Amplify digital tv antenna signal with class A amplifier possible?

Discussion in 'General Electronics Chat' started by circuitfreak2000, Apr 7, 2015.

  1. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    Would it be possible to boost the signal from an aerial antenna with a simple class A amplifier circuit to get a stronger digital tv reception?

    With something similar to this:

    [​IMG]
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I don't see much hope for that circuit being useful, since it contains no meaningful details. What frequency band(s) do you think are occupied by digital television channels?
     
  3. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    I believe around 600 Mhz
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Antenna amps are very inexpensive. Why build one?
     
  5. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    It's more fun ;)
     
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  6. #12

    Expert

    Nov 30, 2010
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    OK. You are risking about $2 worth of parts. Build it and tell us how it turned out.
     
  7. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    I tried already with a BC547 and a N2222 NPN transistor, but I think they cannot handle the frequency. I didn't see any improvement in the signal strength. Perhaps this would only work for analog tv channels and not digital tv?
     
  8. Reloadron

    Active Member

    Jan 15, 2015
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    It may be fun but building even a 600 MHz pre amplifier is a pretty good technical challenge, right down to not just the components but how the board is constructed and components spaced. This is likely why even experienced RF engineers more often choose to buy over build. Next the antenna and feed line are everything too. High end RG6 (75 Ohm) coax is preferred with a good high quality high gain antenna on a good rotor system. There is much more to this than the simple common transistor amplifier you posted.

    Ron
     
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  9. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    I understand, but my thought was that a class A is a broadband amplifier and perhaps with the right transistor it could actually work.
     
  10. Reloadron

    Active Member

    Jan 15, 2015
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    Well I certainly agree you have nothing to lose by trying. During my formative years, long, long ago I did discover that even a blind squirrel finds an occasional acorn. :) Additionally you should come away having learned a few things so by all means continue to march.

    Ron
     
  11. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    I want to clarify that this device I try to build goes between the coaxial antenna cable and the tv antenna in-plug. It's not an RF circuit, so it shouldn't be too complicated nor require special metal housing, etc. Please correct me if I'm wrong. As far as I have learned, a class a amplifier does not change the frequency. It only boosts the signal amplitude.
     
    Last edited: Apr 7, 2015
  12. #12

    Expert

    Nov 30, 2010
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    Absolutely wrong.
    This is like saying, "If I scrape the flash powder out of my firecrackers, will it make my SR-71 spy plane go faster".
     
  13. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    What I meant to say its not a sophisticated receiver / transmitter RF circuit. Just a transistor boosting the current.
     
  14. Papabravo

    Expert

    Feb 24, 2006
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    I'd be surprised if you get any signal at all through such a device made from general purpose transistors. It just doesn't work the way you think.
     
  15. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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  16. Papabravo

    Expert

    Feb 24, 2006
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    VHF television signals can mean 54-88 MHz., which is a far cry from 600 MHz.
    I can't find any evidence that you can buy one.
    Wait, I see it on a list. Still can't find a datasheet.
    Found it:
    http://www.onsemi.com/pub_link/Collateral/MPS918-D.PDF
    Typical GainBandwidth Product is 600 MHz. which means you can get a gain of 1 at 600 MHz. The max is 1500 MHz. So if you buy a bin full you might get one that will give you some gain of 2 or 3 at those frequencies. Pretty tough to make it work there. Certainly those capacitor values will be too big.
    BTW do you have any test equipment to let you know it is working?
     
    Last edited: Apr 7, 2015
  17. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    Somebody just mentioned to me that digital tv is now UHF and not VHF and requires microwave technology. He seems to be savy as he said he built a VHF antenna amplifier circuit before.
     
  18. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    The transistor in the datasheet matches the 2N3563 in the circuit diagram I posted. It looks like this one can handle the required Mhz for digital tv. The BF198 only seems to handle 400 Mhz. The BC547 I tried can only do 300 Mhz. I suppose if I use a 2N3563 the signal should be at least equal or slightly boosted.

    If a BC547 can do 300Mhz, wouldn't it also work in the VHF amp circuit I posted?
     
    Last edited: Apr 7, 2015
  19. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    As mentioned, you just can't cobble together a UHF preamp with RF building experience. Best bet is to buy a UHF preamp. Channel Master makes some pretty good ones.

    I don't use a preamp as nothing beats a good UHF antenna mounted and pointed properly. Try www.tvfool.com to see what you can expect to get on OTA from your location.
     
  20. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
    39
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    Last edited: Apr 7, 2015
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