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post #31 of 40 Old 11-24-2018, 08:18 PM
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Quote:
Originally Posted by ProjectSHO89 View Post
Cell size was my initial and primary concern.

However, is there a reason they moved to using dbuv/m for the calculated Rx signal strength value instead of dBm as the previous version used? I need a primer on how to correlate the two numbers.
As I said, once I hear back, I'll pass it along.

The reason is that TVStudy calculates dBuV/m rather than dBm. The new RabbitEars TVStudy mode uses it too, and for the same reason.

I don't have the entire formula handy, but I can get it when I'm back at work. (It's not something I work with terribly often.) The short version, however, is that 28 (low-V), 36 (high-V), and 41-(20*log(615/freq)) (UHF) dBuV/m roughly line up with the -84 dBm number you're familiar with.

- Trip
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post #32 of 40 Old 11-25-2018, 12:49 PM
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Quote:
Originally Posted by ProjectSHO89 View Post
Cell size was my initial and primary concern.
0.5 km.

- Trip

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post #33 of 40 Old 11-25-2018, 02:07 PM
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TVFool came back on-line last night....keep your eyes open to changes...esp. more accurate Station dBase????
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post #34 of 40 Old 11-26-2018, 09:56 AM
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Quote:
Originally Posted by Trip in VA View Post
As I said, once I hear back, I'll pass it along.

The reason is that TVStudy calculates dBuV/m rather than dBm. The new RabbitEars TVStudy mode uses it too, and for the same reason.

I don't have the entire formula handy, but I can get it when I'm back at work. (It's not something I work with terribly often.) The short version, however, is that 28 (low-V), 36 (high-V), and 41-(20*log(615/freq)) (UHF) dBuV/m roughly line up with the -84 dBm number you're familiar with.

- Trip

I have not seen a good explanation of what dBuv/m is. If I understand it, dBuv/m refers to an RF field and not an actual signal strength. It's dBuv over a length of 1 meter. So the signal strength in uV is what you'd get if you used an antenna of 1 meter in length at any frequency ignoring mismatch issues. You can't just say a dBuv/m value of X equals a dBm value of Y because that's dependent on the frequency of the antenna (its size) and its gain. A dipole at low VHF produces a much stronger signal than a dipole at UHF in the same dBuv/m field because the antenna is larger. I do understand why it's used in calculations because it is independent of frequency and antenna gain. I don't find dBuv/m to be particularly useful until it's converted to the frequency of interest and antenna you have.

In summary, dBuv/m is an RF field strength. An antenna placed in this field generates a signal strength in dBm at the antenna terminals.

Somebody please set me straight if I have this wrong.
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post #35 of 40 Old 11-26-2018, 11:28 AM
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Quote:
Originally Posted by Calaveras View Post
In summary, dBuv/m is an RF field strength. An antenna placed in this field generates a signal strength in dBm at the antenna terminals.

Somebody please set me straight if I have this wrong.
My understanding is the same as yours. I also don't find it as useful as dBm. My previous post gives a more complete description of my understanding.

Why dBµV/m instead of dBm for a report
http://01966633.com/forum/25-hd...l#post57158748

The Signal Margin in a TVStudy report is similar to the Noise Margin in a TVFool report, so we at least have that and the Good, Fair, Poor, Bad ranking easily understood by anyone.




This is a TVFool report for the same location for comparison:
http://www.tvfool.com/?option=com_wr...90380ded068056



There is no obvious way to enter coordinates for a TVStudy report, so use this as a template and enter substitute coordinates:

http://www.rabbitears.info/search.php?request=zip_search&zipcode=&miles=80&ad dress=&lat=48.452621&lon=-123.342328&sorting=signal&tvstudy=Y&dbtype=dBm&height=20

Before the TVStudy software was added to rabbitears.info, I used the dBm reports but found they were not as accurate for my location, and they took much longer to come up.

I find it useful to see the rabbitears.info dBuV/m report AND the TVFool report for a location, especially since there are often errors in the TVFool database used to generate reports.

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 11-26-2018 at 07:54 PM.
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post #36 of 40 Old 11-27-2018, 12:34 PM
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Using the FCC DTV maps site in Canada

Out of curiosity, I tried using the FCC DTV maps site for the above gavorney Canadian location in Victoria BC.

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post #37 of 40 Old 11-28-2018, 02:05 PM
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How the FCC Calculates the Minimum Required Field Strength in dBuV/m for Reception

Quote:
Originally Posted by Calaveras View Post
I have not seen a good explanation of what dBuv/m is.
There is a pretty good explanation of the origin of dBuV/m in this FCC document:

Digital Television Field Strength Standards
And Testing Procedures
FCC 05-199, Adopted: December 6, 2005
http://transition.fcc.gov/oet/info/documents/reports/SHVERA/SHVERA-FCC-05-199.pdf

pp 9-10
13. The noise-limited digital TV field strength standards were derived from a set of assumptions for the several technical planning factors that are present in a typical DTV receiving system and for a defined level of service......These factors and their assumed values as used in establishing the DTV noise-limited service area field strength intensity standards are:



14. Using the factors in the above chart, the minimum signal level that needs to be present at the input terminal of a television receiver, to provide service is the sum of the thermal noise, the receiver noise figure, and the receiver signal-to-noise (S/N) ratio, that is:

Minimum receiver signal level R = Nt + Ns+ S/N
for low and high VHF channels = -106.2 + 10 + 15.2 = -81.0 dBm
for UHF channels = -106.2 + 7 + 15.2 = -84.0 dBm

15. Considering the entire receiving system, the minimum field strength needed to be available at the antenna is the sum of the minimum signal level needed at the receiver, the downlead line loss, and the dipole factor, less the antenna gain:

Minimum field strength to receive service MFS = R + L + Kd – G
for low VHF channels = -81.0 dBm + 1 + 111.8 – 4 = 27.8 dBμV/m
for high VHF channels = -81.0 dBm + 2 + 120.8 – 6 = 35.8 dBμV/m
for UHF channels = -84.0 dBm + 4 + 130.8 – 10 = 40.8 dBμV/m

16. Rounding to the nearest decibel, we have 28, 36, and 41 dBu as the minimum field strength
standards for channels in the low VHF, high VHF, and UHF channel bands, respectively.
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Last edited by rabbit73; 11-28-2018 at 06:04 PM.
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post #38 of 40 Old 11-28-2018, 03:02 PM
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Quote:
Originally Posted by rabbit73 View Post
[FONT=Arial]There is a pretty good explanation of the origin of dBuV/m in this FCC document:

Wow. There's a lot in that document! These paragraphs ought to be required reading for anyone wanting to use an indoor antenna:

22. Inherent in the Commission’s definition of digital television service area are certain assumptions regarding the receiving antenna. For DTV, the Commission assumes that the receiving antenna is located outdoors at a height of 9 meters above ground.43 In addition, the Commission’s procedures for evaluating DTV service areas set forth specific values for antenna gain that depend upon the specific DTV channel band, namely, 4 dB for low VHF, 6 dB for high VHF, and 10 dB for UHF and assume that the antenna is oriented in the direction which maximizes the values of the field strength received for the signal being measured.44

39. Contrary to EchoStar, the NAB and the Network Affiliates argue that indoor antennas should not be considered in the DTV signal strength standards.107 They submit that it would be unfair to broadcasters to assume that viewers will use only indoor (or low-quality outdoor) antennas in determining whether DBS subscribers are eligible to receive retransmitted digital network signals. The NAB states that it is specifically because indoor antennas perform so poorly that they should not be considered for defining DTV service.108 It further states that introducing an assumption that consumers would use indoor antennas would be contrary to one of the most fundamental assumptions of the Commission's entire DTV planning process, leaving broadcasters in the position of having built a system to Commission specifications that the Commission would not deem as adequate because it is not designed to provide service to indoor antennas.109 The NAB and MSW also state that, had the Commission assumed use of indoor antennas in the planning the digital TV transition, that process would have been radically different, with stations needing enormously higher power levels to reach indoor antennas 50 to 60 miles away.
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post #39 of 40 Old 11-29-2018, 04:49 AM
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Quote:
Originally Posted by rabbit73 View Post
There is a pretty good explanation of the origin of dBuV/m in this FCC document:
Digital Television Field Strength Standards
And Testing Procedures
FCC 05-199, Adopted: December 6, 2005
http://transition.fcc.gov/oet/info/documents/reports/SHVERA/SHVERA-FCC-05-199.pdf
That is exactly what I was going to dig up at the office, should I have gotten there any time soon. (Teleworking all week.) I couldn't remember which document it was but knew it was sitting in my office. Excellent find!

- Trip

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post #40 of 40 Old 11-29-2018, 08:25 AM
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Quote:
Originally Posted by Trip in VA View Post
That is exactly what I was going to dig up at the office........ Excellent find!

- Trip
Thank you. I got lucky at Google. It came up third on the list with the search term

fcc minimum dBu pdf


Update 12-1-2018:
I tried that search term again, and it didn't work; the Google search algorithm had changed, so I really was lucky. I had to enter FCC 05-199 or Study of Digital Television Field Strength Standards, neither of which I would have known.


This also did work today
fcc minimum field strength pdf
or
fcc minimum field strength standards pdf

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 12-01-2018 at 07:29 PM.
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