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RF transceiver chips with low-kHz bandwidth?

Discussion in 'Electronic Design' started by Joerg, Dec 2, 2010.

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  1. Joerg

    Joerg Guest

    Hi Guys,

    Looking for a transceiver chip with low IF bandwidth, sub-1GHz. All the
    usual suspects I have canvassed can't be set below about 50kHz
    bandwidth. This leads to a poor link budget for very small data rates
    and we'd only need a few bits per second. Modules are too expensive, got
    to stay under $3 for chip plus surrounding parts, in k-quantities. Any

    Reason is we need lots of range, >1000ft if possible with stub antennas
    and ideally no more than 10mW because that's the limit in many
    countries. With that requirement 2.45GHz is pretty much out,
    unfortunately. Of course I can roll my own analog version but a chip
    would be so nice. Something with a kHz BW or so, that has the smarts to
    see-saw across a range so it can catch a carrier without needing
    super-stable oscillators and such. I can do the see-saw scans with a uC
    if needed.

    Oh, and we'd need something from a reputable supplier that can actually
    supply. Know what I mean ... :)
  2. Hi Joerg,

    Look for the ADF7021-N from our dear friends Analog Device... IF bandwidth
    down to 9KHz, 2,88$.

    Friendly yours,
    Robert Lacoste
  3. Joerg

    Joerg Guest

    Merci beaucoup, Robert. It won't get to the single digit kilohertzes but
    does go down to 12.5kHz. That's a lot better than all the others with
    50kHz. The price is a bit high and it has a stiff package which isn't so
    great if gear gets banged around but it sure beats all the other chips
    in performance so far.
  4. No, sorry, we used it only for FSK
  5. Joerg

    Joerg Guest

    Robert, what kind of range did you get with it? And what sort of antenna
  6. Well, we used an ADF7021-N for a VHF system (169MHz telemetry band), so
    range was, well, long (around 20km open field, some km in urban
    environments), so I guess this experience will not be transposable to
    yours... By we way we wrote a small white paper on advantages of 169Mhz for
    telemetry, in case someone is interested :

  7. Jon Kirwan

    Jon Kirwan Guest

    Thanks. I've been following the discussions in this thread
    and learning from them. The paper connected some things I
    learned about elsewhere (Friis formula, though in somewhat
    different form from eetimes and mpdigest in 2007 authored by
    ADI employees) and anticipated would come up in your paper as
    I read it. And they did! The worked details were nice, too.

  8. Joerg

    Joerg Guest

    Excellent paper, Robert. Unfortunately we can't do 500mW. Well, on
    900MHz and inside the US we can and sometime do but that won't fly at
    all in Europe. Especially not in France ;-)

    I like VHF just like you do, much better for longer range
    communications. That is why I completely fail to understand why many of
    our TV stations gave up their VHF channel for a UHF channel, without
    putting up a fight.
  9. Joerg

    Joerg Guest

    They don't let you. I guess that designing external filters is expecting
    too much these days so they poured it into the silicon. Or maybe
    engineers just don't want to fuss around with this and rather treat it
    as a digital building block. Probably for the same reason many people
    won't or can't drive a stick shift anymore.

    It's like with TV set, things are being dumbed down. Heck, ours won't
    even let you add channels. You can only run a clean slate scan and there
    are few days when more than 95% of channels will "stick".
  10. Rich Grise

    Rich Grise Guest

    You should run the channel scan after dark - propagation conditions are
    much better then. :)

  11. Joerg

    Joerg Guest

    Not out here. We even stopped taping movies if they do not run during
    the day. After 7:00pm numerous channels begin to pixelate. Sometimes we
    were sure a movie stuck, only to discover that it froze into a Picasso
    painting 1h into the movie #@&*!!

    Our TV consumption has dropped significantly since DTV was foisted upon
    our nation. Same for many neighbors. Analog was better, much better.
    OTOH it had some good effects, more real socializing among neighbors.
  12. Joerg

    Joerg Guest

    Unless a slew of little meteorites hisses out up there :)
  13. Rich Grise

    Rich Grise Guest

    Maybe it's just here then. During the day, channel 50.x doesn't come in
    worth beans, but at night it's about the strongest one in the range.

    How about tropospheric bending by the thermocline? :)

  14. Joerg

    Joerg Guest

    Maybe it's the smog?

    DTV reception quality does not have much to do with field strength. The
    ATSC protocol appear to be so shakey that the slightest multipath
    reflection can toss it off the rocker. Sometimes when my wife says that
    we probably can't watch or tape anything because the stations all
    blue-screen I look at the spectrum in my lab. And sure enough, they're
    all there, nice and strong. But undecipherable :-(
  15. Ah, the Friss formula for free space path loss, which states
    bluntly that this path loss is proportional to frequency...
    If that were true, then light wouldn't ever get anywhere, now
    would it?

    Of course, free space path loss simply goes as r^2. No frequency
    term in there. No one ever seems to notice that Friss defines
    his effective antenna apertures as a fixed number of wavelengths!
    In fact, he's supposing smaller and smaller antennas as the
    frequency goes up. No wonder the amount of received power

    Jeroen Belleman
  16. Charlie E.

    Charlie E. Guest

    No, it is because OTA transmissions don't bring in any money, while
    cable and sattelite rebroadcast does. You just need to broadcast
    anywhere to get the rebroadcasters to give you money...

  17. Joerg

    Joerg Guest

    That's what staion owners think but they are missing part of the
    picture. And so so chief engineers. I talk to one whose station lost a
    chunk of coverage when they gave up VHF. His argument was that UHF does
    penetrate buildings better. Ahm ... they've all got cable down there in
    the city.

    The folks with more disposable income, a.k.a. prime targets for ad
    revenue, do not live there. They live in the suburbs. Many purposely do
    not have satellite of cable because they don't want the TV to dominate
    family life. But they do watch the news, or used to. That's where
    reception became unreliable. So what do those people do? They upgrade
    their Internet for more megabytes/sec, watch the news there, and
    subscribe to Netflix. Viewer numbers for stations shrink, ad revenue
    shrivels up, personnel costs need to be reigned in. Some of the latter
    is clearly noticeable by now.
  18. Charlie E.

    Charlie E. Guest

    Yes, and this used to matter for ad prices and such, but now that the
    majority of viewers are on cable/sat, the stations don't care as much
    anymore... :-(

  19. Joerg

    Joerg Guest

    You'd be surprised how many people out here are not on sat/cable. And
    those tend to be the ones with well-paying jobs, meaning disposable income.

    However, there is a trend that the media moguls seem not to grasp and
    this one is much more serious: The kids of those folks. Once they head
    off to college many forego TV altogether. Internet and Netflix is all
    the rage there. I know several who don't even have a TV anymore, they
    watch everything via their computers.
  20. josephkk

    josephkk Guest

    Thread read. Just the same, can you add (modulate with) some nice
    predicable PRN thus using the extra bandwidth to your advantage?
    Regulatory issues may make hash of this idea.
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