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Discussion in 'General Electronics Discussion' started by Jedimaster, Apr 26, 2012.

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  1. Jedimaster

    Jedimaster

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    Apr 26, 2012
    I have seen a post that bypasses the attenuator for the antenna to increase the range of transmission. I wanted to know how to do this with my current setup.

    Here are some photos for visual representation.

    [​IMG]

    [​IMG]

    [​IMG]
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    I suspect the guy posting that info doesnt really know what he is talking about.
    The inductor he is bypassing does NOT represent an attenuator. without seeing an actual circuit for the unit, I would have to guess that its either in series with the existing antenna and providing some base loading so the existing antenna can be shorter than normally needed OR its in a DC supply path to the output trasnsistor of the transmitter.
    I suspect its more likely the first option.

    Dave
     
  3. Jedimaster

    Jedimaster

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    Apr 26, 2012
    So does that mean it can't be done? I am an IT guy not an electronic engineer. I have taken some soldering courses and have done some circuit repair, but I'm afraid I know little else. If I should give up let me know; however if there is a way to do this I would like to try it.
     
    Last edited: Apr 26, 2012
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    well it just seems a little oddball, seems many of the responders noticed no difference. And maybe those few that did, happened to use a longer length of wire as their antenna ??

    in the long run if its working ok dont mess with it... there's an old saying ...
    "if it aint broke - dont fix it"

    if you dont care if you damage the unit, maybe beyond repair, then by all means have a play and see what happens :) I have no idea what they are worth to replace

    Dave
     
  5. Jedimaster

    Jedimaster

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    Apr 26, 2012
    This unit is an old one, and you can hear static when the device is less than a meter from the receiver antenna. I used an RP-SMA connecter to couple it to an old rubber ducky antenna. This tripled the range and clarity of the unit. However I would like to boost it as much as possible just for fun ;)
     
  6. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    The RF output of the BH1417F is pin 11. On the Belkin Tunecast and Tunecast II transmitters, there is a T or pi attenuator network and a small base load inductor. The antenna is a short length of wire alongside the input pigtail. These things were done to make the output so weak that adjacent transmitters just a few feet apart couldn't interfere with each other and to comply with FCC output power limits. Your pictures are upside down and too unclear to see the attenuator components but they are substantially similar to the ones shown in figure 10 on page 15 of the datasheet.

    http://www.crowcroft.net/kitsrus/bh1417f.pdf

    You can remove the attenuator components and the base load inductor and install a jumper to the existing antenna but it's easier to remove just the first series resistor connected to pin 11 and attach your antenna line to pin 11 through a coupling capacitor. Use a regular FM whip antenna (28").

    The Belkins also run the IC at a lower than optimal voltage when using internal batteries. The IC can operate from 5V. Try using the externally connected power and see what voltage is being applied to pin 8 (Vcc).

    Test your range. Don't interfere with reception of licensed transmitters.
     
    Last edited: Apr 26, 2012
  7. Jedimaster

    Jedimaster

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    Apr 26, 2012
    Thanks this is exactly what I was looking for. Will I need to use a whip antenna, or will this little one I'm using now work? I don't want to extend the range too much, so I will keep the two AAA cells in it for now. Unless that isn't enough power to get a range of 10' or so. I don't plan on stepping over the channel completely just enough to remove the static.
     
  8. KJ6EAD

    KJ6EAD

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    159
    Aug 13, 2011
    Being an IT guy, I guess the antenna you're using is made for WiFi (2.4GHz) so it's electrical length is quite a bit shorter than what's optimal for the FM broadcast band, but as long as you're aware that the antenna itself can attenuate your signal, carry on.
     
  9. pioneer31

    pioneer31

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    0
    Jul 15, 2012
    I have modified my Tunecast II by attaching a wire dipole, using an extended audio lead as the ground and a corresponding antenna of the correct length

    However I'd like to remove the attenuator network if possible. Can you tell me what happens if I solder the antenna to pin 11 WITHOUT a coupling capacitor?

    Does anyone know 'how much' the attenuation is? Am I going to notice any difference, having already performed the antenna mod?
     
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