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Thread: Receiving TV antenna HAAT curiosity

  1. #1
    Join Date
    Jul 2005
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    Springfield, Missouri
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    Default Receiving TV antenna HAAT curiosity

    I have been curious why my TV dx antennas seem to always favor reception from the south and southwest. I ran the FCC's HAAT calculator on my antenna elevation (local HAAT plus antenna height), plugged in with LAT/LONG coordinates.

    https://www.fcc.gov/media/radio/haat-calculator

    So I attached a jpeg of the results. It seems puzzling to me. It would appear that my *best* direction should be from 280 degrees to 40 degrees...from the NW - N - NE. But it seems to be my most difficult directions for receiving dx. I thought I had a ridge just to my N/NE about a 1/4 mile away, but according to the HAAT calculator, that doesn't show up. Could it be something related to weather and how it affects tropo conditions, or perhaps there is something geographic that I am not seeing. To date, my experience has been that DTV stations from NW Arkansas and Tulsa OK/sometimes OKC come in much sooner than the DTV stations in Kansas City or even central MO for that matter.

    I appreciate your comments or opinions.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	FCC HAAT chart 37-15-45N 93-22-50W.jpg 
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ID:	19947  
    Jim Thomas
    Springfield, MO

    Ozark Mountain DTV dxing Daredevil

    Dx Equipment - AntennaCraft MXU59 UHF antenna & homebrew version of AntennaCraft Y10-7-13 VHF antenna @ 25'. Both antennas fed through a Winegard HDP-269 12dB pre-amp; a Zenith DTT901 converter box & a Silicon Dust HDHomerun Dual ATSC tuner, using Rabbitears autologger support.

  2. #2
    Join Date
    Sep 2008
    Location
    Alexandria, VA, US
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    Default

    Jim,

    Sorry I hadn't answered your e-mail on this issue yet, but just as well to answer it here where all can see.

    HAAT along a radial is calculated by taking a sample every 0.1 km over a collection of points varying from 3.2 to 16.1 km from the center point. As such, your 1/4 mile ridge gets ignored in the calculation. When a transmitter is at the top of a tower several hundred or more than a thousand feet up, the terrain within 3.2 km can be ignored, and so it is.

    I would also point out that particular tool is using the GLOBE 30-second terrain database, which pretty low resolution. Better terrain data would likely get you a better answer.

    - Trip
    Come visit RabbitEars for all your digital TV subchannel informational needs.

    Comments are my own and not that of the FCC (my employer) or anyone else.

  3. #3
    Join Date
    Dec 2010
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    Poughkeepsie, NY
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    Default

    Jim, is the top of the ridge just a 1/4 mile away? At that proximity, it wouldn't take much ridge height to give you serious reception problems. I would think a ridge elevation of even 50 feet higher than your antenna height would give serious issues, at least on UHF. On the bright side, any terrain shielding from the North or Northeast should provide a reduction of CCI, allowing better reception to the S or SW.
    Chris - Poughkeepsie, NY
    DTV DXer since April 2009
    DTV DX screenshots at: http://www.flickr.com/photos/dtvdxer/sets
    DTV DX Videos at: http://www.youtube.com/user/dtvdxer

  4. #4
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    The ridge is roughly 1/4 mile to the north and northeast, with an increase in elevation of almost 200'. I have consulted topographic maps and also the internet interactive type, where you move a cursor on the map and it tells you the elevation as you move the cross hair cursor around. They all confirm there is a rise in the elevation to my north and northeast.
    Jim Thomas
    Springfield, MO

    Ozark Mountain DTV dxing Daredevil

    Dx Equipment - AntennaCraft MXU59 UHF antenna & homebrew version of AntennaCraft Y10-7-13 VHF antenna @ 25'. Both antennas fed through a Winegard HDP-269 12dB pre-amp; a Zenith DTT901 converter box & a Silicon Dust HDHomerun Dual ATSC tuner, using Rabbitears autologger support.

  5. #5
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    Pleasant View, TN EM66
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    You might try the Communications Research Centre's Predict online Longley-Rice calculator.

    Work it "backwards" -- put in the antenna height of your *receiver* antenna where it asks for a *transmitter* antenna, and put the height of the *transmit* antenna where it asks for a *receiver*. (I just put in 300 meters since as DXers we're dealing with multiple transmitters)

    You have to put in a "power" for your receive site -- I found 100 watts makes for a decently readable map.

    Don't forget to set the Rx Area. It doesn't automatically set it to match the specified "transmitter" coordinates; if you don't tell it to estimate coverage in southwest Missouri it will calculate it for the vicinity of Ottawa, Ontario. (and show no coverage whatsoever )

    I just ran it for my system. It shows a notch to the southeast (which I didn't know I had) and one to the east-northeast. (of which I'm too well aware)

    We also ran it "forwards" before filing for W279CH, just to show the applicant what to expect. The actual results once the translator was built match the Predict output pretty well.
    Doug Smith W9WI
    Pleasant View, TN EM66
    http://www.w9wi.com

  6. #6
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    As Doug suggested, I ran the Longley-Rice calculator. The predicted pattern plot is attached. It pretty much shows what the FCC calculator shows. I can't *see* that it shows anything that favors a certain direction. I also see the notches that Doug refers to, but not sure what to make of that.

    Just for kicks I plugged in 20dB for antenna gain, since I am using a pre-amp on my antennas, with the antenna bearing at 0.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Longley-Rice antenna pattern.jpg 
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ID:	19948  
    Last edited by Jim Thomas; 01-11-2017 at 08:12 PM.
    Jim Thomas
    Springfield, MO

    Ozark Mountain DTV dxing Daredevil

    Dx Equipment - AntennaCraft MXU59 UHF antenna & homebrew version of AntennaCraft Y10-7-13 VHF antenna @ 25'. Both antennas fed through a Winegard HDP-269 12dB pre-amp; a Zenith DTT901 converter box & a Silicon Dust HDHomerun Dual ATSC tuner, using Rabbitears autologger support.

  7. #7
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    What did you put in for an antenna height at the "transmitter" end? The default is pretty high (50m IIRC) and could get it over the top of your ridge.

    The notches are places where terrain rises and reduces signals; the "bumps" (towards the middle of the Ozark National Forest, for example) are places where terrain falls. They're considerably more dramatic on my map which I think reflects my rather low antenna. (I used 2 meters for my antenna height)

    Antenna gain figures just "fudge" the power -- putting in 100 watts and an antenna gain of 20dB has essentially the same results as putting in 10,000 watts and an antenna gain of 0dB. But your plot isn't clipping -- you defined the reception area as large enough to encompass everywhere the pattern goes -- so that's not a problem.
    Doug Smith W9WI
    Pleasant View, TN EM66
    http://www.w9wi.com

  8. #8
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    Per Doug's question about antenna height, I *think* I put in 391 meters. I'm not sure now, but that's probably not right. I was thinking I needed to put the HASL for my LAT/LONG plus the antenna height, the same as I did for the FCC calculator.

    And then, aha! I knew there was a ridge lurking to my north in my local topography! I got these images from....

    http://www.heywhatsthat.com/

    I remembered today that Pat Dyer told me about that website a few years ago and I had to do a little snooping on the internet to find it, as I couldn't remember the name. In the bottom terrain view on each image, on the left you will see the purple dot, which represents the location for my antennas. It looks across the terrain and shows you how the terrain changes. The ridge I was estimating was 1/4 mile is actually about 1/10 mile from my location.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Springfield MO topography - east view.jpg 
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Name:	Springfield MO topography - north view.jpg 
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Name:	Springfield MO topography - south view.jpg 
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Name:	Springfield MO topography - west view.jpg 
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    Last edited by Jim Thomas; 01-12-2017 at 03:21 PM. Reason: Corrections
    Jim Thomas
    Springfield, MO

    Ozark Mountain DTV dxing Daredevil

    Dx Equipment - AntennaCraft MXU59 UHF antenna & homebrew version of AntennaCraft Y10-7-13 VHF antenna @ 25'. Both antennas fed through a Winegard HDP-269 12dB pre-amp; a Zenith DTT901 converter box & a Silicon Dust HDHomerun Dual ATSC tuner, using Rabbitears autologger support.

  9. #9
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    Poughkeepsie, NY
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    735

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    Jim...

    Out of curiosity, I ran a terrain profile to the NNE based on your co-ordinates shown in this thread. I used KNLJ (Jefferson City) as the northern end-point. Your location is at the left of this chart, and KNLJ is on the right side. I was very surprised not only to NOT see any ridge in your proximity, but also just how nice a spot you are in (terrain-wise) for DX to the NNE. By the way, KNLJ's antenna is over 1750 feet above sea level, and way beyond the top of this graph.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Jim Thomas - KNLJ.jpg 
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ID:	19953  
    Chris - Poughkeepsie, NY
    DTV DXer since April 2009
    DTV DX screenshots at: http://www.flickr.com/photos/dtvdxer/sets
    DTV DX Videos at: http://www.youtube.com/user/dtvdxer

  10. #10
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    Chris, what program do you use to generate that plot?
    Jim Thomas
    Springfield, MO

    Ozark Mountain DTV dxing Daredevil

    Dx Equipment - AntennaCraft MXU59 UHF antenna & homebrew version of AntennaCraft Y10-7-13 VHF antenna @ 25'. Both antennas fed through a Winegard HDP-269 12dB pre-amp; a Zenith DTT901 converter box & a Silicon Dust HDHomerun Dual ATSC tuner, using Rabbitears autologger support.

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