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post #1 of 7 Old 07-18-2015, 06:44 PM - Thread Starter
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Antenna reception and time of day.

A long time ago, I posted here about using a unidirectional (marine) antenna in our attic.
(In College Park, MD.)

I was pretty pleased at first. I got a total of around 40 - 45 channels with good reception. But, for better or worse, we still have cable, so we didn't use it.

I recently tried hooking the antenna up to an old Tivo Series 3 DVR, and tried to record a few things. What I didn't notice enough before was that reception for each channel varies a lot by atmospheric conditions and time of day. There are literally only several channels that are usable and reliable at all times of day!

I presume that a directional rooftop antenna would do better - but we'd have to point it to the desired channel. Many DVRs (including somewhat dated Tivo Series 3) cannot point antennas, so that's no good.

It's clear to me that a good OTA DVR must have the capability to point the antenna. Or that it would have to have as many antenna inputs as you have local broadcast towers (about 6 in our area, I think), and the ability for you to choose which input to use. Or you could get really fancy, and have it point an antenna array electronically.

I'm aware that atmospheric skipping varies with atmospheric conditions and time of day. But I'm not completely clear to what extent our particular problem is that channels from different broadcast towers interfere with each other, as opposed to not being able to get the signal cleanly at all.

What have other people interested in "cutting the cord" done about this sort of problem?
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post #2 of 7 Old 07-18-2015, 08:51 PM
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Quote:
Originally Posted by MRG1 View Post
A long time ago, I posted here about using a unidirectional (marine) antenna in our attic.
(In College Park, MD.)

I was pretty pleased at first. I got a total of around 40 - 45 channels with good reception. But, for better or worse, we still have cable, so we didn't use it.

I recently tried hooking the antenna up to an old Tivo Series 3 DVR, and tried to record a few things. What I didn't notice enough before was that reception for each channel varies a lot by atmospheric conditions and time of day. There are literally only several channels that are usable and reliable at all times of day!

I presume that a directional rooftop antenna would do better - but we'd have to point it to the desired channel. Many DVRs (including somewhat dated Tivo Series 3) cannot point antennas, so that's no good.

It's clear to me that a good OTA DVR must have the capability to point the antenna. Or that it would have to have as many antenna inputs as you have local broadcast towers (about 6 in our area, I think), and the ability for you to choose which input to use. Or you could get really fancy, and have it point an antenna array electronically.

I'm aware that atmospheric skipping varies with atmospheric conditions and time of day. But I'm not completely clear to what extent our particular problem is that channels from different broadcast towers interfere with each other, as opposed to not being able to get the signal cleanly at all.

What have other people interested in "cutting the cord" done about this sort of problem?
I've been a professional antenna installer in this market for over two decades and have serviced over a hundred multiple dwelling unit complexes and done several dozen residential installations. I also reside in a single family ranch style house in Berwyn Heights where I have three fixed antennas: an 8 bay bowtie pointed at the Washington transmitters, a Winegard combo pointed at Baltimore and a small UHF antenna pointed at Annapolis for WMPT.

I cannot for the life of me get constantly reliable reception of my Washington stations at my own home even though I have my antennas mounted on my rooftop, and have also tried a Winegard PR-9022 and a Winegard HD 6894. I have a spectrum analyzer and can see no invading signals, I have line of sight transmission paths as I am on the top of a knoll and there are no highrises on my reception lines for miles, as I have precisely plotted them.

Most of the time, my Washington reception is reliable, but occasionally, I have intervals where I have break-ups on all of the Washington channels. I have not correlated those break-up intervals to any one time of day, but they do all occur together on all the Washington channels. FWIW, the reception paths of those transmitters are all within 6 degrees of one another.

I finally moved the antenna about 30 feet laterally, from the chimney on the south end of the house to a tripod closer to the north end and that significantly reduced the incidence of the Washington break-up intervals, but didn't eliminate them completely.

When this Washington DC problem occurs, the Baltimore channels are not similarly afflicted, notwithstanding the fact that the Baltimore signals are all 20 or more dB weaker than are the Washington signals.

I used to service the antenna system at Cherry Hill Park, just inside the beltway near exit 25, and back in analog days, we used to get brutal reflections off Byrd Stadium, but with analog signals, I could see the double image and visually mitigate it, but with digital signals, there really is no way to dynamically evaluate multipath interference. I don't actually know Byrd to be my problem because I did not install these antennas until after the analogs were shut off.

Last edited by AntAltMike; 07-19-2015 at 09:59 AM.
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post #3 of 7 Old 07-19-2015, 05:30 PM - Thread Starter
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Thanks for your reply!

I'm within a few miles of you. I too am at the top of a slight hill. There are some high buildings around - specifically the USDA library, and a couple office buildings - maybe 1/4 mile away - but the fact that I get so many stations at once tells me that line of site isn't an issue to those stations. I suppose the fact that the antenna is in the attic might mean I need to skip off the atmosphere, but it sounds like you did everything right, and are a professional - presumably a trained professional - in the right area of work.You say you are already doing what I assumed must work: using a directional rooftop antenna.

There has to be a simple answer... It's not like the idea of TV reception is a completely new idea. A few blocks from me are a whole bunch of houses that have broadcast and/or satellite antenna, and people I've asked say they work well.

My Antenna is a Wineguard marine omnidirectional antenna, maybe 20" in diameter, that looks roughly like this. It's old - definitely pre-HD, but everything I've read says that doesn't matter. It doesn't have gold contacts - but it's been used indoors, and isn't corroded.

So what is your analysis of your own situation - why can't you get DC reliably? Do you get Baltimore reliably? What would it take to make these things reliable? Does one, for example, need an antenna system that searches each time for the direction of the strongest signal? (I have trouble figuring out why - but humidity is pretty high; maybe that refracts the signal...)

Incidentally, I wonder if interference from afar could be an issue despite your tests. In particular, I notice that I sometimes get DC area stations (like WTOP) on my car's FM radio if I drive to upstate NY. That suggests that under the right circumstances, radio signals can travel pretty far. In that case, there are mountains in between, so skipping must occur.


I'm not willing to buy a super-expensive system that aims suitable elements, mounted on a high local tower, at each remote broadcast tower, and amplifies them separately - that would cost more than using Comcast! I'm trying to experiment on the cheap. I'd be willing to cut a few 1/4 or 1/2 wave dipole elements from antenna wire, and point them at the broadcast towers, but I'm not sure if there is a cheap way to connect them together without interfering with each other. I guess as an experiment, I could use one element at a time - but I want to know I am trying the right things. I already tried an antenna amplifier, but apparently, the signals are already high enough the AGC in the amplifier won't boost it significantly, if at all. Of course, that its a wideband amplifier, and includes the strongest channels, so that makes sense.
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post #4 of 7 Old 07-19-2015, 05:49 PM - Thread Starter
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I just talked to an electrical engineer. He claims that many stations turn down their broadcast power at night, so they don't interfere as much.

He also claims that antenna polarization is important. For example

http://www.dtvusaforum.com/dtv-hdtv-...elevision.html

says that some stations broadcast with vertical, circular, elliptical or horizontal polarization...

I'm not sure that explains reliability - my receiver says that signal strength is strong. But he thinks polarization might affect signal to noise ratio. But a disk shaped antenna like mine might be looking at one polarization.

Anyone have any ideas of how to proceed?
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post #5 of 7 Old Yesterday, 04:35 AM
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Originally Posted by MRG1 View Post
I just talked to an electrical engineer. He claims that many stations turn down their broadcast power at night, so they don't interfere as much.
There is NO truth to this statement. (unless of course he is referring to AM radio).
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post #6 of 7 Old Yesterday, 11:33 AM - Thread Starter
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How should I proceed?

I already tried moving the antenna a few times.

Incidentally, fog is extremely rare in our area, and this doesn't just occur during rain or fog.

The problem could be anything from a big truck getting in the way, to multi-path reflections (maybe from a big truck?), to something related to atmospheric humidity, to something transmitting a signal in the same frequency band. (The latter need not by design - I used to work somewhere where, for a while, all the video monitors started displaying the signals generated by one computer, instead of the computers they were connected to. Odd, considering that neither the computers nor the monitors were designed to broadcast or receive radio signals. They found the offending computer using devices designed to locate covert spy broadcasts. Incidentally, I'm not sure a spectrum analyzer, which I don't have in any event, would clearly show very short signal pules.)

I'm not sure how to proceed!

I notice that http://www.hdtvprimer.com/ANTENNAS/siting.html says that omnidirectional antennas don't work well in multi-path situations, and that such situations are common in relatively flat regions like ours.

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post #7 of 7 Old Today, 08:20 AM - Thread Starter
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OOPS!

I made a huge mistake. I didn't notice that the cable to my antenna had come loose.

Fixed it, and most of the time of day variation went away. I'm up to receiving 50 - 55 channels or so.

So sorry to have wasted your time!
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