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Wanted: an RF Switch

Discussion in 'Electronic Design' started by garyr, Apr 16, 2013.

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  1. garyr

    garyr Guest

    I'm trying to build a 80/40 meter receiver and I'd like to be able to
    switch the RF input between the two bandpass filters. This sort of thing is
    usually done with relays but I'd like to avoid that if possible. A
    SN74CBT3306 would be ideal but I think the on-resistance would be too high,
    thought it's hard to tell from the data sheet. The impedance of the signal
    path is 50 ohms. I think I have a way to do it using 2N7002's but it
    requires a lot of parts. Is there a device similar to the 3306 that might be
    useable for this application?

    The input and output capacitors of the double-tuned filters are 2200 & 2700
    pF so the stray capacitance of the switching circuitry would not affect the
    response very much.

    Thanks in advance
  2. Guest

  3. garyr

    garyr Guest

    I posted my query before doing enough searching and have since found the
    TS5A3160 which looks like it will do the job.

    Thanks for your replies.
  4. miso

    miso Guest

    RF is AC, so can't you use a simple diode switch and AC couple? That is
    how they do it in radios for years.

    Otherwise, for a one-off, RF relays are not that expensive.
  5. Tauno Voipio

    Tauno Voipio Guest

    The solution used by equipment manufacturers for decades is
    a bunch of diode switches. 3.5 and 7 MHz are not considered
    worth RF cmponents in the current regard.

    The simplest solution uses one series diode switch at each
    filter end (4 total), and you can use more for better isolation,
    e.g. a 3 diode T switch instead of just a single series diode.

    For examples, get te ARRL handbook and read the chapters on
    receiver design.
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