General-Purpose and RF JFET and MOSFET

  1. Hey guys,
    I'm looking for some general-purpose N-channel JFET and/or MOSFET transistors (depletion-zone) to be used as audio frequency and radio frequency amplifiers (although probably not higher than 50 MHz). They likely won't be subject to voltages over 12 volts or current higher than 200 milliampers. I've tried searching mouser and google but all I seem to be able to find are power MOSFETs. You guys know of any that would be work?

    Thanks
     
  2. jcsd
  3. vk6kro

    vk6kro 4,059
    Science Advisor

    BF981 dual gate Mosfets seem to still be readily available on EBay. They cost as little as $1 each if you buy 5 or 10.

    These work well to above 200 MHz as low noise amplifiers or mixers.

    There are plenty of circuits on Internet using this device.

    They do have a low output impedance, so circuits that put a parallel tuned circuit directly across the output of these devices should be treated with suspicion. Such circuits will be severely damped by the low output impedance.
    The output of the BF981 should be connected to a tap on the coil of a tuned circuit.

    Currents of 10 or 20 mA are typically used with these FETs.
     
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  4. Baluncore

    Baluncore 2,875
    Science Advisor

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  5. davenn

    davenn 3,813
    Science Advisor
    Gold Member
    2014 Award

    the J309 and J310 are also a great small signal FET's
    have used in many receiver projects

    dunno if you could push them to 200mA tho, without looking at the datasheet

    To the OP, you haven't really stated what you want these FET's for ??

    receiving or transmitting ??

    The IRF510 is a popular FET device for use in 1 -50Hz for a transmitter
    there's dozens of sample circuits on google
    single device will give you ~ 10W and there are example circuits of ones used in parallel


    Dave
     
    Last edited: Jul 9, 2014
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  6. It's for a project that requires me to send and receive an FM signal at about 50 MHz. I was planning on using FET transistors for all the low powered oscillation, mixing, and amplifying stages, and possibly the transmitter output and audio output stages. The transmitter doesn't have to be very powerful, in fact, for it to work as a class 15 device it has to have a range of less than 200 feet, so I'm aiming for a low-powered transmitter in the milliwatt range. The audio output should be powerful enough to drive earphone speakers, but for that I could use a BPJ buffer.
     
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