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Thursday, August 4, 2022

Farhan Takes us Back into the Daylight -- An Analog Rig with a Homebrew Crystal Filter and an LC VFO


There is so much radio goodness in this rig and in the blog post that describes it.  Farhan's blog post will keep us busy for a long time.  There is much to learn there.  But perhaps even more important is his larger view of the role of analog circuitry in ham radio.  Here are a couple of excerpts from his introduction: 

 Here is the memo : The analog never died. The world is analog all the way, until you descend into Quantum madness. The antennas are analog, Maxwell died a content, analog man. Our radios, ultimately, are analog machines and we are all analog beasts too. Amateur Radio technology has evolved into the digital domain. However,  it has only made it easier for us to do analog with computers to simulate and print our circuits.  So, it’s time to bid good bye to our Arduinos and Raspberry Pis and build an Analog Radio for ourselves. So let’s see what we can achieve in hindsight, a return to our native land and a rethink of our approaches. The radio is called Daylight Again, a nod to being back at the FDIM in 2022 after a gap of two years. It is named after the Crosby, Stills, Nash and Young’s song that had been humming all the time while put this radio together, emerging after 2 years of lockdown.  This radio that took two days to come together, no actually two years! That’s: parts of it got built and stowed away, thoughts were struck in the shower, questions popped up during early morning cycle rides and notes and circuits were scribbled in the notebook.  I must take the first of many diversion here: I hope you all maintain a notebook. Write down the date and whatever you thought or did on the bench and the result. Nothing is trivial enough to leave out. Wisdom comes to those who write notes.  I started to build this on Saturday the 14th May and I checked into the local SSB net on Monday morning, the 16th May 2022.


Having clean VFO  is the most important way of increasing the dynamic range of your radio. A free running JEFT VFO that has sufficient power and a good Q components, will be unmatched by any synthesized or direct sampling radios. The math is all on the side of the free running VFO. We are talking -150 db/Hz at 10 KHz spacing, by comparison the Si5351 is -125 db/Hz, it is 300 times worse.

That is just part of the intro.  We should all study the rest of Farhan's blog post very carefully and incorporate the wisdom into our new rigs: 

Here is the blog site: 

Enough of the darkness.  Step into the daylight my friends. 


  1. I have been studying this latest creation
    from Farhan since I saw it in the latest QRP Quarterly magazine about a week ago. 
    I am especially interested in the transmitter section since in all my years of homebrewing I have never been able to produce a satisfactory and substantial Phone signal of at least 10 watts, either DSB or SSB, out of the NE602. 
    To me, the phone QRP definition of ten watts is the least amount of power needed to have a little fun on 40M and therefore make the rig worth building, and 25 watts is ideal for having lots of fun, which is always a goal of mine.
    My current project over the past few months has been a 40M version of the Perigrino using the NE602, and I have tried several completely different transmitter RF amplifier strings, but every time I get above a few watts output I encounter what I am guessing is distortion-induced (possibly due to unbalanced carrier, and I have never had any luck with my NE602 carrier-balancing experiments) power mosfet self-oscillation, which occurs immediately after switching to transmit.
    Therefore, I will now be trying to get to the 5 watt level at least with Farhan's design, and then I will add a final power mosfet stage from there at 24 VDC, but if anyone has what they think is a very stable design for 25W out of the NE602, please contact me.
    Best Regards,
    Orlando, FL

  2. Another brilliant diamond in the rough. Ashar is a master designer but more than that, like a Renaissance master, he is able to conceptualise a design but leave it a scaffold for less experienced artists to fill in.
    I'm intrigued by the reversion to what are effectively dual gate MOSFET mixers, a high gain audio strip, no Receiver IF gain, and a simple free running JFET VFO.
    I also note the clever use of parallel 2n2222 to drive the IRF510 gate, avoiding the unobtainable 2n5179s etc.
    Time to fill in the schematic errors and melt some solder to hear this one for yourself.
    73 Paul VK3HN.


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