new toy: cellphone signal extender

I bought one of these last week. It seems to work pretty well! The reception in the back office at DNA has always been crappy, but after running the antenna cable up to the 3rd floor, I reliably get 3+ bars instead of 1 bar or less. (There's 3 bars at the spot where the antenna is, just inside the corrugated steel roof. I really ought to punch through and put it outside, but I haven't yet.)

I wish it had more range on the other end. I wrote the manufacturer asking if it's possible to replace the base-unit antenna with a bigger one, but they haven't written back yet.

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19 Responses:

  1. skreidle says:

    Sure as hell can't afford one of my own, but I can see where an office/building would be able to make use of one or more nicely. :)

  2. mackys says:

    I wish it had more range on the other end. I wrote the manufacturer asking if it's possible to replace the base-unit antenna with a bigger one, but they haven't written back yet.

    It is, but it won't help as much as you think. I'm familiar with these things because I had to install one at my mom's way up in the mountains so she could get call phones. (Qwest quoted her $1700 to install a land line!)

    Besically, the biggest problem with these bi-directional amplifiers is that they run afoul of self-noise very easily. If the inside antenna generates a signal strong enough to be heard at the outside antenna, or vice-versa, you can start up a self-reinforcing feedback look that will A) render the device useless and in some cases B) even blow up the radio circuits inside. Most of the newer units made these days (including yours, I'm pretty sure) have self-limiting circuitry to prevent B though.

    If you're going to replace the inside antenna, I would recommend doing so with a panel antenna that has a large front/back ratio. In other words, it shoots most of the signal out one side and almost none out the other. Make sure the panel is oriented such that the non-radiating back side is pointing toward the outside antenna. That minimizes the amount of inside signal that makes it to the outside antenna. (Inevitably some will still get there, often by bouncing off stone and metal portions of the building structure. But try and keep it to a minimum.)

    For the ultimate in front/back ratio, I think you'll have to build your own biquad-hacked direct TV dish.

  3. fo0bar says:

    You paid how much for that? This would have been just as good:

    It works because I saw it on TV. And it's only $19.95.

    • gfish says:

      I wish I had a four foot antenna on my phone. Sigh.

      • killbox says:

        having antenna envy?

      • baconmonkey says:

        what, so you could pick up HAM radio signals on your cell?

      • Dipole antennas (commonly found on cell phones, TV's, radios) are tuned to a frequency by virtue of their length, which is why all cell phones that use a particular frequency (e.g., 800MHz or 1850MHz here in the US) have the same length antenna. A longer antenna would actually get you less signal, in other words.

        A directional antenna, or an antenna that had a bigger cross section would let you get more signal, OTOH.

        • mackys says:

          A longer antenna would actually get you less signal, in other words.

          Assuming you're talking about half-wave dipoles, that's a myth. The reason we use lambda / 2 dipoles is because it makes the antenna designer's job easier - the impedance of a half-wave dipole is very easy to calculate mathematically. But it's actually not an optimal length, in terms of signal:

          A lambda/2 is an antenna formed by two conductors whose total length is half the wave length. Note that from the electric standpoint, this is not a noteworthy length. As we will see, at this length the impedance of the dipole is neither maximal nor minimal. Impedance is not real but it does becomes real for a length of about 0.46 * lambda. The only outstanding property of this length is that mathematical formulas miraculously simplifies for this value.

  4. muftak says:

    Those things look very illegal.. you'll get the FCC or whoever it is after you.

  5. adolf says:

    The manufacturer won't help you with the problem because they'd trash the device's FCC certification, but you can always use a better (higher-gain) antenna if you don't mind forgetting about such things.

    The rule of thumb when it comes to antennas is that the more gain they offer, the more directional they are (law of conservation, and such).

    Even "omnidirectional" antennas suffer from these effects, as the radiation pattern flattens out while gain increases (think pancake instead of sphere). And you'll get the most gain from a directional antenna, where (somewhat like a horn-loaded loudspeaker) energy is not wasted by radiating in directions in which it is not useful.

    But from what I gather about DNA's floorplan, your office is in the corner of the building. This is good, because you'll be able to use a directional antenna and point it toward other useful areas.

    And, when you get into the game of high-gain antennas, it's important to make sure that they cover the frequency range that you're interested in, as they tend to be very narrow-band devices.

    Beyond that, it's all in the details of the antennas in question. Picking a good one, with the information I have at hand, would be like trying to answer "What's a good microphone for recording...stuff," so I'll astutely refuse to offer specific recommendations.

    Look to Tessco or Hyperlink Technology for easy-to-get the antennas and cabling, with Hyperlink being more likely to be able to match whatever strange connector that is installed on your amplifier. They've each got a $100 minimum, but at least Hyperlink's website has some real information.

  6. rudemech says:

    Those toys! Where does he get those wonderful toys!

    (Apologies if this has been done before . . .)

  7. tjcrowley says:

    I came back to this because I remembered it while cleaning out my office, and I found a book on different types of antennas buried in my stuff. I'm sure you could find the instructions online, but it occurs to me that if you just build a big honking j-pole antenna and use your normal coax, you could fulfill your bigger antenna wishes by nothing more than some copper piping, solder, and a mounting bracket.

    I have the exacts specs to cut the pipe based on the frequency involved, but from what I remember from my ham radio days the antenna shouldn't matter as long as it's tuned (read: made) for the frequencies and uses the same connector.