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RF Signal Levels

Discussion in 'Electronic Repair' started by mcp6453, Nov 25, 2007.

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  1. mcp6453

    mcp6453 Guest

    Does anyone make a simple RF signal (TV bands) level meter suitable for
    home use? The ones I've seen are multi hundreds of dollars. I'm going to
    redo my video distribution network in my home, and I'd like to know that
    I have the correct signal level at each tap.

    My cable company does not provide consistent signal level, either. It
    would be helpful to check up on them frequently.
     
  2. JANA

    JANA Guest

    An RF meter is not a simple device to build. The frequencies are very high,
    and component assembly and selection is very critical. There are good
    reasons why RF meters are expensive.

    Your best test is to wire everything up, and see if the pictures are okay.
    If they are all clean, you know that they are okay.

    --

    JANA
    _____


    Does anyone make a simple RF signal (TV bands) level meter suitable for
    home use? The ones I've seen are multi hundreds of dollars. I'm going to
    redo my video distribution network in my home, and I'd like to know that
    I have the correct signal level at each tap.

    My cable company does not provide consistent signal level, either. It
    would be helpful to check up on them frequently.
     
  3. N Cook

    N Cook Guest

    I don't know if this will work, but I would start with a tuner out of a TV
    or VCR .
    Either one that is working order , as original, so you can check powered,
    which is supply pins, IF pins etc before removing or one with known pinning.
    You would need a supply of about 35V probably.
    Rectify the IF picture signal output and there may be enough signal to show
    on a 50uV analogue meter or DVM.
    For comparative rf strengths, which is all you need.
    Others on here here would know if it was possible, its just how I would try
    first.
    There may not be a linear correspondence between UHF signal levels and IF
    levels. for each signal
     
  4. Meat Plow

    Meat Plow Guest

    I own a Digisat signal strength meter for Direct TV dishes. It was about
    $150 USD. I suppose its construction matches or exceeds the
    construction criteria for any TV signal meter. I think if the OP searches
    well enough he'll come up with something in the price bracket.
     

  5. The cheapest I've seen a new TV field strength meter was over $300
    and that was 30 years ago. It was a Sadelco analog FSM for VHF & UHF
    TV.

    http://www.tequipment.net/SadelcoPriceList.html for new Sadelco meters

    <http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=sadelco&category0=>
    for used, starting at $100.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  6. Jamie

    Jamie Guest

    Our cable company around here intentionally varied the signal level to
    disrupt the off market cable descramblers. Most of them required the
    use of an outboard cable box converter which didn't handle signal
    strength changes to well. On top of that, they varied the frequency
    slowly. THis also caused issues . it was a deterrent. From what I
    understand it worked nicely.
    Their own units handled freq shift and signal level changes of what
    they were doing just fine.

    I always thought each distribution point on the cable center used
    an AGC output to maintain a fixed level of output on the average but
    after talking to a long time friend that is a tech in our local center
    , he verified that is not so and it makes it easy for them to perform
    this practice..

    Now we have digital cable :)

    I'm sure your case is not this, most area's I know of are now on a
    digital system.

    For accurate calibration, you really need an Analyzer to cover the
    whole spectrum if you have a system that has gain settings for different
    frequency windows.
     
  7. Charles

    Charles Guest


    As JANA posted, use a portable tv and simply go from tap to tap. Weak
    signals produce a snowy picture with NTSC signals and nothing with ATSC
    signals.
     
  8. Google for SENCORE and also check E-bay for one of their older analog
    units. Should be good enough for home use.

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  9. If that is true, then the FCC would shut them down. The anual 'Proof
    of performance" required of EVERY CATV system has to be on file, and if
    it doesn't meed the technical standards, the system can lose their
    franchise. if the levels are changing you probably have a bad drop, or
    the tap is bad.


    Bullshit. The modulation scheme for a lot of analog scrambling
    changed the DC reference for the video. The use of non standard video
    caused the changing levels,

    Why should a cable compnay do ANYTHING to help you be a theif?


    A specrium anaylzer, or a sweep system is used for proof of
    perfomance. A calibrarted FSM is used for measuring signal level on a
    per channel basis. BTDT for United Video. I ran their service center in
    Cincinnati for four years.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  10. Mr. Land

    Mr. Land Guest

    Are you looking for absolute DB readings or just comparative signal
    quality levels?

    How about the following?

    Pick up an RF attenuator box (should be fairly inexpensive).
    Hook it's output up to the most portable TV you've got. Connect the
    att. input to a point
    where you know you've got good signal. Crank the attenuator all the
    way
    off (no attenuation) and tune in a channel on the TV. Then gradually
    attenuate the signal
    to a point where you would consider it unacceptable (totally
    subjective call.)

    Then cart the attenuator-TV combo around and use it to "measure" what
    you're getting
    at various points in your distribution wiring. You might even be able
    to twiddle and mark
    the attenuator knob at various positions to make comparisons.

    I have an attenuator but I've never tried this - you might find the
    knob hard to adjust, perhaps
    due to any AGC circuitry in the TV.

    It would probably be nowhere near as accurate as a real meter, but
    it'd give you some
    data at least, which is better than none at all.

    If you do try this, I'd like to hear how it went.

    Cheers.
     
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