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Distance of remote

Discussion in 'Electronic Design' started by Jon Slaughter, Apr 24, 2007.

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  1. I have a remote to a tv that I would like to increase its distance by a few
    feet. The system is Dish TV and the remote uses UHF. I have taken apart the
    remote and it uses

    http://www.analog.com/UploadedFiles/Data_Sheets/ADF7901.pdf.

    Unfortunately its SMT so its going to be hard to mess with. I need to know
    exactly what I can modify to increase the range from about 50ft to about
    55ft. I don't even know if this is possible though.

    I figured that if I increased the current through the antenna that it could
    give it enough.

    Whats strange is that having the remote at very specific points and at very
    specific angles in the room will get the signal to the reciever. I do not
    believe this is due to reflections or anything like that. Maybe the signal
    is degraded by the long distance so much that it only works 1/100 of the
    time? It has steadily gotten worse over time and I assume its cause of the
    batteries.

    In any case I'm wondering what you guys think I can do? Maybe run a few more
    batteries in it? Increase the loops of the antenna? Change the power going
    to the transmitter section?

    I'm going to read over the datasheet and see what I can come up with.
    Unfortunately I do not think there is going to be a simple of a solution as
    I initially thought.

    Thanks,
    Jon
     
  2. On the datasheet page 1 I have located the RFout side and I was wondering
    what is the inductor for? Remove RF noise from VDD? and will increasing VDD
    increase the range?

    Thanks,
    Jon
     
  3. The antenna (especially on the receiving end) is probably
    the easiest thing to monkey with.
     
  4. My guess is that it provides DC supply current to the output
    stage.
     
  5. The output stage is the antenna? There is a dc blocking cap for obvious
    reasons. It would seem that if I increased the RF VDD that it would supply
    more current to the antenna and therefor increase the power dissipated by
    the antenna which should increase the distance?
     
  6. Not sure. Depends on what they use on the recieving end. If it was simply an
    op amp or something then possibly but seeing they use SMT I'd still have
    trouble. Also it would increase the noise and if thats the original issue
    it wouldn't help much?

    Thanks,
    Jon
     
  7. john jardine

    john jardine Guest

    The inductor XL is 50ohms at 350MHz and is used in preference to a load
    resistor. Idea is that the PA stage can develop an A.C. signal voltage
    across the inductor of nearly twice the supply rail voltage. Hence 4 times
    the possible RF power out, as compared to a 50ohm resistor.
     
  8. BTW,

    "The FSK_ADJ and ASK_ADJ resistors can be adjusted in the

    system to optimize output power for each modulation scheme.

    An additional 1.5 dB of output power is provided for the lower

    bank of channels to adjust for antenna performance. The CE

    line allows the transmitter to be powered down completely.

    In this mode, the leakage current is typically 0.1 µA."



    Which would seem to imply that I could easily change the power... except
    probably they are using the maximum anyways.
     
  9. Gary Tait

    Gary Tait Guest

    I'd play with the receive antenna first.
     

  10. Ok, looking at the circuit it seems they use



    "15 RSET_OOK The value of this resistor sets the output power for data = 1
    in OOK mode. A resistor of 3.6 kO provides the maximum output power.
    Increasing the resistor reduces the power and the current consumption. A
    lower resistor value than 3.6 kO can be used to increase the power to a
    maximum of 14 dBm. The PA does not operate efficiently in this mode.

    16 RSET_FSK The value of this resistor sets the output power in FSK mode. A
    resistor of 3.6 kO provides maximum output power. Increasing the resistor
    reduces the power and the current consumption. A resistor value lower than
    3.6 kO can be used to increase the power to a maximum of 14 dBm. The PA does
    not operate efficiently in this mode."



    A value of 3600 ohms for pin 16 and 5*10^8 for pin 15. So it looks I cannot
    adjust the power any better. I assume the OOK mode isn't used and this would
    explain the high resistor value unless I'm misreading it. (says 548 on it I
    think)
     
  11. I'm going to try and decrease the resistance of the 3.6kohms. IT says the PA
    doesnt' work well but maybe it will give me enough.
     
  12. Ok guys, nm. Got it to work(atleast it looks like it). Paralleled a 10k
    resistor with the 3.6k and it seemed to increase the power a bit more.
    Works about 80-90% of the time instead of about 1-10% of the time. Might be
    able to go a little lower but its good enough for now.

    Jon
     
  13. Steve

    Steve Guest

    Are you saying it works reliably at 50 feet and hardly works at all at 55
    ft? If so, then the math says adding less than 1 dB to the total RF power is
    all you need. But I doubt that would be sufficient - the drop-off seems too
    steep. I'd pay more attention to your other data that says specific
    locations in the room are better than others. Sounds like multipath or a
    local interference issue. How did you conclude its not due to reflections?
    Have you tried moving the receiver around a bit (like a quarter wavelength)?
    It might be easier than changing the circuitry if you only need it to work
    in one seating location.

    I've found certain rechargeable appliances can create havoc in the UHF
    region for distances of 10 feet or so.- any battery chargers in the vicinity
    (cordless vac, for instance)? Check opposite sides of adjoining walls too.

    Steve
     
  14. Well, I already fixed it last night and now its about 99% reliable. I do not
    know if what I did is exceptable but it is working much better(for now).

    Now if it was reflections I would still have the same issue but it
    completely gone away. It was just out of its range for the power it was
    using. Increasing the power increased the range. Was an easy fix but took
    some time to figure out how to do it. Luckily the chip had the ability to
    increase the power over its optimal setting and that the remote did not
    already do that. It was simple as soldering in a resistor which was actually
    kinda hard since I had to solder in an axial resistor onto a SMT resistor.
    Wasn't to bad though.

    I'm mainly worried about the long term effects of increasing the power. The
    datasheet does not discuss the consequences. I'm not sure if it will just
    drain the battery faster or if it could decrease the life of the circuit.
     
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