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post #1 of 654 Old 04-30-2007, 08:03 PM - Thread Starter
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Several issues have been reported regarding the new experimental site at http://www.tvfool.com/ and the signal analysis tools within, so I'm starting a new thread specifically to address those issues.

First of all, thanks everyone, for all the useful feedback. Everything on the site is quite new and it certainly still has some rough spots. I'll do my best to address the issues reported here and hopefully we'll end up with something that everyone can use.

I'm mostly staying focused on the coverage map and radar plot software development, although any web related feedback is also welcome. I can forward any web-hosting related issues to the friend that is helping me host the site. BTW, he says "Thanks!" for all the encouraging comments that people have been sending in.



Recent changes:

16-Dec-2007
- Added online coverage map browsing feature.

17-May-2007
- A brief synopsis of the search criteria used in the analysis is now included on the plot. The exact addresses and coordinates are still obfuscated for privacy reasons, but there should be enough rough information (e.g., zip code) to get an approximate idea of where the analysis is focused.
- Custom titles are now possible. If you want to include a brief description or keyword to help you remember what the report is about, now you can enter your own text to be included on the report.
- Azimuths are now color coded. This should make it easier to quickly visualize which transmitters are clustered together. A color ring has been added to the outside of the radar plot to correspond with the azimuth values.

13-May-2007
- The reports now include the network affiliation of most broadcasters. This should help avoid the hassle of having to reference other sites to get the network identities for each callsign.
- Several recommeneded formatting changes have been added. The most notable are 1) decreased radar plot size, 2) ressurection of transmitter power column, 3) expansion of the transmitter details table, 4) general formatting improvements for clarity and easier reading, 5) graph limits to prevent very strong signals from drawing over the text area.


6-May-2007
- The radar plot tool has been changed to now include a graph of channel vs. signal strength. This feature is designed to show the distinction between VHF and UHF channels and hopefully make it more obvious what kind of antenna is needed to receive each channel. This is still experimental, so any feedback on this feature is greatly appreciated.
- The HTTP referrer check has been removed. This should allow the tool to work even for those people that have disabled referrer reporting in their browsers.
- All distance and height values have been changed to miles/feet.


2-May-2007
- The FCC data extraction has been changed to a less aggressive approach. The previous approach would try to pick the most up-to-date FCC records, but in many cases, this ended up picking records for "future" (not built yet) transmitters. The new approach will hopefully do a better job of picking the transmitters that are really installed and operational today. As always, this can be improved further by individual "overrides" and feedback from all of you, so if you know of any entries that need to be corrected, please let me know.
- Another category of typos in the FCC database has been detected and fixed. This caused a small number of transmitters to be seen as having zero transmit power. Those records should now show up correctly.


29-Apr-2007
- Several people have reported formatting and screen cut-off problems in Internet Explorer 6 and a few other browsers. The site's style sheets have been changed to hopefully get the formatting right on a broader range of browsers. If you were seeing problems before, you might have better results now.


23-Apr-2007
- The coverage map processing has been increasingly automated. This makes the map generation go faster and allows me to release more metros at a time. For anyone still waiting for their metro to show up, at least now your wait won't be quite so long!



Upcoming changes:

- Maybe add the option for higher resolution (larger print) reports.



Everyone has been providing great suggestions, so please keep 'em coming!



Best regards,
Andy
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post #2 of 654 Old 04-30-2007, 08:28 PM
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AWSOME!!! DOUBLE BIG THUMBS UP !!!

I have the IE 6 and much better no cut off on the right side, everything is laid out good. Tell your friend awsome job well done. It is more detailed now that the whole picture is there.



-Willie
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post #3 of 654 Old 05-01-2007, 11:30 AM
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great site!
I noticed that with Firefox and the google toolbar, my autofill would not work with your search site for putting in my address. But yours is not the only site that it does not work in.
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post #4 of 654 Old 05-01-2007, 02:12 PM
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Quote:
Originally Posted by andy.s.lee View Post

Several issues have been reported regarding the new experimental site at http://www.tvfool.com/ and the signal analysis tools within, so I'm starting a new thread specifically to address those issues.

Everyone has been providing great suggestions, so please keep 'em coming!

Best regards,
Andy

Hi Andy;

I love the new site, THANK YOU!

I'm always trying to receive things that most would say; don't bother. In some cases I'd like to see signals even weaker than those shown. My current set-up is a 4228 on a 120' tower with 3/4" 75 ohm hardline. Your software allows me to figure out what I could get if I were to put up a 10' dish.
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post #5 of 654 Old 05-01-2007, 06:49 PM
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Andy,

I thought I sent this message to your web admin last week. The TV Signal Locator address data entry screen bounces with an error if you block the referrer header:

ERROR: Invalid referer

I have this setting on my Firefox browser to keep ad tracking to a minimum. Works OK on IE (it sends the referrer header), but now I know the header info is being looked at. Can you please tell it to disregard the header info? Thanks.

Any particular reason you chose dBm for the received power level? I would think that dBuV is (field strength) is more appropriate for this application.

Background info:
- "dBm" is a power level referenced to to 50 Ohm impedance. TV applications use 75 Ohm coax. That's after the antenna transfers the received signal voltage onto the coax.
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post #6 of 654 Old 05-06-2007, 01:42 PM - Thread Starter
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Quote:
Originally Posted by GeekGirl View Post

Andy,

I thought I sent this message to your web admin last week. The TV Signal Locator address data entry screen bounces with an error if you block the referrer header:

ERROR: Invalid referer

I have this setting on my Firefox browser to keep ad tracking to a minimum. Works OK on IE (it sends the referrer header), but now I know the header info is being looked at. Can you please tell it to disregard the header info? Thanks.

Thanks for the feedback!

The invalid referrer check has been removed, so hopefully things will work for you now.

The purpose of such as check is actually to prevent abuse of the URL from third-party "unscrupulous" web hosts creating direct links into the tool interface. I will leave the check disabled unless there's a significant rise in server abuse.



Quote:


Any particular reason you chose dBm for the received power level? I would think that dBuV is (field strength) is more appropriate for this application.

Background info:
- "dBm" is a power level referenced to to 50 Ohm impedance. TV applications use 75 Ohm coax. That's after the antenna transfers the received signal voltage onto the coax.

The choice to use dBm over dBuV is mostly for ease of use. The conversion between the two is trivial, so from a processing point of view they are interchangable.

Field strength (and power flux density) is more useful when it comes to antenna and waveguide analysis/testing. It is the preferred unit for broadcast engineers and facility managers because it's the easy to measure and understand in the scope of what they're doing. Power is more useful when it comes to analyzing individual tranmitter and receiver devices (e.g., silicon devices, tuners, power amplifiers, LNAs, filters, etc.). As for propagation modeling, the units actually doesn't matter, because a dB of loss in dBuV is also a dB of loss in dBm.

Since I mostly deal with designing and testing devices (e.g., cell phones, GPS, TV, etc.) rather than the antenna systems, I find it more convenient to deal with power units. Most of the lab equipment (e.g., spectrum analyzers) and other devices that I deal with provide specifications in terms of power. With everything specified in terms of power, it's easier to estimate things like heat dissipation (for transmission paths), SNR relative to thermal noise floor (in receive paths), and device signal handling capacity.

The relationship between dBm and dBuV is
Code:
dBm = dBuV - 90 - 20*log( sqrt( impedance ) )
, so you're right that dBm does vary with impedance, but for consumer TVs, we mostly just care about the 75 ohm case (btw, there's only a 1.8 dB difference between 50 and 75 ohm systems).

In a non-engineering sense, I also think that power means more to the average person than field strength. Most of us have an instinctive feel for what it means to transmit 5 megawatts of power, but don't have a good feel for what 41 dBu means.

Best regards,
Andy
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post #7 of 654 Old 05-06-2007, 11:00 PM - Thread Starter
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OK, all the units in the radar plot tool have been changed to miles and feet. Hopefully, this will cause less confusion for everybody.

Best regards,
Andy
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post #8 of 654 Old 05-07-2007, 09:03 AM
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Wow!
RIP antennaweb (thank goodness).

When/where did this come from? Andy; do we thank you for this??

I have never done a 'bit torrent' d/l, is there another way of getting the data for Google Earth for my area?

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post #9 of 654 Old 05-07-2007, 09:43 AM
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Quote:
OK, all the units in the radar plot tool have been changed to miles and feet.

How about received antenna height?

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post #10 of 654 Old 05-07-2007, 12:22 PM - Thread Starter
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Quote:
Originally Posted by videobruce View Post

How about received antenna height?

D'OH! I forgot to change that. Thanks for catching this. It's been fixed now. I guess that's what I get for coding late at night.

Best regards,
Andy
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post #11 of 654 Old 05-07-2007, 01:29 PM - Thread Starter
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Quote:
Originally Posted by videobruce View Post

Wow!
RIP antennaweb (thank goodness).

When/where did this come from? Andy; do we thank you for this??

Yep. I originally developed my radar plot tool because I always felt that antennaweb was dumbed-down too much. Colored wedge charts give very little real information, and I'm not sure that it's helping make the consumer's life any easier. As an electrical engineer, I felt I needed more detailed information about each signal to really understand how to optimize reception and antenna selection. When I started generating plots to help answer other avs members' questions, people seemed pretty interested in the analysis tool, so I started work on making an online version available.



Quote:
Originally Posted by videobruce View Post

I have never done a 'bit torrent' d/l, is there another way of getting the data for Google Earth for my area?

I know ********** is new to a lot of people. The Google Earth files are quite large and demand for them is fairly high, so torrents were the only way I could distribute the files with reasonable speed given the limited bandwidth of my network connection. ********** is much more efficient with bandwidth utilization because it aggregates shared bandwidth from many servers simultaneously. Pieces of each file can be downloaded from multiple sources at the same time until it assembles a whole copy of the original. If many people are downloading the same file, they can also help each other because each person will download some pieces from my server and also get some pieces from other peers. This way, everybody shares a fraction of the bandwidth load and everybody ends up getting the file faster.

I am searching for better hosting facilities that have enough storage and bandwidth to allow for direct dowloads, but I don't expect anything to be ready for quite a while. The collection of files is already several gigabytes and I still have a lot of metros to add.

Given my current setup, ********** is the only viable option for now. The good news is that the latest ********** clients have become quite good. For Windows users, uTorrent is nice because it does not require any installation (it's just one executable), it's very small and efficient, and it's rich with features. Azureus runs on any platform because it's Java based, and is also rich with features.

It takes some time to warm up to **********, but once you get the feel for it, it's not that hard to use. It lets you download many large files unattended (just pick them up when they're done) and the improved network efficiency is a nice side benefit.

Best regards,
Andy
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post #12 of 654 Old 05-07-2007, 07:04 PM
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Andy,

Works fine with no referrer header. I didn't want to turn this into a design review, but... some comments on the plots. Or, as they say in work "documentation cleanup".

First, I think you may want to re-layout the output. It looks like you tried to fit everything into a portrait aspect ratio for a standard page printout. That's OK, but I think that squeezing the radar plot into the left hand corner compromised table clarity. Try orienting for landscape, or, just put the plot centered at the top of the page with the table and spectrum plot below (that's a really nice presentation).

Next, each output should echo the user input data. IOW, put the address / height / coordinates (depending on entry) at the top of the page. There's no way I can tell what the plot represents when I return to it later. Filenames aren't going to do it.

IMHO, the table needs to convert the output variables into "English". You need to make it easy on the user- they're having enough trouble to figure out the colors.

Suggest:
Callsign - OK as-is

Channel - Split into 2 columns: Broadcast on Channel, Digital Channel ID. For example, 43/52.1 is confusing. I understand you want to save space, but it's very easy to simply add a row to the header, like:
_______ Broadcast_____Digital (used underscores to indent for this post)
_______on Channel___Channel ID
__________43_________52.1

I'm a bit fuzzy on the last 2 columns for height. Long day here...
LOS_h - Is this for elevation angle = 0 looking back to transmitter? I'm not quite clear on this. The FAQ didn't help. Perhaps to change the header to "Minimum Height" (also change FAQ).
LOS_min - Is this the height to get out of the diffraction area? FAQ didn't help here either. Perhaps to change the header to "Clear path LOS height" (also change FAQ).

An aside on spectrum analyzers- many people forget that they are really voltmeters. The front end is a diode detector that measures voltage and calculates power. That can get interesting under harsh conditions.

I just had a few comments on the output content - this is excellent work.
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post #13 of 654 Old 05-08-2007, 04:51 AM
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SSSHHHHH!! Don't tell him stuff like that! He will clean it up and then start charging us for it!

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post #14 of 654 Old 05-08-2007, 05:41 AM
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Quote:


I always felt that antennaweb was dumbed-down too much. Colored wedge charts give very little real information, and I'm not sure that it's helping make the consumer's life any easier.

Glad someone else agrees with me. Those charts don't tell you squat. People don't realize it's from the CEA, what would you expect?

Four issues/ suggestions;
1. The received signal strength is way off the mark. Levels around 0dbm (stations 7 miles out) show up as -30dbm on the chart for example.
2. Levels above -20dbm run into the list directly above the graph.
3. Those same stations located east of your location (right of the pie chart) run into that list also.
4. The spreadsheet, there is alot of info there, but it is kinda hard to read. It would help if it was larger and there were spaces between each line.

Those two last columns the previous poster mentioned, the numbers for each don't seem to be consistent.

Your idea has some real potential.
LL

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post #15 of 654 Old 05-08-2007, 07:11 AM
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Personally, I was blown away by the site. It's a HUGE help, especially for someone just getting into this whole antenna thing (again after 40 years...). I need to check when I get home as to whether I can enlarge the .png and split out the radar map from the rest.

I also noticed the azimuth numbers are different from what I've found elsewhere as far as telling me where those towers are. Either your numbers need to be adjusted for declination or everyone else's are wrong OR.... maybe *I'm* wrong!

Anyways... declination by zip code should be easy (for the US)
http://www.ngdc.noaa.gov/seg/geomag/jsp/struts/declZip

I want to see if I can laminate and mount the radar print and attach it to my mast
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post #16 of 654 Old 05-08-2007, 07:40 AM
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Hey neighbor, haven't seen you in the local thread;
http://www.avsforum.com/avs-vb/showthread.php?t=137214

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Abundant OTA television is what makes this country different from all others. Lets keep it this way. If you like Wi-Fi so much, OTA fits right in. After all, it is wireless.
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post #17 of 654 Old 05-08-2007, 01:46 PM - Thread Starter
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Quote:
Originally Posted by GeekGirl View Post

First, I think you may want to re-layout the output. It looks like you tried to fit everything into a portrait aspect ratio for a standard page printout. That's OK, but I think that squeezing the radar plot into the left hand corner compromised table clarity. Try orienting for landscape, or, just put the plot centered at the top of the page with the table and spectrum plot below (that's a really nice presentation).

Next, each output should echo the user input data. IOW, put the address / height / coordinates (depending on entry) at the top of the page. There's no way I can tell what the plot represents when I return to it later. Filenames aren't going to do it.

IMHO, the table needs to convert the output variables into "English". You need to make it easy on the user- they're having enough trouble to figure out the colors.

Suggest:
Callsign - OK as-is

Channel - Split into 2 columns: Broadcast on Channel, Digital Channel ID. For example, 43/52.1 is confusing. I understand you want to save space, but it's very easy to simply add a row to the header, like:
_______ Broadcast_____Digital (used underscores to indent for this post)
_______on Channel___Channel ID
__________43_________52.1

I'm a bit fuzzy on the last 2 columns for height. Long day here...
LOS_h - Is this for elevation angle = 0 looking back to transmitter? I'm not quite clear on this. The FAQ didn't help. Perhaps to change the header to "Minimum Height" (also change FAQ).
LOS_min - Is this the height to get out of the diffraction area? FAQ didn't help here either. Perhaps to change the header to "Clear path LOS height" (also change FAQ).

Thanks! These are fantastic suggestions. This is definitely a work in progress, so it's the perfect time to make changes that improve the software. This started as a very technical engineering tool I used for personal reference, so I know I need to clean up the UI for general consumption. I like your ideas a lot.

I think I will end up removing the LOS_h and Min_h columns altogether.

I also think it's safe to shrink the radar plot, leaving more space for the table, and keeping the layout roughly the same.

FYI, there's a subtle requirement of trying to make everything fit within an 800x800 image. That's because most vBulletin based forums restrict image uploads to that size. My hope was to make it easy for people to upload their plots when posting to forums like this when asking for help. By encapsulating all the really useful information in a single image attached to a post, it makes it easier for people like me to respond to people's questions. If this constraint begins to be a problem, then I have no problem with giving up on this idea.

My philosophy is 1) make it work, 2) make it work well, and 3) make it faster/cheaper/better.

Best regards,
Andy
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post #18 of 654 Old 05-08-2007, 02:39 PM - Thread Starter
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Thanks for the pointers! Let me expand on these one at a time:

Quote:
Originally Posted by videobruce View Post

1. The received signal strength is way off the mark. Levels around 0dbm (stations 7 miles out) show up as -30dbm on the chart for example.

The levels are actually only about 10 dB too low. That's because I'm using F(99,99) parameters in the Longley-Rice modeling. Those are really worst case conservative conditions, so it definitely predicts power levels lower than the average. I will probably shift all the values up by 10 dB to bring things in line with reality (based on what I've measured in field tests).

I suspect the other 20 dB difference you're seeing is probably because of your receiver setup. Keep in mind that the L-R modeling is predicting the field strength "in the air". If you are measuring something on a meter or spectrum analyzer, you're actually including gain/loss from your antenna, amps, cables, and connectors.

I don't expect anyone to actually be able to reproduce the Rx_dBm numbers via measurement because we generally don't work with perfectly tuned dipoles or isotropic antennas. The data is supposed to show what raw signal you have to start with, and then it's up to individual selection of antennas, amps, cables, and receivers to make the most out of what's there.



Quote:


2. Levels above -20dbm run into the list directly above the graph.
3. Those same stations located east of your location (right of the pie chart) run into that list also.

I think I will need to place an upper bound on the bar lengths / positions on both the radar and spectrum plots. This will prevent the graphics from running into the text.



Quote:


4. The spreadsheet, there is alot of info there, but it is kinda hard to read. It would help if it was larger and there were spaces between each line.

I will be experimenting with expanding the table. It's probably the most informative part of the analysis and deserves the most attention. You may see several variations over the next few days while I try out different ideas.



These are all excellent observations and I'll try my best to make things better!


Thanks a bunch.


Best regards,
Andy
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post #19 of 654 Old 05-08-2007, 04:08 PM
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Andy - TWO TUMBS WAY WAY up!!!

You've done an absolutely totally and completely fantabulious job!

This was one of my complaints about the online OTA HDTV scene - there were no Google Earth placemarks for towers, and reception prediction was limited to Antennaweb

One of my other complaints was the lack of a Wiki dedicated to antennas, DMA's, etc..

I'm working on a Wiki with the following:
-An index and articles for antennas and reception hardware
-Pages for each DMA which have links to local forums, their AVS-Forum thread, information about local antenna installers, places to buy parts, etc....
-A large, in-depth section about installation, reception issues, etc, etc ,etc.....

I should hopefully be announcing it in a month or two. (It still needs a lot of work). Does this sound like a good idea, or did somebody else do it first?

Any things I should add?
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post #20 of 654 Old 05-08-2007, 05:23 PM
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Quote:
Originally Posted by andy.s.lee View Post

The levels are actually only about 10 dB too low. That's because I'm using F(99,99) parameters in the Longley-Rice modeling.

Andy,

I suspect you already know this, but in case you don't, DTV TV stations, service is defined by the FCC to exist where the received signal strength exceeds the limit shown in the following table, using the F(50,90) propagation curves.

Channels DTV Noise-Limited Service Minimum Field Strength over Community of License
Channels 2 through 6 28 dBu 35 dBu
Channels 7 through 13 36 dBu 43 dBu
Channels 14 through 69 41 dBu 48 dBu

Keep up the great work!!

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post #21 of 654 Old 05-08-2007, 06:02 PM
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There was another site I used to goto that had alot of this info on, but it seems to have disappeared. This is a Very satisfactory replacement (especially with some of the other suggestions above).

You CAN put antennas on your owned and/or controlled property...
http://www.fcc.gov/mb/facts/otard.html

Being A Beacon of Knowledge in the darkness of FUD
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post #22 of 654 Old 05-08-2007, 06:30 PM
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Quote:
Originally Posted by andy.s.lee View Post

My philosophy is... 3) make it faster/cheaper/better.

And the unmentioned part- Pick any 2.

Removal of LOS_h and Min_h : Probably a good idea, since most people will interpret the charts to mean the signal level at the user's AGL antenna height. I assume that's what LOS_h meant (got confused from the FAQ).

I think putting some form of user data on the legend is very important. At least the antenna height and a lat/lon or street / zip.

Bug report (getting serious here!): Entering an invalid street address and AGL in feet returns no error message with an AGL in meters.
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post #23 of 654 Old 05-08-2007, 08:17 PM
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Andy,

Absolutely great site. I have a couple of constructive comments.

The radar plot seems to be redundant since the bar graph depicts the same information without the overlap of several channel numbers in the same pixel space, which are unreadable. I could live with eliminating the radar plots - would free up a lot of page space. I did notice, though, that not all of the channels listed to the right of the radar plot are listed on the bar graph. Any reason for this?

Regarding the LOS_h and Min_h values, one appears to be incorrect for my address. It is KFCT, 21/22-1. The Min_h value is larger than the LOS_h value. Shouldn't it be the other way around? Or do I not understand what these values are meant to indicate?

Several of the digital stations listed for my address are under STA's, not on the air currently, and probably won't be on the air until 2-17-09 (flashcutting). I don't believe the FCC database gives on air info for STA's but is there some way to eliminate stations that aren't on the air from the listings?

Finally, and this may be a dumb question, but what does 1 Edge and 2 Edge mean? Are these somehow related to the LOS_h and Min_h values?
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post #24 of 654 Old 05-08-2007, 10:09 PM - Thread Starter
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Originally Posted by foxeng View Post

Andy,

I suspect you already know this, but in case you don't, DTV TV stations, service is defined by the FCC to exist where the received signal strength exceeds the limit shown in the following table, using the F(50,90) propagation curves.

Channels DTV Noise-Limited Service Minimum Field Strength over Community of License
Channels 2 through 6 28 dBu 35 dBu
Channels 7 through 13 36 dBu 43 dBu
Channels 14 through 69 41 dBu 48 dBu

Keep up the great work!!

Thanks!

Yep. I'm quite familiar with the FCC TV guidelines. They've already added fudge factors to account for building penetration losses, antenna gain, and receiver sensitivity to come up with these numbers. However, as many avsforum members know, every situation is different, so sometimes those assumptions can be way off.

It's easy to be critical of the FCC, but I also have to give them credit. Afterall, if they hadn't made the transmitter database available for public download, I wouldn't be able to make any of these tools. We also have to keep in mind that a lot of these guidelines are based on work originally started in the 1950s and 60s. It's only recently that computer processing power has become good enough to really analyze these signals in detail.

BTW, I use F(99,99) modeling parameters instead of F(50,90) because it's generally known that the FCC parameters are a bit too generous (by roughly 10 dB, it seems). By design, my modeling results will show more pessimistic numbers than the FCC model, but in my experience, this is a better match for real-world viewing experience.

Best regards,
Andy
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post #25 of 654 Old 05-08-2007, 10:20 PM - Thread Starter
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Originally Posted by GeekGirl View Post

I think putting some form of user data on the legend is very important. At least the antenna height and a lat/lon or street / zip.

I think I will add the option to enter a user specified title to the top of the plot. I purposely left out any user-identifiable information in the plots because most people would prefer to keep their address and/or coordinates private. I think a short text field for a title will let people label each plot however they please (e.g., "Dave's House 30ft Mast") without giving away any secrets.



Quote:
Bug report (getting serious here!): Entering an invalid street address and AGL in feet returns no error message with an AGL in meters.

I'm not entirely clear on what you mean by this, but I THINK you're saying that if there's an error in the submitted form and the form re-appears partially filled-in, then the value in the recieve height field is filled in with the meters value instead of the originally entered feet.

If I'm reading this right, then I suspect you're exactly right. I had not accounted for this case. I'll need to clean this up in a better way the makes sure the metric stuff doesn't get intermingled with the user entered data. I should have this fixed by tomorrow.

Nice catch, thanks!


Best regards,
Andy
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post #26 of 654 Old 05-08-2007, 11:41 PM - Thread Starter
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Quote:
Originally Posted by milehighmike View Post

I have a couple of constructive comments.

The radar plot seems to be redundant since the bar graph depicts the same information without the overlap of several channel numbers in the same pixel space, which are unreadable. I could live with eliminating the radar plots - would free up a lot of page space.

Comments are always welcome!

The radar plot serves a few different purposes, actually. The main purpose is for visualization of transmitter directions. This makes it easier to spot the need for omni antennas, directional antennas, rotators, or some combination of the above.

If the antenna radiation pattern (polar plot) is known, we can imagine that pattern overlaid on the radar plot to roughly know whether the beam width is too wide/narrow to capture signals from multiple tower clusters.

For anyone installing an antenna, it also doesn't hurt to have the radar plot on hand to make sure everything is aimed correctly. I know that sometimes I've mis-calculated my azumuths and ended up installing antenna "trees" that didn't match my plot. Once I see that I've made a mistake, I can go through my caclulations again and see what I did wrong.



I agree that the radar plot isn't super important relative to the screen real-estate that it takes up, so I do plan on shrinking its size. That should create a lot more space to make the table bigger.



Quote:


I did notice, though, that not all of the channels listed to the right of the radar plot are listed on the bar graph. Any reason for this?

Both the radar plot and the spectrum graph have limits on their scale. The bulls eye of the radar plot is currently at -110 dBm, so it won't show any signals below that. The bottom edge of the spectrum graph is -120 dBm, so it will also cut off some transmitters. These cutoff values are generally very low, so the majority of people will not be able to receive signals below these levels anyway. The table tries to list as much information as possible within the space allowed, down to about -130 dBm. This goes well beyond the reach of most people, so the weakest transmitters shown will not have much value except maybe for DXers.



Quote:


Regarding the LOS_h and Min_h values, one appears to be incorrect for my address. It is KFCT, 21/22-1. The Min_h value is larger than the LOS_h value. Shouldn't it be the other way around? Or do I not understand what these values are meant to indicate?

I will be removing these columns soon since they don't help much and they created a lot of confusion. However, since you asked...

The LOS_h is the height where you'd start getting a line-of-sight path to the transmitter. That's the height where the path is just at the grazing edge of clearing the obstruction.

The Min_h is the height necessary to get a signal level of at least -100 dBm. Because of the way diffraction works, the signal strength at the grazing edge path is actually lower than the signal at slightly higher or lower elevations. It is actually possible to get a stronger signal below the grazing edge path than at the grazing edge path. The search algorithm to find this minimum height probably homed in on the local-maxima just above the grazing edge path to reach the -100 dBm cutoff. If this transmitter was any further away, it probably would have found no height sufficient to reach -100 dBm.

It's just one of those interesting "spooky" thinks about EM waves, but this information is hardly any use to people using the tools. The original idea for this column was to help people decide how high they should build a mast to get a channel that's just slighly out of reach. It will be removed soon.

I might want to put in a column for distance to nearest terrain obstacle or angle/severity of diffraction, but I'll have to think about this some more.



Quote:


Several of the digital stations listed for my address are under STA's, not on the air currently, and probably won't be on the air until 2-17-09 (flashcutting). I don't believe the FCC database gives on air info for STA's but is there some way to eliminate stations that aren't on the air from the listings?

Yes. If you let me know what the real transmitter is broadcasting, I will add that info to my collection of FCC database "overrides". The FCC database has all kinds of errors, missing data, and superfluous data. My software does its best to filter the database to find the records that best match reality, but there's still the need to manually put in patches for some of the transmitters. The good news is that once I enter the "override" in my database, it fixes all future generated output (including coverage maps, radar plots, and the transmitter icons collection). The overrides stay in effect even after I download new copies of the FCC database.

I don't have an automated way to do this yet. I think the only way to protect the database from abuse would be to have a community voting mechanism or a network of moderators, but that's not something I'm prepared to set up right now.



Quote:


Finally, and this may be a dumb question, but what does 1 Edge and 2 Edge mean? Are these somehow related to the LOS_h and Min_h values?

Those indicators show the dominant path of the signal between the transmitter and your location. 1- and 2- Edge stand for single- or double- edge diffraction, which means that the transmission path is most like the bending of waves over one or two edges (terrain high-points, in this case). Diffraction is very common and a lot of people get strong TV signals even if they're slighly blocked by 1 or 2 ridges. Line-of-sight is not necessary for good TV reception, but diffraction can weaken signals significantly, depending on how sharp the angle of diffraction is.

Increasing antenna height for a diffracted signal can improve things significantly (depends on distance to obstruction and wavelength of signal), whereas a LOS signal will hardly improve at all with added height.



These are all great topics, and I hope my answers helped! Please keep all the good ideas and feedback coming.



Best regards,
Andy
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post #27 of 654 Old 05-09-2007, 06:39 AM
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The LOS_h is the height where you'd start getting a line-of-sight path to the transmitter. That's the height where the path is just at the grazing edge of clearing the obstruction.

The Min_h is the height necessary to get a signal level of at least -100 dBm. Because of the way diffraction works, the signal strength at the grazing edge path is actually lower than the signal at slightly higher or lower elevations. It is actually possible to get a stronger signal below the grazing edge path than at the grazing edge path. The search algorithm to find this minimum height probably homed in on the local-maxima just above the grazing edge path to reach the -100 dBm cutoff. If this transmitter was any further away, it probably would have found no height sufficient to reach -100 dBm.

this info is helpful to me...can you use a yes or no option to include or not include. default to no.
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post #28 of 654 Old 05-09-2007, 07:57 AM
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Quote:


FYI, there's a subtle requirement of trying to make everything fit within an 800x800 image. That's because most vBulletin based forums restrict image uploads to that size.

But many will resize the image. If not, the poster could resize it. I think many would prefer a larger image.
Easy to reduce, hard to expand (without loosing detail).
Quote:


I suspect the other 20 dB difference you're seeing is probably because of your receiver setup. Keep in mind that the L-R modeling is predicting the field strength "in the air". If you are measuring something on a meter or spectrum analyzer, you're actually including gain/loss from your antenna, amps, cables, and connectors.

I never thought about the 'gain' factor of the antenna.
Completely missed the boat on that one.

Regarding the LOS column, I actually like this since it is a unique feature unavailable elsewhere.

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Abundant OTA television is what makes this country different from all others. Lets keep it this way. If you like Wi-Fi so much, OTA fits right in. After all, it is wireless.
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post #29 of 654 Old 05-09-2007, 12:28 PM
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Originally Posted by andy.s.lee View Post

Comments are always welcome!

It's just one of those interesting "spooky" thinks about EM waves, but this information is hardly any use to people using the tools. The original idea for this column was to help people decide how high they should build a mast to get a channel that's just slighly out of reach. It will be removed soon.

These are all great topics, and I hope my answers helped! Please keep all the good ideas and feedback coming.

Best regards,
Andy

I would miss the antenna height options. Can you make it possible to display them if the user selected that option when the location was entered? Perhaps the manual entering of antenna height will give essentially the same data, but with more steps.
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post #30 of 654 Old 05-09-2007, 12:39 PM - Thread Starter
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Originally Posted by Tower Guy View Post

I would miss the antenna height options. Can you make it possible to display them if the user selected that option when the location was entered? Perhaps the manual entering of antenna height will give essentially the same data, but with more steps.

Well, it looks like those last two columns are popular after all!

I will hold off making any changes to those columns for now. I will first experiment with shrinking the radar plot and increasing the table size. I'll try to clean up the table formatting, but will keep the columns.

Thanks everyone for the comments!



Best regards,
Andy
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