Off Topic: is there such a thing as an integrated circut chip as variable inductor?

[john doe]

Posted on December 12, 2017 at 05:06

I'm trying to learn antenna matching and I'm as much a 'do the math' guy as I am 'hack it out through trial and error' kind of person.  Usually it's both, when I'm not getting it.  And I'm not getting tank circuits right and I dont have a large set of inductors to play with.  Is there a chip that is a variable inductor with a digital interface?  I should have just built the oatmeal container radio and moved on to motor controls.

:)

[Oliver Sedlacek]

Posted on December 14, 2017 at 11:15

RF circuits are usually electronically tuned with varactors, capacitors that vary in value with DC bias. You could achieve a similar effect with saturable inductors where you use a DC bias winding to adjust the core permeativity using the non-linear behaviour near saturation. Having said that, I doubt it's easy at RF frequencies.

I also think you really are going to be better off with a pre-approved module (including antenna) as the cost of certifying your own module will probably be $50,000 to $100,000.

[waclawek.jan]

Posted on December 14, 2017 at 11:42

using the non-linear behaviour near saturation. Having said that, I doubt it's easy at RF frequencies.

Huh, easy or not, I wouldn't want to do that in RF, generating a slew of harmonics. which in turn need then to be suppressed somehow....

JW

[Oliver Sedlacek]

Posted on December 15, 2017 at 10:31

I offer it more out of academic interest than as a practical suggestion

[AvaTar]

Posted on December 15, 2017 at 11:01

Varactors would be less academical, with tuning achieved by driving the bias voltage with the DAC.

Just some level-shifting circuitry is required.

However, I do not see a convincing reason for a standard MCU in this context - the IF frequencies are a bit over the head to process, and the audio can be done much cheaper.