Television Aerial Signal Amplifier

Discussion in 'General Electronics Chat' started by JUAN DELA CRUZ, May 29, 2008.

  1. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Hi everyone 8)
    I'm seeking for a "VHF & UHF signal amplifier for television".

    I browse the internet & found different signal amp. ckt. but there gain is to low(i.e. 10dB-20dB.)

    I need to boost the aerial signal much higher.

    Here in my country, majority of homes rely on the traditional aerial antenna w/c give there T.V. a weak signal. For the reason that cable system are available only here in the city.

    Hence, I want to build a TV aerial signal amp to increase the weak aerial signal going to there TV sets & sell to them for low cost.
    WAITING FOR YOUR FAVORABLE RESPONSE :)

    Thank you
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    The antenna is as important as the amp. The antenna you're using has a gain number attached somewhere. Generally, the more directional the antenna the higher the gain, both are good things. Do you have a rotor on your antenna, also a must for DXing weak signals.
     
  3. Gadget

    Distinguished Member

    Jan 10, 2006
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    The way I read it, is you want a Distribution amplifier. If you want to supply a neighbourhood over a wide range of frequencies, you not only want gain, but some decent sized output devices, as what you will have is a Wideband RF transmitter of several watts output.

    If it is just to boost the signal from an antenna, unfortunately amplifiers arn't a magic cure, as an amp cannot replace what has been lost, they can only really compensate for loss's in the system (after the amp). As the previous user said, start with the antenna.
     
    Last edited: May 29, 2008
  4. SgtWookie

    Expert

    Jul 17, 2007
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    A better antenna is a much better approach than a higher-gain broadband amplifier.

    Amplifiers all have a signal-to-noise ratio; in general, the higher the gain, the higher the induced noise.

    Antennas do not add noise, as they are passive elements. The better the design of the antenna, the higher the signal gain. There is no S/N penalty as with active devices.
     
  5. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Thank you very much for your reply:)

    I'm really sorry about my English language;)

    What I want is a ckt that can amplify aerial signal (VHF signal) before going to a TV.

    I've search in google and I found this ckt.
    Its gain is only 20dB

    .....HOW CAN I INCREASE ITS OUTPUT TO approx.......50dB????
    Help me to modify this ckt.:)

    Thank you once again
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    I hate to say this, but even if you get the gain up there it will likely not work. That signal to noise Sarge mentioned is a killer. The other thing is with that kind of gain the odds that you will max out the signal is quite high, there is a reason most receivers (including TVs) have an automatic gain control. The signal can only get so big before the amp starts distorting it. Distortion ruins the signal.

    I have practiced the art of DX (distant receiving) with TV antennas, with excellent results. It can be broken down into about 3 areas.

    1. Altitude is your friend. While TV isn't line of sight, it resembles it in many respects. If you want a clean signal then you have to boost your antenna as high as possible. My brother and I put an antenna on a tall hill, the cable was around 300 feet, so we used inline amps to make up for cable losses, but he received several stations on every channel (the same channel) for around 6 states. To tune a station in he rotated the antenna.

    2. Antenna is critical. Nothing substitutes for a high gain highly directional antenna. If you have such an antenna the corollary is that you will need a rotor, to aim the antenna while watching the TV for optimal reception. The gain of the antenna is exactly like having a high gain amplifier, with none of the bad side effects.

    3. Coax also counts. Not all coax is created equal. RG6 is a low loss coax that is much better than RG58. You really need good coax, or any other effort is wasted. The shorter the coax the better, but altitude trumps coax length. Bad or cheap coax can distroy a good signal.

    If you have all of the above then a 20 db booster will help. Radio Shack used to make some good ones that resembled your schematic quite closely. There are also inline amps they used to sell to make up for coax losses, but if you push them too hard (too much gain too close) they will oscillate, which is very bad.

    Try describing your existing setup, and we can work from there.
     
  7. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Thank you Mr. Bill for your time:)

    I live in the Philippines were strong typhoons visit regularly.
    For this reason we can't make taller TV antenna.

    That's why I'm seeking for a high gain signal amp for TV because when typhoon arrives here in our country all lines are cut including power line & cable system.

    I made an Modified sine wave inverter for emergency power source to run our appliances as well as TV. But the aerial signal is weak because I'm only using the antenna of the TV itself.

    I think a Signal Amp. is the last sort.

    Please help me to build or modify this ckt to boost the aerial signal but w/ less noise...:)

    Thank you once again
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    What you are asking is not possible to do without spending a fortune.

    You might get 10dB or even 20dB of boost without the noise becoming unbearable.

    At 50dB gain, you will have nothing but highly amplified noise.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    Another gadget is collapsible antenna poles. They're poles of differing diameters that slide within each other with thumb wheel screws, you could fold it up before anything hits, though the antenna would still be just above the roof. It might be a good idea to rig quick disconnects so you could take the entire arrangement down, a good antenna isn't going to stand up to hurricane force winds well at all.

    The arrangement on the hill I was talking about earlier was less than 8 feet tall, and we still guy wired it, way below the tops of the trees. There the main concern was lightning, which we addressed pretty successfully (long term, who knows?). I used constriction clamps and three heavy duty car braided cables (made out of lead) to divert lightning around the rotor. I know it was hit several time, but the 3 foot spike driven into the ground the pole slipped over also did its job.

    A simple amp won't do what you want it to. You would almost have to build a tunable reciever and/or down convertor to do what you're trying to do, something I've never seen. The simple fixes are where to start before going to the advanced electronics (and the 50 db amp is advanced). If you just want to prove what we're saying is so then try linking one amp after the other. Bad results guaranteed.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I had the biggest and best TV antenna that was made in Canada high on a mast and with a rotor. I got many more stations than were listed in the TV Guide. I got a few stations in far away different directions but they were on the same channel.

    The antenna had a lot of gain. My TV had a lot of gain like most TVs do. An amplifier would not make any difference exept it would add noise.
     
  11. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Thank you Guys:)

    I think your right:rolleyes:

    I'll use the conventional aerial antenna instead.
    Do you know a better design for an aerial antenna to boost the signal a little bit:confused:

    ...........how about a Home-made CABLE SYSTEM????
    Do you think its possible:rolleyes:????

    Thanks
     
    Last edited: May 30, 2008
  12. SgtWookie

    Expert

    Jul 17, 2007
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    You might consider a satellite dish and a downconverter. Those are relatively small. I don't know if you can get them in the PI. I also don't know if the PI TV stations uplink to satellites.

    A homemade cable system would be rather challenging. If you had to run the cable signal for much of a distance, you would have to have amplifiers every so often to boost the signal back up to acceptable levels. In cable TV systems, they use a technique nicknamed "tilt", which means that the higher frequency signals are amplified more than lower frequency signals, as the coaxial cable attenuates the higher frequencies more than the lower frequencies. By the time the signal gets to the consumer, the "tilted" signal levels have equalized across the frequency spectrum. This isn't something that would be easy to build without some rather expensive equipment.
     
  13. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Thank you Sir for your reply:)

    I think it is more complicated:rolleyes: & expensive to have Cable TV system at home right??

    How about a shorter 'PASSIVE' aerial antenna but w/ better boost of signal???
    .....do you know an antenna w/ that design???

    Thank you once again.
     
  14. Gadget

    Distinguished Member

    Jan 10, 2006
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    You could stack 2 or 4 shorter aerials together to improve gain.
     
  15. bertus

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    Apr 5, 2008
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    Last edited: Dec 27, 2012
  16. Wendy

    Moderator

    Mar 24, 2008
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    Something else worth mentioning, it is a trick cable companies use. Built a tuned antenna for a specific station. By tuning the antenna you can make it extremely directional, and very high gain (antenna gain is the same thing as amplifier gain, only no power needed). You have to aim such an antenna exactly, and know where/what your going for, but it works well.
     
  17. thingmaker3

    Retired Moderator

    May 16, 2005
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    When I was a child, it was common to use a Yagi antenna to bring in TV stations from 40 or 50 km distant. Or more. They are stable in high winds.
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    The distance and obstrucions were not mentioned.
    Either the signal is too weak to be received or the TV's input is broken.
     
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