"Fine Tuning Dial" on indoor VHF/UHF Antenna

Discussion in 'Wireless & RF Design' started by cosmicsunset, Oct 24, 2013.

  1. cosmicsunset

    Thread Starter New Member

    Oct 24, 2013
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    I've noticed some indoor TV antennas have a dial on them that supposedly fine tunes the reception. Can someone explain how that works and if it's worth the added cost?

    My best guess is it's just a potentiometer to enable more exact impedance matching but I don't know if it would be matching the impedance of the output cable and TV or the antenna itself.
     
  2. Art

    Distinguished Member

    Sep 10, 2007
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    Could it be a bandpass filter, or a notch filter?
     
  3. cosmicsunset

    Thread Starter New Member

    Oct 24, 2013
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    I found this thread: http://forum.allaboutcircuits.com/showthread.php?t=65066

    and it seems that the dial is most likely a variable inductor used to match the antenna to the frequency being received.

    So if I understand correctly that means it would need to be changed when the channel was changed in order to maintain optimal reception, although I suspect most people would just find one position that worked best overall and leave the dial there.

    So I'm thinking that, all else being equal, the antennas that have tuning dials are a better option because if there's a channel the user really wants to see they might be able to pick it up by adjusting the dial. Otherwise they could just leave the dial at mid-range and it would be like having the non-adjustable model.

    Am I on the right track here?
     
    Last edited: Oct 24, 2013
  4. Metalmann

    Active Member

    Dec 8, 2012
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    In the old days, I bought several of those. Still do not understand how the dial works...
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Basically, the antenna is too small to be a good antenna at the desired frequency. It has poor gain at that frequency.

    So they attach a tuned circuit (inductor/cap etc) that will resonate at the desired frequency you want to receive, which bumps up the gain at that tuned frequency.

    The benefit is that the poor antenna will work much better at that frequency and not as good at other frequencies, the down side is that you have to "tune the antenna" when you change stations.

    Here's one example with some good info;
    http://www.iw5edi.com/ham-radio/?how-to-build-a-tuned-loop-antenna,118
     
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  6. cosmicsunset

    Thread Starter New Member

    Oct 24, 2013
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    ok, that makes sense but can't I achieve the same "tuning" simply by shortening or extending the 43" adjustable dipoles? Obviously that won't work on the UHF loop but wouldn't it be just as good as far as VHF and FM goes?

    The antenna with tuning circuit costs twice as much but IMO those prices are backwards. I just had a $300+ control module in my truck fail because *one* electrolytic capacitor leaked electrolyte all over the board and corroded a bunch of connections. So, I'd probably be willing to pay extra for an antenna that didn't have any capacitors in it at this point. lol

    The tuned loop antenna you linked to is pretty awesome but for applications with a wide range of frequencies (like TV) aren't yagi's the preferred design?

    Thanks for the good response!
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I'm really not an antenna expert, but there are some HAMs here on the forum who may see your thread.

    As far as basic "off the shelf" TV antennas go, some work well and some not so well. Testing one in your home location is the best idea, but not always practical.

    The next best thing is to talk to a T.V. guy who knows your exact reception area, and maybe does antenna installations or sales for that area. They should know exactly what works best, and can probably demonstrate it in front of you.
     
  8. cosmicsunset

    Thread Starter New Member

    Oct 24, 2013
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    Good point. You reminded me of a website that was recommended in some antenna set up instructions I read.

    www.antennaweb.org

    I put in my address and according to that I should be able to pick up 10 channels with a "yellow" antenna, which they define as:

    "You need a Small Multidirectional Antenna. The smallest of TV antennas, these receive equally well from all directions. Designs include novel-shaped disks, patch antennas and antennas that attach to satellite systems. These antennas are most effective when signal strength is highest and away from reflecting structures or low areas."

    Going up to the highest rated "purple" antenna, which has an amplifier and needs to be roof mounted and aimed would only get me an additional 8 channels.

    Since the "yellow" antenna is about as much money as I wanted to spend anyway (just bought the $10 RCA model at Walmart) I'm pretty happy to learn that it should perform well.

    Now I'm just waiting for my digital tuner to arrive from Hong Kong and I'll finally have upgraded to the new millennium!
     
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