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Old 9-Sep-2010, 2:25 AM   #1
Coogs
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Losing Reception During the Day.

I live about 115 miles to the SW of Omaha, NE. I am able to pull in all of the available channels from Omaha during the night time hours (after dark), and they come in absolutely crystal clear all night long. However, during the daytime, I lose everyone of those stations.

Virtually the same thing happens when I swing the rotor around to Topeka, KS, which is 90 miles away. I can get WIBW all day long, but the rest to the Topeka stations only at night.

I have a Channel Master 3679 antenna mounted on top of a 40 foot tower, with a Channel Master Model 7777 Titan2™ Mast Mounted Pre-Amp. Is there anything I can do to get reception from these stations during the daylight hours?

Thanks in advance.

Here is my TVFool Report... http://www.tvfool.com/?option=com_wr...a362fe3fa3a326

Last edited by Coogs; 9-Sep-2010 at 3:03 AM.
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Old 9-Sep-2010, 3:02 AM   #2
Coogs
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BTW, here is my report...

http://www.tvfool.com/?option=com_wr...a362fe3fa3a326
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Old 9-Sep-2010, 9:16 AM   #3
kb2fzq
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115/90 miles away is a crap shoot for good reception, any way you look at it....what is probably happening is a distant station(s) is interfering with those you wish to receive during the day due to troposheric ducting (google that)....I would wait until the cooler, dryer fall weather arrives and see what happens then....
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Old 9-Sep-2010, 11:28 AM   #4
John Candle
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Tv Reception

I suggest a better antenna and preamp , Winegard HD7082P antenna , Winegard AP8275 preamp on the 40 foot tower. If this does not do it then you will need to get the antenna to 65 feet. The preamp needs to be mounted just below the antenna. I went to the >Start MAPS< part of tvfool and put in different antenna heights , 65 to 75 feet are heights that the NM(dB) noise margins improve a little and the ground reflections are less. At distances of 70 + miles heat in the air blocks Tv signals and the out right strength of the sun just blasts away at the weak Tv signals. . And also the 1 and 2 edge land path obstructions do not help any.http://www.solidsignal.com . http://www.starkelectronic.com

Last edited by John Candle; 10-Sep-2010 at 3:42 AM.
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Old 10-Sep-2010, 12:41 AM   #5
mtownsend
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The day/night cycle you are seeing is caused by an effect known as atmospheric ducting. Almost all of your stations are so far away that the Earth's curvature is getting in the way, and the transmitters end up below the horizon for you.

Here's a cross-section view of KTWU as an example. In this view, transmitter is on the left, and your location is on the right.

Note that the signals can only reach you by either diffracting over the tops of hills, bouncing off the upper atmosphere (E-skip), or bending through the lower atmosphere (ducting).

Diffracted signal is the most "direct" path between the transmitter and your antenna. Due to your distance and the terrain, the diffracted signal is very weak for most of your stations. This kind of signal is usually pretty stable throughout the day.

E-skip depends on ionization effects in the upper atmosphere (e.g., might be caused by meteor showers, solar flares, and other events) that allow radio signals to "bounce" and reach places far beyond the usual coverage area of a transmitter. These kinds of events occur sporadically, but when they do occur, it can significantly increase the received signal strength at great distances.

Atmospheric ducting is caused by a temperature inversion in the lower atmosphere (warm air near the ground, cold air above it). This turns the lower atmosphere into a kind of lens or prism that causes radio waves to bend back toward the Earth (i.e., follow the curvature of the Earth) a bit. This kind of effect primarily benefits people that are roughly 60 to 90 miles away from a transmitter (far enough to be below the horizon, yet still close enough to see a noticeable increase in signal strength). The increase in signal strength can be quite strong in the right weather conditions. This effect is usually strongest in the evening/night because the upper atmosphere cools after sunset, but the ground (gathering heat all day) keeps the lower atmosphere warm.



The bottom line here is that your main signals are pretty weak because the transmitters are so far away. Your antenna setup is probably just shy of being able to pick up the main signal during the day. You are reaching for channels that are generally considered to be very hard to get ("gray" zone in your TV Fool report).

It sounds like a few of your stations are getting enough of a boost from atmospheric ducting so that you can see them during the night.

If you want to get the channels all day long, then you need to improve your antenna reception so that it no longer relies on ducting to pull in enough signal.

The CM 7777 is already a decent amp. The Winegard amps have very similar specs, so my feeling is that switching to an AP-8275 amp won't make that much of a difference.

If you want to see an improvement, you need to do one or both of the following:

1) Increase your antenna gain.

2) Lower your pre-amp noise figure.

Switching to some higher gain antennas (like the Winegard HD8200U) might give you a few dB of improvement. Using separate UHF and VHF antennas (best of each kind) might also do a little better than a "combo" antenna.

If that's still not enough, you can gang multiple (identical) antennas together for even greater gain. Expect about a 2-3 dB improvement each time you double the number of antennas you have.

The Channel Master and Winegard amps have Noise Figures of around 2.8-3.0 dB. There are some pre-amps available with Noise Figures of around 1.0 dB or less. This can improve your net signal margin by roughly 2 dB.

Hope this helps.
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Old 10-Sep-2010, 6:18 PM   #6
Tower Guy
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Quote:
Originally Posted by Coogs View Post
I am able to pull in all of the available channels from Omaha during the night time hours. Is there anything I can do to get reception from these stations during the daylight hours?
The antenna, amplifier, and tower that you have are doing very well for you. Changing anything probably won't help enough to matter.

Most of the Omaha stations are on UHF. You can consider this antenna stacking plan: http://www.hdtvprimer.com/ANTENNAS/16bay.html Note that the newer 4228 HD has been redesigned and is not a good choice, use a pair of Winegard HD8800s instead.

I tried your location with a 300' tower. The signal strengths did not increase very much. A taller tower would help you only if there were trees, barns, or silos in the way.

I agree with the comments about interference. To eliminate that would take specially stacked high band VHF Yagis. http://www.anarc.org/wtfda/stagger.pdf

The trick with stagger stacking is that it works best when designed for a single channel. For instance, you have co-channel interference on channels 8, 10, and 13. A compromise would be to optimize the stacking distance and feedline length for channel 10. Channels 8 and 13 would still work better than they do now, not not as well as 10. That would seem to apply more to the Lincoln stations and not the Omaha stations that you want to receive.

Last edited by Tower Guy; 10-Sep-2010 at 6:26 PM.
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Old 11-Sep-2010, 2:18 AM   #7
Coogs
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Thanks guys! I already get 8 (ABC) and 10 (CBS) out of Lincoln, NE 24 hours a day. And I can get 13 (CBS) out of Topeka, KS 24 hours a day as well. I also get a FOX station out of Salina, KS all day long. NBC is a different stroy. Sometimes I can get 5 out of Hastings, NE.

I'm just getting greedy I suppose, as I would like to get Omaha and Topeka on a full time basis on all stations.

For the time being, I will probably stand pat and see what happens when the weather cools all day long. If that doesn't work, I may try one of the suggestions you guys have put forth... but I am not sure which one just yet. I do know it won't be going higher, as that really isn't an option right now.

At least I understand why I am losing signal during the daylight hours. Very interesting stuff.

Thanks again,

Coogs
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Old 13-Sep-2010, 12:55 AM   #8
Coogs
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I held reception on the Omaha channels until late morning, and then partial reception until nearly 1:00 PM. I just turned back over to WOWT and at 6:45 PM it is comming in crystal clear and holding strong. In fact all Omaha channels are in and holding at just before 7:00 PM.
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