modern grid dip meter using dds

[neazoi]

Hi, is that possible to use a DDS oscillator to measure LC circuits resonance, similar to the old grid dip meter?
I guess there must be some kind of tuned LC that accepts RF from the DDS and be used also for the "grid dip function" for the external circuits to be measured?

 

[betwixt]

Conventional 'grid dip' meters (the name dates them!) worked by noting the perturbation in anode current as some oscillation energy coupled to a resonant load. In a DDS the 'oscillator' is digital and it's output is buffered so very little change in current would occur. However, if you added a resistance between a sense coil and DDS output then measured the voltage across the coil it should still work.

Brian.

 

[mtwieg]

If you use a buffer stage between the coil and the DDS output, then I suppose in theory the supply current into the buffer stage will change depending on the coil coupling to an on-resonant circuit. The sensitivity of this approach would depend greatly on the design of that buffer, in a similar way to the oscillator in a true grid dip oscillator.

I see a grid dip meter as a very crude and simple implementation of a single port scalar network analyzer. There are ways to do such a measurement besides measuring variations in supply current. Such as measuring the AC current in the coil like betwixt mentions above. Could use a RF power detector chip to get a very wide dynamic range.