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Old 5-Mar-2015, 1:10 AM   #1
Ultra
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Getting American TV in Canada

According to this reception report the weakest American network I can receive is ABC (I don't care about Fox) w/a -13.4dB s/n ratio. Furthermore, it's a UHF station, and has a co-channel and adjacent channel warning. (I can't even get anything NBC ) Is it reasonably possible to get such a station or would I have to take pretty extreme measures? I don't think I'd want to buy expensive hardware without the option of returning it if reception is very bad. Unfortunately, I doubt many retail stores around here carry a huge variety of antennas.
BTW, I give the antenna's height as 50' because that's how high it would be above the street. Reception would be a lot worse if that's too high a measurement.
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Old 5-Mar-2015, 3:26 PM   #2
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When the predicted NM is double digit negative, I have to go with the 'extreme measures' characterization. The bright spot on your report is that there's no strong interfering stations to struggle with when aiming southward.

To seriously consider DXing for the US signals from your location, I'd expect a tower would be the single most expensive part of the system. Any hope of success would almost certainly call for mounting above local tree top height.
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Old 5-Mar-2015, 10:06 PM   #3
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Actually, I was going to mount it the chimney. Yes, I know, but it only serves a fireplace, and it seems my flue is much bigger than the chimney for some reason, so there'd be a lot of spacing between the flue and antenna.
Another question I'd have to think about is how many stations I wouldn't be able to receive if I only used an omnidirectional. I already know how much I'd save in antenna, rotor and the vulnerability of a large array to the wind in this era of climate change. How much of a s/n ratio would I need to receive a signal w/a decent omnidirectional?
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Old 5-Mar-2015, 10:15 PM   #4
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Omni directional antennas allow interfering signals from all directions, including multipath reflections. Folks with +20 dB and higher NM values often experience reception reliability problems, not due to weak signal levels, but due to the omni antenna's inability to reduce interference received.

If you go with an omni, your hope of seeing any US signals is nil. US signal reception calls for the largest, high gain antenna or combination of antennas. They need a clear view south, free of trees and obstructing structure(s). If your reception report is accurate, a clean, interference free signal with an NM of -13.4 dB in the air will need every bit of antenna gain available in the highest performance antenna available. The 17.4 dBi specified for the DB8E is theoretically enough to get you above the absolute minimum threshold.

The combination of an Antennas Direct DB8E + Antennacraft Y10713 is what I would use to try for the US signals. I'd try to have realistic expectations though.
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Last edited by GroundUrMast; 5-Mar-2015 at 10:33 PM. Reason: added DX recommendation
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Old 5-Mar-2015, 10:31 PM   #5
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Really??? Damn! I would have thought that the interference would only be a problem for the omnis with co-channel and adjacent channel problems. Or are you thinking of problems like intermod, cross-mod, harmonics, etc?
Incidentally, nearly all the stations in that report do have NM >20dB. The next weakest is a huge drop. It seems that if I did get a beam antenna, I would only get 2 more channels that I'd ever watch.
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Old 5-Mar-2015, 10:37 PM   #6
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If you opt to go after the local signals only, much more compact antennas like the RCA ANT-751R and Antennacraft HBU-33 would do quite well.
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Old 5-Mar-2015, 10:47 PM   #7
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Quote:
Originally Posted by Ultra View Post
Really??? Damn! I would have thought that the interference would only be a problem for the omnis with co-channel and adjacent channel problems. Or are you thinking of problems like intermod, cross-mod, harmonics, etc?
Incidentally, nearly all the stations in that report do have NM >20dB. The next weakest is a huge drop. It seems that if I did get a beam antenna, I would only get 2 more channels that I'd ever watch.
Multipath seems to be very common for most folks... The direct path signal is interfered with when a reflected copy of the signal arrives at the antenna out of phase with the direct path signal. An omni tends to let that undesired signal through at a higher level than a directional antenna would. As a result, the out of phase signal(s) will likely be stronger relative to the direct path version and therefor cancel to a greater degree. When the reflection point is unstable, the fluctuating multipath generated, will cause havoc for the dynamic equalizer circuits in the tuner. This is one of the main reasons trees are so problematic... They cause rapid fluctuations in the signal path that the dynamic equalizers can't track and adjust for, therefor loosing lock on the signal.

Re. intermod, cross-mod, harmonics, etc - These are usually caused by active electronic devises, not passive object in a signal path.
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Old 5-Mar-2015, 10:58 PM   #8
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Ah, ok. Does it matter that I live in a rural area? Sure, we have as much ground as anyone else, not a lot of houses, a ton of trees (which aren't near my chimney) but the nearest skyscrapers are over 30 minutes away.
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Old 5-Mar-2015, 11:04 PM   #9
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Trees are an issue, especially for weak distant signals. This is why I mentioned the possibility of needing a tower, to get the antenna above tree top level. If the signal has to pass through foliage, there will be loss not shown on your report. In the wind, even strong local signals may not be reliably received.
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Old 5-Mar-2015, 11:07 PM   #10
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I mean does the terrain and lack of infrastructure make a difference to the multipath problem?
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Old 5-Mar-2015, 11:34 PM   #11
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Quote:
Originally Posted by Ultra View Post
I mean does the terrain and lack of infrastructure make a difference to the multipath problem?
Sure... but predicting with useful precision is beyond the capability of an online service. Too much changes, too quickly, in the real world to maintain a database that could include all trees, buildings, planes, cars, trucks, etc. Nearby trees are always expected to cause problems if forced to aim through them. The lack of nearby buildings or other flat RF reflecting surfaces suggest less classic multipath issues, but natural terrain can easily provide RF reflective surfaces.

In practice, it's far more useful to anticipate the possibility and be prepared with an antenna that has directional properties appropriate for the predicted conditions, and then be willing to experiment with alternate mounting locations and heights if the need arises. (Test reception before you drill a hole in your house.)
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