B-UHF that I paid less than $20 for shipped (SummitSource.com). It's similar to an Antennas Direct or Terrestrial Digital dB2, or a Channel Master CM-4220, or a Winegard HD-1080. They're cheap, compact, and rugged, and have a very broad beam width. If you're not inside a commercial district, it should work for you, too.

 

[Z06_Pilot]

I wouldn't go directional; I'd still get a 2-bay bowtie. My geographical situation isn't that different from yours, and mine works great. I don't have any VHF channels anymore, but even when I did, the analog picture on my 2-bay was VERY good.

I use an Eagle Aspen DTV2B-UHF that I paid less than $20 for shipped (SummitSource.com). It's similar to an Antennas Direct or Terrestrial Digital dB2, or a Channel Master CM-4220, or a Winegard HD-1080. They're cheap, compact, and rugged, and have a very broad beam width. If you're not inside a commercial district, it should work for you, too.

cool. I missunderstood the other posts. I am definitely not in a commercial district, just a residential subdivision.

one more question: how high of the roof should I go? what is the rule of thumb? I do have a couple of trees in my front yard that are above the roof line. do I have to get the bowtie above those? that's probably 10 ft. or so above my roof line...

thanks dren....

 

[CowboyDren]

Generally, higher is better, but you don't need to be more than 5' above most reflective surfaces (shingles, etc.).

In your case it may depend on how large and mature the trees are. I assume the trees are between you and the broadcast towers. In my case, I have two 50-year-old elm trees, right in the way, less than 20' from my house, and my reception is acceptable with the antenna on a 5' mast in the middle of my roof (not more than 15' total from the ground).

Gable mounts are easiest to install and ground, and also the cheapest, but they don't work on fully-hipped roofs like mine. Chimney mounts are also nice, if you have a chimney. A tripod mount with a 5' mast section is the last option to consider, and probably the hardest to ground elegantly.

You may try just putting a bowtie in your attic where the omni is currently located, point it down the middle of your transmitter cluster, and see what happens. Omnis typically have -6dB of gain, which means they're a quarter as effective as the reference dipole antenna (rabbit ears can be configured for 0dB of gain), while a 2-bay bowtie is more like +6dB, or four times as good as the reference.

 

[Z06_Pilot]

Thanks Cowboy.

I'll take the omni back to radio shack. sounds like that's just not going to be the best option, even if roof mounted.

I'll pick up a bowtie per the online spot you mentioned, and try mounting it in the attic first.

If that does not work, I'll try a gable mount.

thanks so much for the help!

 

[boba]

As I said in the second post try a cheap set of rabbit ears in the attic. You may need an F-81 SPLICE to connect the rabbit ears coax to your coax but as close as you are to the broadcaster it may be all you need.

 

[Z06_Pilot]

hi boba,

I will try that first. in fact, when I return the 360 antenna to RS today, i will get one from the and give it a try.

 

[CowboyDren]

Budget TV Antenna - RadioShack.com

If this doesn't work, none of the others will, either.

 

[boba]

Cowboy the reviews look good I hope he tries one and it works as well for him.

 

[Z06_Pilot]

hey guys,

so, I went down to Radio shack and thought I would try this:

UHF/VHF/FM Indoor Antenna With 12-Position Fine-Tuning - RadioShack.com

put it up in my attic, and it's not bad. I get consistent 100 signal strength on 4(NBC), 6(ABC), and 10(CBS). 28(FOX), is the issue. I can't seem to get any higher then 76 signal strength, and as result, I get audio dropouts and occassional video artifacts.

tried adjusting the rabbit ears higher/lower as well as the spread between them....

argh....every site on the web I check for signals tells me that an indoor antenna should pick up all of these stations easily.

this antenna is rated for 30 miles, and i have read that if used indoors you can lose 50% of an antenna's reception capability......I am only 3.3 miles away.....

starting to wonder if I just need to bite the bullet, get one of the outdoor units you guys suggested, and put it on a gable mount.

my concern is: if I am getting virtually 100% on 3 of the 4 locals I want, and they are all basically in the same direction and distance from me, will I have any better luck getting 28?

this antenna biz is definintely more art than science :-0

 

[CowboyDren]

I don't like that antenna because it's too complicated. The more complex the system, the easier it is to screw up...but try this:

Extend the rabbit ears to full length, and set them to 45* apart (not 90*), which is to say about 23* from straight up. Point the hoop towards the tower from which ch28 is broadcast; the TVFool.com report gives you the heading information. Aim it broadside, as if the hoop were a magnifying glass and the tower is an ant you're trying to observe.

Don't worry about losing some signal from the other channels, because you have a surplus of strength, but you also have this one problem area that needs direct attention. 75 on the signal meter is waaay more than enough, but the audio dropouts indicate that you're still dealing with multipath. You can also try aiming the hoop 90* off-axis, putting the ch28 tower inside a "null," which is antenna-speak for a blind spot. You can also fiddle with the tuning dials a bit, but whatever you do, do NOT amplify this antenna.

 

[boba]

Good advice Cowboy it looks like he is almost cured. From dropouts every couple minutes to one channel being bothered by multipath is a step in the right direction. Hopefully your aiming instructions will get the last bit corrected.

 

[Z06_Pilot]

thanks folks.

I went ahead a bit the bullet and bought a Winegard 1080 locally while I am waiting for my DTVb2 to arrive in the mail.

mounted it on my 10' mast on my roof where I also have some weather station equipment mounted.....working pretty good so far....