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The best NPN bipolar transistor for low NF at 435MHZ.

Discussion in 'Homebrew and Kit Projects' started by CO8TW, Mar 29, 2012.

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  1. CO8TW

    CO8TW Ham Member QRZ Page

    Hello Hams.

    Am looking for good NPN bipolar transistor to be used on 435 mhz in order to get a very low NF.

    Thanks in advance.

    Juan Carlos, CO8TW.
  2. AB9LZ

    AB9LZ Ham Member QRZ Page

    Does it need to be an NPN transistor? There are quite a few Mmic amplifiers out there that offer good performance along with a minimal parts count. The minicircuits web site has lots of good info.

    73 m/4
  3. K5UOS

    K5UOS Ham Member QRZ Page

  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    A FET may be a better choice but the 2n5109, 2n3866, 2sc1252 and 2sc1365 are all good transistors that will work in the UHF range.

    Sounds like you have a cool project brewing.

    Good Luck on your project.
  5. K7MEM

    K7MEM Ham Member QRZ Page

    Back in the days, when we were building MDS down converters for 2.1 GHz, we used the MRF901, MRF902, BFR90, and BFR91. We used mixers made with hot carrier diodes, but these transistors were used in RF Amp and Oscillator service. I am pretty sure they are all still available. The spec sheet for the MRF901 lists the nominal noise figure as 2 db at 1 GHz. All of the ones I mentioned work well with strip line.
  6. G0HZU

    G0HZU QRZ Member

    You really need to provide more info about your requirements for this device but for a general purpose small signal (low noise) amp at 435MHz the NEC 2SC3355 can be a good choice.

    It's a classic part that has been around for many years although I'm not sure about availability today. You can get them in SMD SOT-23 as the 2SC3356.

    The other classic low noise VHF/UHF transistor was the BFT66 but these are very expensive and hard to buy nowadays.

    The 2SC3356 is a pretty good device IMO.
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    I think that SMD would be the way to go, if a person is wanting a low noise figure.

    It would be nice to know the application.

    Prices very big time for all the transistors mentioned.
  8. KM1H

    KM1H Subscriber QRZ Page

    The 2N5109 was developed for CATV line amps when the maximum frequencies were 400-450MHz. It is extremely linear and rugged and with a heat sink and sufficient current it can handle big signals.

    Ive used them in broadband lossless feedback preamps, post mixer amps in transverters (used to replace useless MMICs in DEM transverters, and as Class A amps to boost low level 28 MHz transverter port output from HF rigs to useable levels. Havent blown one yet.

    Ive also used the MRF-901 and BFR91 at 432 and 440 decades ago.

  9. WA9SVD

    WA9SVD Ham Member QRZ Page

    The 2N5109 (or related series) is a good choice for low noise, and reasonable price. There are other, outlandishly priced bipolar devices available, but may not be suitable or necessary for your use. But also consider some of the FET's than can rival the bipolar devices for low noise. Each technology has it's own advantages and disadvantages.
  10. G0HZU

    G0HZU QRZ Member

    Note that the 2SC3356 has an equivalent part number of NE85633.

    According to the generic NE856xx datasheet the 85633 has a NFopt of 1.0dB at 500MHz with Vce 2.5V and Ic = 3mA.
    These parts are old devices and getting hard to source but were very cheap to buy. You can still get them for under $2.

    However, you could also check out the Agilent/Avago AT41511 and AT41533 devices as these give similar NF performance and there should be some decent models available for these parts as well. These NPN transistors can be bought for around $1.50.
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