Sunday, February 8, 2015

KD1JV PFR-3 transmitter

I always wanted to try making making a cw transmitter like the one in KD1JV's PFR-3. It looks so simple. Steve uses the square wave comparator output of the AD9834 into an *74HC02 quad nand gate to buffer the output into 3 paralled BS170's. Since the Si5351 already puts out a square wave - why not? A quick test gave me 4 watts into a dummy load. I added a 40M LPF because I plan to lash this up with an already built CRX1 since it has some nice built-in conveniences, like TX/RX switching, muting and a nice twin-T sidetone oscillator.
Spectral plot of output.

Below is the finished product.


Front Panel

Etherkit Si5351 breakout board
Close-up of transmitter


  1. Do you have a schematic of just this showing Si5351 inputs and keying inputs?

  2. Hi Michael,
    The schematic is referenced in the text. It is not mine to reproduce. The only thing that I didn't include in the photo is the keying part. Steve uses an FQPF7P06 that handles the current to the BS170's and as you can see, it is turned on by a 2N7000 keyed by the microprocessor. My thinking was that I could skip those parts and key by turning on or off the output of the Si5351 while leaving +12V on the BS170's. I don't think Steve is able to that with the output he is using on the AD9834, which I believe is always on.
    The proof is in the pudding, however. I've yet to try it my way but I did buy a few FQPF7P06's just in case.:)