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Sunday, August 26, 2018

More Homebrew Wisdom from Frank Harris, K0IYE


In Chapter 13A, Frank Harris writes: 

The Vanishing Art 

The 1986 ARRL Amateur Radio Handbook reported that hardly anyone was building homebrew ham receivers....  Out of hundreds of contacts, so far I’ve worked four guys, George, K7DU, Mike, NØMF, Biz, WDØHCO and Jack, W7QQQ who were using homebrew receivers for the QSO. Three of these receivers were made from vacuum tubes. George's receiver is a beautifully crafted instrument that looks like a commercial design from 50 years ago. All of these receivers had no trouble hearing me on 40 meter CW. I talked to one other fellow, Gil, N1FED who told me he had just finished a vacuum tube receiver. Unfortunately, it was performing so poorly he was still using his modern transceiver on the air. Gil told me he didn’t like transistors. I guess he found printed circuit boards and those pesky oscillations too much trouble. In spite of this pessimism, you CAN build transistorized receivers that work reasonably well. I built mine because I was intrigued by mysterious circuits like “balanced mixers,” “product detectors,” “cascode amplifiers” and “crystal ladder filters.” Before this project, I could recite the purposes of these circuits, but I had no “feel” for how they worked and why receivers are designed the way they are. What better way to learn than to build one? 

Aside from the need to shield circuit blocks from one another, a homebrew receiver with a single big board full of discrete components has another problem. If you build the whole thing at once without buying a kit and pre-cut board, I guarantee it won’t work. To make homebrew stuff that works, you have to develop your own technology based on parts you can get and circuits you understand. Learning to think this way was difficult for me. Rather than “building a receiver,” I had to lower my sights and build one circuit at a time, e.g., “an oscillator,” “a mixer,” “an audio amplifier,” etc. Then I put the blocks together to complete my project. Some of these circuit blocks didn’t work the first time so I had to build a new block. There were various reasons the modules didn’t work. Usually, I wasn’t able to buy the exact parts used in the circuits I was copying. Or my craftsmanship or shielding wasn’t adequate. Sometimes I never did learn why one version of a circuit block was superior to another. By building my receiver using separate little shielded modules for each circuit block, I could replace a circuit block whenever I managed to build an improved version. Otherwise, I would have ruined the entire big board.

On rare occasions my circuits didn’t work because there were errors in circuit diagrams in QST magazine or in the handbooks. I found some serious errors in my 1979 ARRL Handbook and a minor one in my 1998 edition. Perfect editing is not possible, so we shouldn’t expect it.

GET THE WHOLE BOOK HERE (FREE!) 
http://www.qsl.net/k0iye/

1 comment:

  1. I'm reading Frank's book as well - good stuff!

    You've mentioned this before on the Podcast, but it merits repeating: Don't underestimate the value of taking baby steps; there IS a learning curve - if it were easy, there'd be a lot less Icoms, Kenwoods and Yaesus on the air.

    That said, a basic DC receiver is a great place to start because it allows you to get familiar with the essential building blocks without going into information overload.

    Along those same lines, don't get hung up on trying to wring maximum performance out of your early efforts - learn to walk before you run. There's immense satisfaction that comes from hearing signals on a rig you built yourself - even if the rig isn't very good. That's something the appliance guys will never get to experience!

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