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Quad Bay TV Antenna

Discussion in 'Scanning & Shortwave Listening' started by Retro, Feb 5, 2016.

  1. Retro

    Retro
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    Interesting lesson learned from experimentation today.

    I have a quad bay UHF television antenna. I use it along with two in-line signal boosters to power my police scanner, two television sets and an AM/FM stereo. We get 3 channels for free from a PBS tower about 30 miles away as the crow flies.



    To me, since the center conductor of an antenna is connected to the radiating portion in a CB antenna, it made sense to me that the antenna should be folded so that the smaller elements, which had continuity with the center conductor, were on the inside of the V with the larger ground plane panels behind them so that signals would be reflected off the ground panels and focused to the inside of the V where the receiving elements are. However, the opposite is true. When I folded it that way, I lost all reception, but when I reversed it so that the ground plane elements were in front facing the broadcast tower and on the inside of the V, it came in. I also found that closing up the V does not necessarily focus a weak signal in and make it stronger. A 45 degree angle seems to work the best and gives me a stronger received signal than a sharper angle.

    I also found that this UHF antenna will not pick up one other station that is in the same direction (on the same hilltop actually) that is in the Hi-VHF band. I've got a cheap-o VHF scanner antenna that picks it up "kind of", but it's in and out and takes constant adjustment. The other UHF channel works flawlessly with a signal strength that bounces between "good" and "excellent" using only the UHF antenna. I tried co-phasing the VHF and UHF antennas together since they're both passive/receive only, and the UHF channel(s) were still excellent, but the VHF channel(s) were still very weak and in/out.

    If possible, I'd like to find either a good VHF antenna to co-phase, or a good broadbanded antenna that will pick up both these UHF channels and the HiVHF channels.

    This is the antenna I've got up right now: www (dot) amazon (dot) com/gp/product/B00DHHMOUW

    Anybody have any suggestions for something I could upgrade to that might pick up the 3 UHF channels and the two VHF ones at the same time?
     

  2. RatsoW8

    RatsoW8
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    I picked up the one in the link below at Lowes. Paired it up with a pre-amp and I'm very pleased with it's performance. I have it mounted on the old Dish Network satellite mount but come spring time I'm going to get it up in the air another 15 ft. or so. Last count after I installed the pre-amp I'm picking up 25 local tv channels.

    http://www.lowes.com/pd_401200-16158-C2-V-CJM_1z0v120__?productId=50442584&pl=1
     
  3. space cowboy

    space cowboy
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    Quack Quack

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  4. DXman

    DXman
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  5. Retro

    Retro
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    Haven't gotten around to purchasing a different antenna because I've been working and doing other things and this one works pretty good for pulling in the kids' cartoons and the local police/fire radio traffic.

    Today however I did manage to get the TV antenna off the porch and mounted onto its own separate pole so I can do work on the porch. It's a 12 foot 4x4 with a 10 foot piece of galvanized steel conduit on the top that holds the antenna and a hinge plate at the bottom. I did notice something kind of weird though. When I had it all assembled and erected the pole, the signal came in when the pole was halfway up, but then went back out once it was completely vertical. When I would start to lay the pole back down, literally 6 inches of movement caused the signal to start coming in, but when it was perfectly vertical it went out. I lowered the antenna on the conduit by about 2 feet and then stood it back up and the signal came in absolutely perfect, past the green and into the blue on all 3 of our television sets. I had a theory and thought I would run it by you guys. Could this be the metal roof of our house causing reflection which is helping or hindering the signal, and 2 feet below the top just happens to be the sweet spot, or does this have more to do with the way radio waves propagate in general?

    Basic drawing attached to give a rough idea of the antenna's positioning.
     

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  6. 222DBFL

    222DBFL
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    There are so many variables and such when dealing with UHF/VHF. I found this article to be pretty interesting. This is just a small portion of the article but lays out of good info as to why things behave the way they do.
    Read this, I know it's long but well worth the time to read!! It may help explain why you are seeing what you are when moving your antenna. Have a good one man.

    The point to point transmission and reception of TV and radio signals is affected by many variables. Atmospheric moisture, solar wind, physical obstructions (such as mountains and buildings), and time of day all affect the signal transmission and the degradation of signal reception. All radio waves are partly absorbed by atmospheric moisture. Atmospheric absorption reduces, or attenuates, the strength of radio signals over long distances. The effects of attenuation degradation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, such as VHF TV signals.

    The ionosphere, a layer of the Earth's atmosphere, contains charged particles that reflect some radio waves. Amateur radio enthusiasts make use of this characteristic to help propagate lower frequency HF signals around the world: the waves are trapped, bouncing around in the upper layers of the ionosphere until they are refracted down at another point on the Earth. This is called skywave transmission. UHF TV signals are not carried along the ionosphere but can be reflected off of the charged particles down at another point on Earth in order to reach farther than the typical line-of-sighttransmission distances; this is the skip distance. UHF transmission and reception are enhanced or degraded by tropospheric ducting as the atmosphere warms and cools throughout the day. Since the wavelengths of UHF signals are comparable to the size of buildings, trees, vehicles and other common objects, reflection and diffraction affects the propagation of UHF signals, especially in built-up urban areas.

    The main advantage of UHF transmission is the short wavelength associated with its high frequency. The optimum size of an antenna is related to the length of the radio wave. The UHF antenna is stubby and short, making it smaller and less conspicuous than antennas used for lower frequency bands.

    The major disadvantage of UHF is its limited broadcast range, often called line-of-sight between the TV station's transmission antenna and customer's reception antenna, as opposed to VHF's longer broadcast range.

    UHF is widely used in cordless telephones and other two-way radio systems and whose range is short. Their transmissions do not travel far enough to interfere with other communications. Public safety, business communications and personal radio services such as GMRS, PMR446, and UHF CB are often found on UHF frequencies as well as IEEE 802.11wireless LANs ("Wi-Fi"). The widely adapted GSM and UMTS cellular networks use UHF cellular frequencies. A repeater propagates UHF signals when a distance greater than the line of sight is required.
     
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