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Jottings on HEXFET power amplifiers

Hi all,
HEXFETs are quite popular with hams as HF linear stages . I too attempted to make some linear amps with them and that too with pretty promising results . Here is the outcome . The first FET that I tried was a IRF540 . The circuit used is given below .
I had to place some component in TINA as a choke , so I put a 1m choke . In reality , I used a torroid with some 20 winding . I could pull some 2~3W into a 50 ohm dummy load ( which I used as a termination in front of the CRO ) at 1MHz , but at higher freq , power output dropped drastically . The power calculation was carried on the basis of the voltage that I measured across 50 ohm load . The voltage peak to peak was 40V . So that gives me around 2W power . Next , I'm gonna try IRF530 , IRF610 etc  

Comments

  1. golden eagleAugust 24, 2015 at 10:45 PM

    Wow ! reinventing the wheel. I have many wheels look at my blog. You got 2watt at 50 ohm resistive load. Please not all the harmonics, subhoarmonics which were amplified, generated in the linear is deposited at the resistor and produce the heat... The voltage measured shows power very true but when we load the antenna, its not a pure resistive load. The filter can do two (?) functions. Remove harmonics, and make them sinusoidal ( no proof) and pass them to output port. So to get usable power we need to put filter which introduces the reactances and its all calculations... he he he...but this calculations might give big resistance......
    As such good experiments.. keep it up......

    ReplyDelete
    Replies
    1. Jishnu ThekkeppattuAugust 25, 2015 at 12:35 AM

      Thanks OM for the comments ! I'm happy that someone has taken time to go through the what I posted and give suggestions . I understand that I have not considered the harmonic problem . I will add a filter for 40m and make measurements . Besides I have the very popular IRF510 with me now !

      Delete
    2. Jishnu ThekkeppattuAugust 25, 2015 at 12:35 AM

      Please give a link to your blog :)

      Delete
  2. golden eagleAugust 24, 2015 at 10:46 PM

    * filter also does impedance matching. There are many online calculators as well as ARRL handbook gives the formulas....

    ReplyDelete

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