Friday, 11 June 2010

1.3 GHz Driver amp

As promised here is a picture of the 1.3 GHz driver amplifier I
have been working on. It is based on a FPD4000AF pHEMT
which I bought on eBay for about 1 pound. The device is rated at
4 watts and is good to 4 GHz. I am no RF guru so I was not expecting
much. It has about 8db gain at 1.3 GHz slightly more at the bottom
end of the band. It should have > 10 db gain at these frequencies.
It looks like the input match is not quite right. But it is stable so
that is a start.

Update. With a slight change to the input circuit I am now getting
13 dB gain @ 1.3 GHz and the gain across the band is flat within
1.5 dBs. Because of the long leads and low output of the WBX I
don't have enough to drive the PA beyond 100 mW output at the


  1. Hi, I consult that software used you to design matching networks in and out, because I've used Smith Software and I did not get results, I only get 6dB gain @1300MHz.

  2. Hello Josue,
    I used Puff to design the matching networks. I started with the manufacturers application note loaded the values into Puff then scaled everything for the lower frequency, then modified the values until I got the expected gain and match. I then had to modify the actual circuit to reproduce the 'ideal' results predicted by Puff. The gain was measured using a Gigatronics power meter. The input return loss was not as good as I had hoped but it should be good enough.

  3. Hi Charles,

    I also have some of these transistors, but I am struggling to find the dimensions for the original demo board, do you still have details?


    1. Hello James,

      I did a quick search of my backups and found the
      details of the 3.5 GHz evaluation board if that
      is of any help? I probably have other files as
      well but I would have to search a bit harder for

      If you give me a way of emailing you I can send
      you what I have.


    2. james (at) digital (hyphen) light (dot co dot uk)

      Many Thanks,