hmm.. what you describe seems very different than my understanding. a varactor is a variable transformer. the big nob on a varactor simply sets the turns ratio. i've used a varactor a couple of times like this.
Varactor diodes also know as varicaps .Are used a lot in programable frequency oscillators also know as VCOs and others more sofisticated with PLLs . A simple circuit oscilator with transistor and some kind on programable of voltage source .And you have a programmable oscilator .Is elegant and straight forward way to interface digital electronics with comunications cicuitry .ALso modulation schemes are also posible like FM and digital very simply !
Varactor diode or varicap is voltage dependent capacitor. It can be used in oscillators for frequency change purpouse, in phase shifters to change phase of signal with voltage etc. https://en.wikipedia.org/wiki/Varactor
hmm.. what you describe seems very different than my understanding. a varactor is a variable transformer. the big nob on a varactor simply sets the turns ratio. i've used a varactor a couple of times like this.
Varactor diode offers DC isolation. Not larger capacitance, but variable capacitance (not fully linear). Not practically used in guard rings. In fact guard rings uses process technology, not by circuit and device technique today. Perhaps in the older days when process technology is not so advanced.
In classical VCOs, varactor diode is used for fine control the resonance frequency.
One of the peculiarities of one varactor is that if the voltage in his extrems increases then the resistance of the varactor below and viceversa.
The use of this characteristic allows to make constant the current that circulates in a resistance ready in parallel with varicarp. In the thelephone's systems is used to carry out the equalization of one phone with independence of the distance to the central (currrent of the micro is constant and you don't note diference in the sound's intensity bewteen a person that is far to you and other that is near)