60 Meter SSB Transmitter

A QRP SSB transmitter presented at OzarkCon 2006

 

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This page describes a 10 watt (or so) transmitter I designed for the "new" 60 meter band.  I wasn't particularly interested in becoming a convert to SSB, but I did want the experience of building an SSB rig.  At a time when the project was languishing, the leadership crew of the OzarkCon QRP convention in Joplin asked me to do a presentation.  So I decided to get in gear and finish the thing off.  It almost worked the other way around, but I did get it working in time and was pleased with the results.

Click for my PowerPoint slide presentation (2MB).

The PowerPoint slides contain all the schematics and minimal descriptive text, but it's a big file.  Below I'll show the schematics and provide some descriptive as well as a link to a more complete text file.

 

(Click schematics to see a larger version)

 

Block diagram:

The design is a conventional double balanced mixer and crystal filter, mixed with a VFO (DDS) to the output frequency and followed with several stages of amplification.  Only took a sentence to say it, but over two years to finish the project!

Audio stages:

I use a preamplifier with limiting followed by an active LPF/HPF filter combination for bandpass filtering of the audio.

Start with the speech (microphone) amplifier using the LM387:

 

After the microphone amplifier is this bandpass filter, consisting of a lowpass and highpass filter in series.

Next is the 9MHz carrier oscillator:

 

Then the audio and 9MHz L.O. are both fed to the double balanced modulator (DBM):

After the DBM, the 9MHz double sideband signal has one sideband trimmed off by the crystal filter:

Next we need a VFO to mix with 9MHz and produce the 5.3MHz output.  I used the NJQRP AD9850 DDS board and programmed a PIC to control it:

 

The 9MHz SSB signal and 14MHz VFO signal are mixed in an NE602 mixer chip.  It includes an output filter to remove the image frequency:

Now I have a very small 60 meter SSB signal.  I'll need two stages of class A small signal amplification followed by two stages of power amplification to get to 10 watts.  First stage class A:

A very similar second class-A amplifier takes the power level to 100mW:

The final stages are push-pull power amplifiers.  The first gets to the 1 watt level:

The final amplifier is shown in two drawings.  The first is the basic amplifier and the last shows the biasing circuit for the amplifier, plus the output lowpass filter.

And here's the bias control circuit and output harmonic filter (below):

The project never quite made it into a box.  At least not yet.  Here it is in 10 or so separate boxes, with one or two boards not even in a box:

Click below for a Microsoft Word text file with considerably more detail on the project.

Design Notes for the 60 meter SSB TX

Finally, here's a Word file of my rough notes made during design and testing:

Diary of a QRP homebrew madman

73,

Nick, WA5BDU