TVFool Canadian Discussion - Page 4 - Canadian TV, Computing and Home Theatre Forums

Retjk · 2009-06-29, 10:37 AM

Balm,

Sorry about the delayed response, but I've been traveling and have had limited access to the Internet. I can only speculate on why the decline in signal strength is gradual. I don't know what, if any, technical background you have, but my first suspicion is that aliasing of the RF signals is involved somewhere. If I remember correctly, I think the hdtvprimer page indicates that the expected signal pattern vertically is sinusoidal, with a period somewhere around 3 feet, but that should vary with the frequency if the TV signal. At least some of the equations there involve sinusoids, and the shading in diagrams looks sinusoidal. This means, courtesy of Nyquist, that in order to see the sinusoidal shape, you must sample at least twice during the period. But practically speaking, you must sample a lot more often than that. Even four times per period is rather crude. If you sample less than twice during the period, the signal you see is aliased and falsely indicates a period greater than that of the real signal. In fact from the sampled data it is possible to think that the period is much, much longer than that of the real signal. There are equations which describe the apparent period in terms of the real one. You could try obtaining and plotting TVFool data for in one foot increments for 4-8 feet to see whether you see a higher frequency pattern, but a sampling period of even one foot is pretty poor for an actual signal with a period of about 3 feet. In case you are not familar with aliasing, the following wikipedia page gives an illustration of what is involved under "Sampling sinusoidal functions."

http://en.wikipedia.org/wiki/Aliasing

The diagram there shows how the sampled signal has an apparent period that is longer than that of the actual, higher-frequency signal. If the rate at which you sample the signal, ie. take data, is just slightly less than the period of the signal, the apparent, but false, period can be much longer than what is even shown in that diagram. It seems conceivable that this might be what you are seeing in your data taken at 3-4 foot intervals on an actual signal that has a period in the 3-foot range.

I don't know anything about the software used by TVFool, but it may even be possible that it has similar aliasing problems. If it uses a grid that is spaced farther apart than, say, every half foot, it seems conceivable that for you to plot the signals for one-foot increments could still show the gradual signal decrease (or an increase, depending where in the sinusoid the data starts), but even that might be fictitious because of aliasing in the TVFool simulation.

Then again, I suspect that the "real-world" situation may not be as simple as hdtvprimer shows. For example, since the ground surface doing the reflecting is in general not uniformly flat, I suspect that the reflected signal may actually consist of many waves that are of various strengths and phases, resulting in a much more complex signal strength pattern than is shown on the diagram on hdtvprimer. There may be a dominant pattern related to the average ground elevation, but the actual pattern may not look nearly as nice and uniform as the one shown there.

balm · 2009-06-29, 11:16 AM

Quote:

Then again, I suspect that the "real-world" situation may not be as simple as hdtvprimer shows.

I havent digested all your info, YET, but thank you.

My real-life testing so far changing positions sideways, did not make any difference in signal strengths for any frequency, trees notwithstanding.

Also, at different height positions, for the different frequencies, AND for the different sideways postions, there doesn't seem to be much change in signal strength. So yes, it is obvious both TV Fool, and HDTVprimer, are not exact predictors.

And yes, I have extensive knowledge of physics, but it is not my specialisation, nor do I have much practical experience with it, until OTA!

balm · 2009-06-30, 08:59 AM

I would like to confirm if the TVfool Canadian channels (selection: ONLY DIGITAL, post June 12, 2009), which are listed WITHOUT the termination "-DT" are actually showing the NM's, and Pwr's, for the digital station (current or eventual)?

We have several, such as CFCF-TV (CTV) which dont include the termination "-DT", but appear based on the NM's to be the digital version. Exceptionally, CIVM-DT (TQ), and CBMT-DT (CBC), DO include the termination "-DT".

gohabsgo2 · 2009-07-02, 02:10 PM

Hi,

Does anyone know how to convert lat/long numbers that are in deg,min,sec to a decimal number that can be used in TVFOOL?

Thanks,

Larry

stampeder · 2009-07-02, 02:17 PM

Yep, see Posts #96 through 98:

http://www.digitalhome.ca/forum/showthread.php?t=108468

gohabsgo2 · 2009-07-02, 03:18 PM

Thanks Stampeder

tvlurker · 2009-07-02, 09:20 PM

Quote:

Does anyone know how to convert lat/long numbers that are in deg,min,sec to a decimal number that can be used in TVFOOL?

You don't need to use long/lat. Just input the city and province into the city field. TVFool uses Google API, so it doesn't really care how the address fields parse out. Just be sure to use the amalgamated city names, and not postal addresses. For example, Google no longer accepts "Nepean, ON", it wants "Ottawa, ON". There may be similar issues with Montreal addresses.

Also, if you use the interactive map feature, you can position your receiving location exactly in the location on your house you'll be using. Sometimes, there can be a few dB difference across the apsn of a 50-foot lot. I don't know how accurate thsi is, but it's fun to play with. :-)

balm · 2009-07-02, 09:41 PM

Quote:

Also, if you use the interactive map feature, you can position your receiving location exactly in the location on your house you'll be using. Sometimes, there can be a few dB difference across the apsn of a 50-foot lot. I don't know how accurate thsi is, but it's fun to play with. :-)

yes, this is really cool to simulate what MIGHT be your ideal sitting position on the property - I did this repeatedly, and for different heights, and it helped me place my mast in a GOOD spot, I THINK! Real-life testing will tell...

i'm not sure I understand, are you saying entering just your address, or city, province yields just as accurate results as if entering the exact coordinate?

tvlurker · 2009-07-05, 01:06 AM

Quote:

i'm not sure I understand, are you saying entering just your address, or city, province yields just as accurate results as if entering the exact coordinate?

No, just that you don't have to go to the bother of calculating the coordinates, when the Google API can do a first approximation for you -- of course, the best it will do is position you on the street near your house but after that, you can fine tune the position exactly using the interactive map feature.

stampeder · 2009-07-06, 01:53 PM

This was just posted on TVFool today indicating that the FCC has started posting Low Power stations to their database in a very confusing way:

http://www.tvfool.com/index.php?opti...d=71&Itemid=59

peano · 2009-07-20, 01:03 PM

I moved the cursor in the interactive TV Fool version to my exact location. I tried may different heights. The higher I go the worse it gets.

30 ft. is about the worst and 10 feet is the best. Is that a glitch in the program?

99gecko · 2009-07-20, 02:46 PM

Maybe. It seems to be working okay for me. I tried 10', 30', and 60' (

)

CamDAB · 2009-07-20, 04:31 PM

Quote:

Originally Posted by peano

30 ft. is about the worst and 10 feet is the best. Is that a glitch in the program?

Hmmm... This is interesting....

I'm in an apartment 10 floors up... The FCC data put only two available for me, PBS (virtual 17.1) Buffalo and 23.1 (virtual) Buffalo. It said those would be weak, and at 10 ft (which I think is the parameter) above ground level, I'd say that was accurate.

They both hammer in here all the time. I'll have to try TV Fool and see what 110 feet does...

Cameron

zapperman · 2009-07-20, 05:08 PM

Quote:

Originally Posted by peano

I moved the cursor in the interactive TV Fool version to my exact location. I tried may different heights. The higher I go the worse it gets.

30 ft. is about the worst and 10 feet is the best. Is that a glitch in the program?

Peano, I get the same thing and posed this question some time ago as well to no avail. The best guess was that there was more signal bouncing around down low, reflecting off the ground, etc, but that the resulting signal *quality" was somewhat compromised because of this. The concensus was still to get it up high and away from this potential interference and use trial and error to find your sweet spot. No real exact science...

ota_canuck · 2009-07-20, 05:35 PM

tvfool is calculated on your terrain, location, distance from the broadcast source, broadcast ERP, broadcast tower height, and clear tropospheric conditions. The higher you put your antenna will definately give you a better chance of some extra distant stations, however it also increases the chance of some co-channel [a distant station on the same freq as a local channel] and adjacent channels [a strong distant channel killing a weaker local broadcast of a local channel set-backs ,... ie; a strong distant 14.1 cross-channeling a weaker local 15.1].

co-channel [a distant station on the same freq as a local channel]

adjacent channels [a strong distant adjacent channel killing a weaker local broadcast]

Co-channel and adjacent channel is more likely with multiple/ganged antennas.

Your digital tuner will not cope well with these types of broadcast interferance conditions.

2009-07-02, 02:10 PM	#49
gohabsgo2 Join Date: Jul 2008 Location: Kitchener Posts: 78	lat / long & TV Fool Hi, Does anyone know how to convert lat/long numbers that are in deg,min,sec to a decimal number that can be used in TVFOOL? Thanks, Larry

2009-07-06, 01:53 PM	#55
stampeder OTA Forum Moderator Join Date: Jan 2005 Location: North Delta, BC (96Av x 116St) Posts: 23,338	FCC Database Change affecting TVFool This was just posted on TVFool today indicating that the FCC has started posting Low Power stations to their database in a very confusing way: http://www.tvfool.com/index.php?opti...d=71&Itemid=59

2009-07-20, 01:03 PM	#56
peano Veteran Join Date: Dec 2002 Posts: 3,586	TV Fool shows better reception at lower heights? I moved the cursor in the interactive TV Fool version to my exact location. I tried may different heights. The higher I go the worse it gets. 30 ft. is about the worst and 10 feet is the best. Is that a glitch in the program?

2009-07-20, 02:46 PM	#57
99gecko Veteran Join Date: Mar 2006 Location: Markham, ON Posts: 2,524	Maybe. It seems to be working okay for me. I tried 10', 30', and 60' ()

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2009-06-29, 10:37 AM	#46
Retjk Rookie Join Date: Jan 2009 Posts: 7	Balm, Sorry about the delayed response, but I've been traveling and have had limited access to the Internet. I can only speculate on why the decline in signal strength is gradual. I don't know what, if any, technical background you have, but my first suspicion is that aliasing of the RF signals is involved somewhere. If I remember correctly, I think the hdtvprimer page indicates that the expected signal pattern vertically is sinusoidal, with a period somewhere around 3 feet, but that should vary with the frequency if the TV signal. At least some of the equations there involve sinusoids, and the shading in diagrams looks sinusoidal. This means, courtesy of Nyquist, that in order to see the sinusoidal shape, you must sample at least twice during the period. But practically speaking, you must sample a lot more often than that. Even four times per period is rather crude. If you sample less than twice during the period, the signal you see is aliased and falsely indicates a period greater than that of the real signal. In fact from the sampled data it is possible to think that the period is much, much longer than that of the real signal. There are equations which describe the apparent period in terms of the real one. You could try obtaining and plotting TVFool data for in one foot increments for 4-8 feet to see whether you see a higher frequency pattern, but a sampling period of even one foot is pretty poor for an actual signal with a period of about 3 feet. In case you are not familar with aliasing, the following wikipedia page gives an illustration of what is involved under "Sampling sinusoidal functions." http://en.wikipedia.org/wiki/Aliasing The diagram there shows how the sampled signal has an apparent period that is longer than that of the actual, higher-frequency signal. If the rate at which you sample the signal, ie. take data, is just slightly less than the period of the signal, the apparent, but false, period can be much longer than what is even shown in that diagram. It seems conceivable that this might be what you are seeing in your data taken at 3-4 foot intervals on an actual signal that has a period in the 3-foot range. I don't know anything about the software used by TVFool, but it may even be possible that it has similar aliasing problems. If it uses a grid that is spaced farther apart than, say, every half foot, it seems conceivable that for you to plot the signals for one-foot increments could still show the gradual signal decrease (or an increase, depending where in the sinusoid the data starts), but even that might be fictitious because of aliasing in the TVFool simulation. Then again, I suspect that the "real-world" situation may not be as simple as hdtvprimer shows. For example, since the ground surface doing the reflecting is in general not uniformly flat, I suspect that the reflected signal may actually consist of many waves that are of various strengths and phases, resulting in a much more complex signal strength pattern than is shown on the diagram on hdtvprimer. There may be a dominant pattern related to the average ground elevation, but the actual pattern may not look nearly as nice and uniform as the one shown there.

2009-06-30, 08:59 AM	#48
balm Veteran Join Date: Jan 2009 Location: Montreal Posts: 2,248	I would like to confirm if the TVfool Canadian channels (selection: ONLY DIGITAL, post June 12, 2009), which are listed WITHOUT the termination "-DT" are actually showing the NM's, and Pwr's, for the digital station (current or eventual)? We have several, such as CFCF-TV (CTV) which dont include the termination "-DT", but appear based on the NM's to be the digital version. Exceptionally, CIVM-DT (TQ), and CBMT-DT (CBC), DO include the termination "-DT".

2009-07-02, 02:17 PM	#50
stampeder OTA Forum Moderator Join Date: Jan 2005 Location: North Delta, BC (96Av x 116St) Posts: 23,338	Yep, see Posts #96 through 98: http://www.digitalhome.ca/forum/showthread.php?t=108468

2009-07-02, 03:18 PM	#51
gohabsgo2 Join Date: Jul 2008 Location: Kitchener Posts: 78	Thanks Stampeder

2009-07-20, 05:35 PM	#60
ota_canuck Veteran Join Date: Mar 2009 Location: Dunnville, Ontario on the Grand River, North shore Lake Erie Posts: 2,405	tvfool is calculated on your terrain, location, distance from the broadcast source, broadcast ERP, broadcast tower height, and clear tropospheric conditions. The higher you put your antenna will definately give you a better chance of some extra distant stations, however it also increases the chance of some co-channel [a distant station on the same freq as a local channel] and adjacent channels [a strong distant channel killing a weaker local broadcast of a local channel set-backs ,... ie; a strong distant 14.1 cross-channeling a weaker local 15.1]. co-channel [a distant station on the same freq as a local channel] adjacent channels [a strong distant adjacent channel killing a weaker local broadcast] Co-channel and adjacent channel is more likely with multiple/ganged antennas. Your digital tuner will not cope well with these types of broadcast interferance conditions.