On Mar 4, 2025, at 9:05 AM, atlasstuff via <g4fph@...> wrote:

For many years' now, I've had one of the early 'miniVNA' units from Mini Radio Solutions sat on the shelf. It doesn't get much use these days, as it's functionality is bettered in most respects by a nanoVNA from China that I also have.

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The oscillator in the miniVNA is a DDS-type, using the 14-bit, AD9951 IC by Analog Devices. Output from the 'DUT' (Device Under Test) BNC is a high-quality sinusoidal wave at exactly the right level to apply to the FT-301 external VFO input:-)

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I hacked together a quick programme for the PC (using the ancient BBC Basic for Windows language) to allow entry of data for band, stepping of the (RF) frequency and trimming of the DDS reference number. The programme does the necessary maths and formatting and sends the required data (simple ASCII text strings) to the miniVNA to get it to output frequencies in the 5 - 5.5 MHz range.

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While the stability of the internal VFO of the FT-301D I have on the bench is excellent, now I have a 'digital' alternative. Ironically, the reference crystal for the DDS in the miniVNA seems to drift a little until it's been powered up for an hour, or so. In fairness, this drift is not an issue when using it for what it was intended for.

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It would be a straightforward job to drive the miniVNA from an suitably programmed Arduino, with some buttons, display and shaft encoder and dispense with the PC altogether. One day, I just might...!

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Regards,

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Mark, G4FPH.

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