Signal analysis: I'm missing something here
http://www.tvfool.com/?option=com_wr...dfaf1406db412d
I live in a deep fringe area (literally, no transmitters of any kind above 1 kW within 30 miles) and have a nice setup (stacked yagis with a CM7777 amp). When the wind is blowing the right direction, I can get 70 channels or more from as far as 150 miles away. Rock solid for everything from San Francisco, 75 miles away. Cool. But looking at the TV signal analysis page, I'm confused by some things:
Is this a common experience for rural, somewhat hilly areas? Or am I just a dolt who doesn't understand (as opposed to a dolt that does...)? |
In order to determine the advantage of stacked antennas you should add 2.5 db to the gain of a single antenna. But even then the spacing must be optimum, which can't be true on all channels at once. Next you SUBTRACT the 3 db noise figure of the 7777 preamp. The gain of the preamp can overcome the loss of the coax and splitters, but never add to the NM.
As for the low power stations, most of them are on low band VHF. Perhaps your stacked yagis are not intended to receive channels 2-6. Next, verify your location using the online maps scheme. |
Signal analysis: I'm missing something jere
Thanks so much for your reply.
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Is NM the only determinant of "viewability", or is the dBm equally important? Is NM stated in terms of a dipole reference? In that case, stacked Yagis should give you something better than10 dB extra martin, right? (Sorry for the newbie questions, but NM is a new term for me in this context.) Quote:
[/QUOTE]Next, verify your location using the online maps scheme.[/QUOTE] Did that, the system places me correctly in the terrain. But the signal analysis indicates I should be "seeing through hills" that have me in the shadows for sure. In particular, channel 3 (second item on the report) has a huge NM and PWR rating...so it should be screaming thru, right? Yes, there's an overlap of a weaker signal (sixth one down in the list), it's 30 degrees off in azimuth so nicely attenuated in the antenna's side-lobes. Similar story with channel 6, third one on the list. |
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Your report says your antenna is only 10 feet AGL; is that true? If you click on a callsign in your report, you will see a terrain profile: KNTV http://www.tvfool.com/?option=com_wr...ALLTV%26n%3d10 KTVU http://www.tvfool.com/?option=com_wr...ALLTV%26n%3d15 Here is a terrain profile for KNTV using different software. Note the curvature of the earth makes reception more difficult. http://forum.tvfool.com/attachment.p...1&d=1481497837 |
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You are on the extreme fringe for KNTV. Small changes in location can make a big difference in signal strength. Don't be misled by the implied accuracy of the Longley-Rice coverage map; the computer simulation isn't any more accurate than about the length of a football field.
http://forum.tvfool.com/attachment.p...1&d=1481507046 http://forum.tvfool.com/attachment.p...1&d=1481507046 |
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http://www.rabbitears.info/market.ph...&callsign=kqeh click on historical ownership https://www.google.com/#q=kteh KSBW http://www.rabbitears.info/market.ph...&callsign=ksbw KSBW is 161 miles away in Salinas. The only way you can receive it is during a tropospheric propagation event. http://forum.tvfool.com/attachment.p...1&d=1481510331 |
Signal analysis: I'm missing something jere
Thanks, Rabbit, for running the other simulation software, and for the clarifying explanation. Yes, my antenna is no more than 15 feet above the ground. The XYL won't allow a tower...so can't experiment that much.
So...just for fun...Channels 2 (KTVU) and 11 (KNTV) that you simulated come in rock solid on my gear. In general, the TVFool model seems pessimistic, as I get 94 (virtual) channels from as far away as 150 miles when the wind is blowing the right direction. Where I'm confused are the situations that the model indicates a huge positive NM for a station, but there's either "nothing there" or there's a 200 foot hill right next to me that doesn't show on the terrain map. For the second issue, I'm guessing there's just not enough detail in the terrain database for my particular location. But for the signal strength seeming to be misleadingly strong, let's take a super-clear example: channel 2 in Sacramento. The model indicates I should have a -2.8 dB NM...but this is for a 3 kW transmitter 76 miles away with the terrain blockages as shown?? Seriously?? Now...that signal has a 5-meter wavelength, but I don't think low-VHF bends that much. |
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K06QM is licensed as a 100 watt station with a CP to 3 KW with a completely different coverage pattern and direction. Same for K03IC. Both are owned and operated by the same entity. Quote:
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I have a little more to answer before I do CH2.
For the images I posted, I had to know your exact antenna location coordinates, which I don't have, but I think my estimate of your location is pretty close. Quote:
http://forum.tvfool.com/attachment.p...1&d=1481511288 |
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For the same coverage area, VHF-Low requires less power than VHF-High, ignoring the higher noise level on CH 2-6, which the FCC did when it calculated power allowed by a transmitter. The FCC also assumed everyone would have a receiving antenna outside, in the clear, at 30 feet AGL. Quote:
Most tuners will drop out a signal weaker than -85 dBm at its input. I recently did a tuner sensitivity comparison between a 32" Sony and a Channel Master 7003 converter box. http://www.avsforum.com/forum/186-co...erter-box.html Yes, NM is stated in terms of a dipole reference. NM 0 is at -91 dBm, but if you don't have a preamp, you must have a NM +6 dB, to allow for the 6 dB average NF of a tuner. The report assumes the dipole is outside and in the clear. You should read the FAQs here: http://www.tvfool.com/index.php?opti...ask=view&id=57 Quote:
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My wife tolerates my antenna experiments because she wanted a battery operated TV for use during a power failure. She even bought a signal level meter for me. An indoor antenna worked for an analog TV near a window, but it doesn't work for digital TV because the insulation in the outer walls has an aluminum foil vapor barrier. We are living in a Faraday Cage. I had to set up an outdoor antenna on the porch. 73, W4... ex W2... ex DL4.. |
probably what you should be using is a ch2- 51 antenna system
UHF is strictly line of sight and severly attenuated by foliage the only way you can receive UHF is by a reflection if no line of sight Path is available high vhf (7-13) frequencies will bend slightly over hills and covers better than UHF due to lower path loss and is much less affected by foliage low vhf (2-6) cover best in hilly terrain are virtually impervious to foliage path loss is very low so coverage is very good a large combo antenna like the Winegard hd8200u would likely do a much better job for you and noise figure of amplifiers is a hair splitting debate that needs to stop the fact is that your system. noise figure is set by the TV tuner which are ALOT higher than the routine 3 or so db that most preamps have it like most of these made up specs I see these days is just another of many sales gimmicks |
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The calculation of the System Noise Figure is done with the Friis Cascaded Noise Figure Formula. https://en.wikipedia.org/wiki/Noise_figure I use this calculator: http://imageevent.com/holl_ands/files/ota COMPARE System Noise Figures With and Without Preamps It's now listed as File Number 8, but might change if more files are added. http://imageevent.com/holl_ands/file...=0&w=1&s=0&z=4 Here is the calculation I did for the Noise Margin diagram in post #6: http://forum.tvfool.com/attachment.p...1&d=1486498685 The NF of the tuner doesn't matter as much when using a preamp because its noise is added AFTER the Noise Floor has been amplified, so it is buried in the amplified noise. Quote:
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If I had the option of purchasing a better OTA stand alone tuner based on specs like I always have w/ my AM-FM Stereo tuners, I certainly would.
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