Experimental Transmitter

 
 

A good way to learn how to build something complicated is to break it down into blocks that you understand, build those one at a time, and then link it all together. That’s my approach here. I had no expectation of building a highly-polished transmitter; I just wanted something that would provide CW/SSB capability and modest power (~50 W) on the HF bands. Most of all, I wanted to try my hand at basic RF design and have a good time! This project took about seven months.

 

    Transmitter Pages





Keyed Waveform Shaper


Two-Watt Driver Amp


MOSFET Power Amp


Lowpass Filters


T/R Switch


T/R Sequencer





PERFORMANCE



Coverage: 3.5 to 30 MHz


> 35 Watts output, all bands


All harmonics  < -60 dBc


T/R delay: 11 ms


Optimized keying bandwidth,

4.2 ms risetime

 

Building Blocks for Flexibility... and Learning

The enclosure you see above was originally an audio power amp that I built in my high school days. For the transmitter, I recycled the power transformer and huge filter caps, along with some of the mechanical stuff. The power supply provides 1.2 - 30 VDC at 4 A continuous (6 A max) with excellent regulation. It’s based on an LM317 with a moosey pass transistor, also lifted from the audio amp.  This is a general-purpose power supply (see the binding posts on the panel), but with plenty of room for the transmitter modules. So if I decide to trash the transmitter later, this box will live on as a bench supply.


There’s another little transformer in there to provide other bias voltages: ±12 and ±5 at up to about 30 W, total.

Recycled Power Supply and Chassis

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