rf everywhere

Discussion in 'Misc Electronics' started by RichD, Mar 6, 2013.

  1. RichD

    RichD Guest

    Wireless is everywhere now, miniaturized to an astounding degree.

    Recently, I saw a report on a button size gardening
    gadget - stick it in the soil, it reports on moisture.
    Bluetooth earphones, etc.

    Who's designing these things? In my experience, RF
    designers are a rare breed, and with the digital market
    vastly larger, they're even rarer.

    I'll guess, the IC have been perfected to the no-brainer
    level. But still, you need need amps, filters, antenna, plus
    issues of noise and layout, yes/no? That stuff isn't obsoleted.

    I don't work in this area, but I'm curious, so can anyone
    elaborate on what's going on, from a system viewpoint?
    What are the chip functions, options, price, trade-offs?
    In which situations would you reject them, to roll your own?

    Is it simple on/off keying, or more sophisticated? Currently,
    in communications theory, sensor networks are a hot topic,
    where thousands of sensors are competing for bandwidth,
    but for mundane consumer apps, I doubt those issues arise.

    I'm looking to pick the brains of any gurus here -
     
    RichD, Mar 6, 2013
    #1
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  2. RichD

    Tim Williams Guest

    Hmmm, not a big deal I suspect.

    Build a general purpose RF block for, say, 2.45GHz BT or 802.11(etc), or
    whatever. Give it handles to talk with anything (modulations, bit
    streams, etc.), design and build it on a particular fab process, and like
    magic, anything incorporating that block will also work. Monolithic
    inductors can be fabricated with not very good Q at 2.45GHz (I think they
    usually peak around Q = 10 or 20 around 5GHz), but enough to do "silicon
    oscillators" and stuff. Voltage regulation (bandgap, or old school buried
    zener) and temperature compensation are no-brainers, as ICs go. Want a
    DDS? Just chuck some more IP at it! Then whatever ancillary function
    (moisture, temperature sensor, etc.) simply plugs into this mess of
    transistors and functions.

    Quite crazy, as all that circuitry is squeezing into a few milimeters of
    silicon, when a few decades ago it was, well of course it was migrating to
    thick film before monolithic, but before that, it was all machined
    cavities, hand-soldered RF transistors, and microstrip everywhere. I
    suppose Bluetooth would've taken up a whole rack, back in the 70s, and
    that's assuming the computing power to provide whatever spread spectrum,
    encoding, error detection, etc. functionality is required.

    Tim
     
    Tim Williams, Mar 7, 2013
    #2
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  3. You are right, but seems like someone has solved the RF problems once
    for each of the useful bands, then its a piece of cake to interface with
    sensors and one end and display/alarm at the other.

    For an example, the tyre pressure monitor systems at 433 MHz. 10 gram
    package, including battery, you screw on a tyre valve. Monitors tyre
    pressure and temperature for about 1-2 years of operation. Reports real
    time, every minute or so, to in-car readout.
     
    Adrian Jansen, Mar 7, 2013
    #3
  4. Frequently fails mechanically, causing loss of tire pressure, allows
    tire shops to charge for a "rebuild kit" whenever they swap a tire,
    requires a trip to the dealer (or specialized equipment/knowledge) to
    replace, even with an OEM replacement part.. other than that, they're
    just spiffy.


    Best regards,
    Spehro Pefhany
     
    Spehro Pefhany, Mar 7, 2013
    #4
  5. RichD

    Trevor Guest

    So pretty much like many of the new gadgets on modern cars, something else
    to go wrong that costs you money, even if you never wanted it in the first
    place :-(

    Trevor.
     
    Trevor, Mar 7, 2013
    #5
  6. years ago I was given a box of microwave "plumbing" from what may have
    been a broadcast engineer. The stuff would have worked with microwaves or
    hydraulic fluid. The guy who made the stuff seemed to be really good with
    a jewelers saw, copper pipe, brass discs rods and solder.
     
    Cydrome Leader, Mar 7, 2013
    #6
  7. RichD

    Guest

    I remember working on making bluetooth in a "single chip"
    we had a working radio and build an evolution of an existing SOC to
    stack
    on top of it in a single package

    Everything worked great when we tested the first samples, but then
    the
    software guys started running their code in ROM then the sensitivity
    dropped

    turned out that the ROM being in a different corner of the SOC coupled
    noise
    into the radio VCO inductors, but the RAM where the test code was run
    didn't

    I worked on one of the very first bluetooth implementations, it was;
    a DSP, a flash, an FPGA, an RF chip, a saw filter, a whole bunch of
    passives
    it was probably 5*5cm PCB fully packed on both sides

    -Lasse
     
    , Mar 7, 2013
    #7
  8. In the 1988 to 1990s ish time, there was a story in popular mechanics or
    popular science about a digital ghost canceler for television signals that
    bounced off buildings. It was huge PCB made using an array of DSPs and
    have to have pounds of gold plated ceramic chips on it. It was a pretty
    looking board, that must have screamed at like 16MHz or something like
    that.

    What would that take these days, to basically subtract patterns from a
    NTSC signal? A couple chips?
     
    Cydrome Leader, Mar 7, 2013
    #8
  9. Really I was commenting on the RF stuff. Certainly that seems to work
    as well as needed. Whether the rest of the design is as good as the RF
    section is a different kettle of fish.

    The aftermarket units using sensors like Tyredog seem to have a learning
    mode to accomodate sensor changes without special tools.

    Personally I would be happy if the system just warned that a tyre is
    going down, before it wrecks the tyre. Identifying which tyre is at
    fault is a secondary, and usually very easy, job.
     
    Adrian Jansen, Mar 7, 2013
    #9
  10. RichD

    MrTallyman Guest

    Not many folks making hard coax runs anymore.

    Semi-rigid and a few others abound.
     
    MrTallyman, Mar 9, 2013
    #10
  11. this stuff was pretty darn old.

    are there power levels where they stil use wavegides and the like?
     
    Cydrome Leader, Mar 10, 2013
    #11
  12. RichD

    Guest

    In countries still using analog TV, the UHF final amplifier is often
    implemented with klystron in the 100 kW range. The waveguide is quite
    large, due to the low frequency.

    DVB-T digital TV transmitters typically operate with only 1-10 kW,
    consisting of multiple redundant solid state modules, so there is not
    much need for waveguides any more.
     
    , Mar 10, 2013
    #12
  13. RichD

    Don Pearce Guest

    As much to do with frequency as power level. I've recently completed
    the design of a Ka band transceiver for satellite (30GHz uplink, 20GHz
    down). It is a domestic product for delivery of broadband to rural
    areas. All of the internal RF filtering is done in waveguide, as is
    the external combining of the transmit and receive signals into a
    single horn. The transmitter power is just 3W.

    d
     
    Don Pearce, Mar 10, 2013
    #13
  14. RichD

    Don Pearce Guest

    Andrew's Heliax is pretty low loss, and good for VHF and UHF runs.
    Dielectric amounts to nothing more than a thin spiral spacer - the
    rest is all air.

    d
     
    Don Pearce, Mar 10, 2013
    #14
  15. RichD

    Don Pearce Guest

    No, not at 10kW. At 100W or so it is fine. On a long run I would
    always opt for waveguide - tower dimensions permitting.

    d
     
    Don Pearce, Mar 10, 2013
    #15
  16. RichD

    T Guest

    Hardline! In essence it's a solid shield with a center conductor. That's
    enogh for RF into the 900MHz and 1.2GHz range.
     
    T, Mar 12, 2013
    #16
  17. what exciting things happens when you get moisture ingress?

    how hot can coax or waveguides run at high powers? I've never been by
    large transmitters, so the concept of anything but a power cord running
    warm is just strange to me.
     
    Cydrome Leader, Mar 12, 2013
    #17
  18. how does one terminate such cables? What sort of wiring goes on inside a
    giant transmitter or the antenna end of such a monster?
     
    Cydrome Leader, Mar 13, 2013
    #18
  19. RichD

    Guest

    In a coaxial cable the EM field propagates in the dielectric, not
    in/on the inner and/or outer conductor. The outer surface of the inner
    conductor and the inner surface of the outer conductor will just
    confine the EM field into the dielectric as does the inner surface of
    a waveguide.

    For this reason, the quality of the dielectric is critical, dry air is
    nearly as good as vacuum at lower frequencies (below a few hundred
    GHz).

    In addition, the metallic surfaces should have infinite conductivity,
    but of course, skin effect and oxidation will degrade the performance.

    The 15 cm coax is not very usable at frequencies well above 1 GHz,
    since the EM field starts to propagate in some strange waveguide mode
    above these frequencies.

    For lower frequencies, coaxal cables work OK even with much larger
    dimensions, such as 50 cm coaxial "cables" at a 500 kW short wave
    station.
     
    , Mar 15, 2013
    #19
  20. RichD

    Guest

    Coax has the fields contained within the cable, open-wire does not.
    Structures, people, and critters in proximity to coax don't matter.
    It's a different matter with open-wire. Open wire usually requires a
    BalUn, as well.
     
    , Mar 15, 2013
    #20
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