It is a complete, finished radio for $45!! Of course it is a compromise, and you have always been frank about the design issues.?
I am not complaining. I had fun putting this together, and I¡¯m learning more from this one project than several years of other experiences. Just understanding the costs and compromises of the design decisions, and their effect on the final performance, has been a great lesson, and it is ongoing.
I will continue to explore, first the limits of changes to the analog vfo onboard, and then possible learn to build an outboard vfo.
I also look forward to the opportunity presented by the DDS VFO and learning about the Arduino architecture.
I find it hard to imagine a better way to spend $45 or $59 for an education.
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I will be frank. This design is a compromise. The VFO should have been on a separate board. I thought about it for a pretty long time. There was no cost difference. There was just one more board to hookup and wire up. In the end and after countless conversations with some co-builders, I decided to include the VCO on-board. I am still convinced that this was a better option than an outboard VFO for easy of use.
Here are some notes from my experimentation.
1. It is NOT about the capacitors. I build a two-tone oscillators using these caps that run at 14.000 and 14.200 MHz directly. They are so solid, I can't believe that it is a free running oscillator.
2. The culprit is heat. The RF amplifiers have significant current, there are three of them. The heat dissipates through the ground plane and heats up the VFO components. This heat would be missing if we used through hole components as those components are off the board.
3. The heat sensitivity is also due to it being a VCO. The varactor tuning couldn't be avoided as getting good quality capacitors is very tough these days.
If you'd still like to retain the analog tuning, do what bill suggests. Build an outboard VFO, shield it well and it will be rock stable.
- f
