DTV Reception Issues: signal drops intermittently to '0' and other questions.

[markwooldridge]

I don't know if this kind of question would go here, or in another forum. I know this is mainly a radio board, but we do discuss TV here and whilst there's a DX/Reception board that this question might fit into as well, I think it could go here too, so if moderators if I've posted in the wrong place, shoot me.

I'm getting the TVs in our house prepped for digital. I've got them "wonderful" converter boxes, and they're on amplified indoor antennas. I can receive all broadcast networks but on two or three of the channels I get occasional "no signal" messages, or the picture freezes or pixellates and then returns to normal. It seems to be weather dependent too, some days it's not there others you can give up on watching that channel - the freezing is too bad. It's not just on one box: it's the same 3 channels, on different set top boxes and internal amplified antennas and different locations.

I'm thinking it's a multipath problem. The reason why is that when I turn on the digibox to the signal meter, it will show a strength like 50% for most of the time and then periodically it will just drop to 0% for about a second and then back to 50%, and sometimes it's yoyo-ing between 0% and 50% quite fast.

Would someone basically confirm this?

Ultimately I need to get some form of outdoor antenna system set up. I don't want a rotator... but where I live not all the signals for all networks come from one place, I effectively have them coming from the north (ion), south (cbs, fox, cw, abc, tbn), east (pbs) and west (nbc) and that's just the in-area networks. If I got four UHF antennas and one VHF (Fox will be on VHF after transition, the others are UHF and on their final channels) how would I need to rig them together? Would this just make any multipath issues worse? Would I need to get some kind of filtering in place?

If location helps, I'm East Greensboro, NC.

Thanks in advance for any help you can provide.

 

[dhett]

and they're on amplified indoor antennas

This might be your problem if you're too close to the transmitters. I live <10 miles from the transmitters in my city and amplified antennas overloaded the signal, so I got nothing. If you can switch off the amplification on your antenna, try that. Or drop $10 for a non-amplified antenna and try it.

There could be other reasons for your problem, but it might be just as simple as that.

One word of caution: I use simple rabbit ears, but sometimes have problems if the antenna isn't pointed right. Passing cars and even people walking by the TV set can cause brief dropouts. If your signals are coming from all directions, rabbit ears might not be the best option.

 

[markwooldridge]

This might be your problem if you're too close to the transmitters. I live <10 miles from the transmitters in my city and amplified antennas overloaded the signal, so I got nothing. If you can switch off the amplification on your antenna, try that. Or drop $10 for a non-amplified antenna and try it.

I thought it might be a signal overloading issue but these are actually the weaker signals. Without amplification, I don't get them at all. One of the indoor antennas has a in-line amplifier that's attached to the RF cable, the other has an adjustable option for VHF and UHF, and an ability to turn all amplification off. Turn the amplifier off, the channels that cut out periodically go away altogether, the others remain but on a weak signal.

Thanks for your response, Mark

 

[KyDXIn]

This might be your problem if you're too close to the transmitters. I live <10 miles from the transmitters in my city and amplified antennas overloaded the signal, so I got nothing. If you can switch off the amplification on your antenna, try that. Or drop $10 for a non-amplified antenna and try it.

I thought it might be a signal overloading issue but these are actually the weaker signals. Without amplification, I don't get them at all. One of the indoor antennas has a in-line amplifier that's attached to the RF cable, the other has an adjustable option for VHF and UHF, and an ability to turn all amplification off. Turn the amplifier off, the channels that cut out periodically go away altogether, the others remain but on a weak signal.

I'm within 20 miles of our local antenna farm and I have the same trouble. I'm using an amplified RCA antenna, and some days the signal is stronger than others. Cold weather and wind seems to pixilate or render the signal unwatchable. I can't unstand how wind can affect a signal when the transmitter shouldn't be affected, and my antenna is inside protected from the wind.

 

[Tom Wells]

You have airplane flutter. Where are you with respect to the nearest airport or approaches?
The speed of the flutter changes usually if it's airplane reflections.

The rabbit ears pick up from many directions and the relected signal is cancelling the desired signal.
Yagi antennas, horizontally mounted will tend to "see" only the desired signal they are aimed at, and will
reject those from off axis. I know this doesn't help you much when you have signals from all different directions,
but maybe you could have a yagi somewhere for just those channels and switch to it when needed.

 

[kenglish]

"I thought it might be a signal overloading issue but these are actually the weaker signals."

You are getting too much signal, and it overloads the preamp. Pairs of strong signals (on different channels) will mix together, creating lower-level interference byproducts on two more (different) channels, and those can often mask lower level signals. When there is entirely too much signal somewhere in the band, this can cause Cross-modulation, which brings up the noise/distortion level all across the spectrum, effectively "drowning-out" the weaker signals.

A little bit of high-quality amplification can sometimes be a good thing, but the "amplified antennas" that are being sold are often far too much gain (some claim as much as 40-50 dB). You might try a low-gain preamp (about 10 dB) from Winegard or similar manufacturer, fed by a plain old pair of rabbit ears (with the UHF loop).
Better would be an outdoor antenna.

Here's a link to the latest Charlie Rhodes column, in Broadcast Technology magazine, if you're in to technical reading:

http://www.tvtechnology.com/article/73532

He's done a lot with Inter-Modulation in past issues, this month he's talking about actual (universally destructive) cross-mod.

 

[KyDXIn]

"I thought it might be a signal overloading issue but these are actually the weaker signals."

You are getting too much signal, and it overloads the preamp. Pairs of strong signals (on different channels) will mix together, creating lower-level interference byproducts on two more (different) channels, and those can often mask lower level signals. When there is entirely too much signal somewhere in the band, this can cause Cross-modulation, which brings up the noise/distortion level all across the spectrum, effectively "drowning-out" the weaker signals.

A little bit of high-quality amplification can sometimes be a good thing, but the "amplified antennas" that are being sold are often far too much gain (some claim as much as 40-50 dB). You might try a low-gain preamp (about 10 dB) from Winegard or similar manufacturer, fed by a plain old pair of rabbit ears (with the UHF loop).
Better would be an outdoor antenna.

Here's a link to the latest Charlie Rhodes column, in Broadcast Technology magazine, if you're in to technical reading:

http://www.tvtechnology.com/article/73532

He's done a lot with Inter-Modulation in past issues, this month he's talking about actual (universally destructive) cross-mod.

I first tried unamplifed rabbit ears and received 3 stations. Then I tried an amplified antenna and doubled that amount to 6. Sometimes at night I'm able to receive the PBS stations which easily doubles that amount to 12, but I should be able to receive (in theory) 3 more stations. Guess that will have to wait until I get an outside antenna.

 

[Madmansam]

DTV and Long Distance TV Stations Question?

My question deals with Long Distance TV Stations. I have a friend who doesn't have Cable or Satellite and only has a Roof Top Antenna. On his Analog Set, He not receives the Local Sacramento TV Stations but also several Long Distance VHF TV Stations which come in Crystal Clear however he has problems receiving the Bay Area UHF TV Stations, some comes in but has a little bit of snow on the picture. When he installs the DTV Converter Box, Will he lose reception of the Bay Area TV Stations? He lives about 80-85 miles from the Bay Area and about 25 miles from Walnut Grove, The home to the Sacramento TV Stations Transmitters. Also I have COMCAST CABLE TV. Will Cable lose their reception of the Bay Area TV Stations? I don't know if they use a Tall Large Antenna to pick up the stations or use a Microwave Dish Antenna to pick them up? Thanks!!!!