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Monday, July 15, 2019

The "Fish Soup 10" Homebrew QRP CW Transceiver

The box with the two grey knobs on the left is the Herring Aid 5, the receiver that took me 38 years to complete. The box on the right is a VFO I originally built for my first BITX40Module -- it started out around 4 Mhz but I pulled turns off the coil until it was in the 40M CW band.  The Altoids in near center has the buffers -- a 40673 MOSFET and a 2n3904 BJT. The box in the back holds the Tuna Tin 2.  There the oscillator has been reconfigured as an amp.  A relay switches the output from the buffers between the receiver and the transmitter.  That big switch in the center switches the antenna and the 12 V for T/R.  The circular black thing is piezo buzzer used for CW sidetone -- I have it glued to the board upside down to keep the volume down. 

The whole thing is mounted on a kitchen cutting board.  A breadboard! 

The most difficult part of all this was getting the needed 800 Hz drop in TX freq on transmit.  You need to do this with a rig like this or else you won't be in the other fellow's passband.  I did a lot of cut and try -- in the end I put a 5 pf cap across the coupling cap from VFO to buffer.  This 5 pf cap switches in on transmit via a small relay.   It works.  I just spoke to N8AFT out in Columbus, Ohio and I was in his passband.  

So five transistors in the receiver, two in the transmitter and three in the VFO/Buffer. So it is the  Fish Soup 10.  

It puts out about half a watt.  On CW.   I am feeling virtuous and vaguely superior. I've made several more contacts.  It all works very well and is a lot of fun. 


  1. I would love to hear more about the need for the frequency shift on transmit - never encountered that before.

  2. Royski: Peter VK3YE explains it very well here:
    73 Bill N2CQR

    1. Thanks Bill, that was a great explanation

  3. Your 40673 based SDR front-end popped up in Mike's video from yesterday: https://www.youtube.com/watch?v=ZWEgjIG2yf4

  4. Bill I have been noodling how to do that with my NE602 DC RX, I need to cut the tuning down, still tunes too fast, and need to put in offset circuit. Oscillator drift? Can't find it!!
    Ed KC8SBV

  5. Bill,

    Great sense of humor...

    I'm still under one watt. On CW. I am feeling virtuous and vaguely superior.

  6. Love it! Operating rigs of that sort is as close as we get to having a direct physical connection to the magnetosphere. Ride that ether, my friend. Ride it like you stole it!

  7. Nice working you yesterday. Super impressed with this setup.



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