Search This Blog

Friday, 31 January 2014

JBoT - A linear for Minima

Well,

In an attempt to finish up my Minima tranciever, I have today been making the linear amplifier to follow the gubbins we have so far.

The Author has used this:

http://www.hfsignals.org/index.php/File:Qrp-linear.png

and I saw no reason not to follow suit.

Here's what the linear looks like right now:


Mine is built with 2N3053s (because I had some). I had a spot of bother getting the correct output from T2, this should produce 2 equal amplitude but out of phase signals. I eventually managed to make something that seemed to work, the output of T2 looks like this:


and the output of the final transformer after the 4 finals looks like this into a dummy load:


So, I make 56V peak to peak about 7.8 watts, so I suspect I am driving the amplifier a bit hard with my sig gen and attenuator set up. I also think I have a bit of a tendency for the finals to oscillate.

So, we will have to see. The next bit I need to do is understand the band selection outputs from the Minima software - I am sure these are designed to allow me to switch LPFs after the linear, which I need to do as the linear will have to be followed by suitable filters to remove any harmonic content.

Good progress though, egh?  

2 comments:

  1. I too am wondering about the LPF's and how they are selected and how many to have as well... I suspect that the code doesn't do that yet. May have to add a shift register and some code to select the correct LPF.
    I'm still at the pondering stage..

    ReplyDelete
  2. I have really enjoyed following along with your build. Great work!! Helps to put some "flesh" on the bones of just reading about it and following the mail list.
    KB9JLO

    ReplyDelete