2017-12-11 08:06 PM
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.
:)
2017-12-13 03:58 AM
You may be thinking of a gyrator. Google 'gyrator circuit' ... but don't expect it to work at RF frequencies!
2017-12-13 04:32 AM
There are motorized tunable inductors around, but fine matching is usually achieved with electrically tunable capacitors.
You did not specify what frequency and power ranges are you talking about. For starter you might want to have a look at
http://www.st.com/en/emi-filtering-and-signal-conditioning/smart-antenna-tuning.html
JW
2017-12-13 04:36 AM
For antenna tuning, there is this component which is the tunable AC capacitor: (instead of inductor)
http://www.st.com/en/emi-filtering-and-signal-conditioning/rf-tunable-capacitors.html
2017-12-13 05:53 AM
I would have guessed the VHF range, of about 100MHz.
The simulation of adjustable inductances by opamp is not new, but mostly for the audio range.
Electronically tunable capacitors are usually implemented via varactor diode, with a (high) bias voltage commutes the capacity.
2017-12-13 07:10 AM
Electronically tunable capacitors are usually implemented via varactor diode, with a (high) bias voltage commutes the capacity.
Yes that's the usual way; but the STPTICs are different, based on ferroelectric effect. Another interesting option are
http://www.psemi.com/products/digitally-tunable-capacitors-dtc
capacitors, basically a bank of capacitors in series with switches, integrated with decoding logic.There are then also motorized capacitors, too; it's not that unusual to use motorized vacuum variable capacitors for certain high-powered applications.
JW
2017-12-13 07:28 AM
Motorized caps are probably a bit oversized for a radio applications ...
And yes, varactors are around for a few decades now.
These varactors, together with NVM, allowed for an electronic radio/TV station memory - no more turning complex and skidding cable-operated varicaps ...
2017-12-13 07:34 AM
What I know if a tank circuit needs an adjustment it is done with capacitors. Real high frequency ICs. have capacitance and inductance inside the chip or with the bond wires, I think there are no tuning in them.
2017-12-13 09:00 AM
Motorized caps are probably a bit oversized for a radio applications ...
Define radio... :)
2017-12-13 11:39 PM
Define radio... :)
The O.P. wrote: > I should have just built the oatmeal container radio ...
Thus I assumed it's not about a complete 100kW broadcasting station ...