RF tutorials - The Varicap or Varactor Diode

[@VikasVJois]

Good explanation with practical example applications

[@visai3634]

well explained. Now i understand why a varactor diode used in microwave receiver used in lab equipment. You are an excellent teacher than my professors.

[@FantaBH]

Even I do know about this from before I think 35 years, it is good to hear it again on such nice and well-explained method. Thumbs up and yea I did subscribe to your channel a long time ago. But the first time I comment.

[@acestudioscouk-Ace-G0ACE]

This is a really useful video, I've just watched it again as I'm building a crystal set and using a varicap instead of a variable capacitor.

[@omeridan8815]

I like your videos, keep it up

[@valeriucasapu1558]

Thank you for the clear explanation.

[@Plons0Nard]

Leds can also be used as varicap. Great channel. 👍🏻🤝🏻🇳🇱

[@greglivas701]

69pF. Nice.

[@Scrogan]

Neat, I never knew these were used at high power to generate higher harmonics! I wonder how optimised that kind of circuit can be? Also I’ve heard that common LEDs make decent varactors, though I’d have to worry about photocurrent, particularly under AC lighting.

[@arciecuevas5017]

Can you do a video on parametric oscillators and parametric amplifiers with controlled variable reactances?Thanks

[@thezodiace7399]

Excellent video FesZ, can you do a series on RF electronics starting from the basics for non-RF engineers?

[@FesZElectronics]

I do plan on making more RF related videos. Thank you for the suggestion.

[@philippeversailles2170]

Thanks for this video. I have discovered there are varicaps in LTSPICE native models. Adding previous video on mixers with this one (VCO) plus notions of SSB you also developed previously ..It seems we are on the path of Ham Radio, no ? By the way this is great!

[@FesZElectronics]

Well I do try to keep things a bit more diverse, and one of the things the viewers and my Patrons requested was RF radio related stuff. Happy you are enjoying it! Cheers!

[@MrAmalthejus]

@@FesZElectronics Sir, so if I connect a DC voltage source, a Varactor diode and an inductor all in parallel, there will be oscillations? Did I understand it right?

[@dimitrioskalfakis]

good edutainment!

[@stefano.a]

The electrical charge in a diode is *inside* of the depletion layer and not in the remaining parts of p and n zones. p and n zones are electrically neutral; they became partially electrically charged near the junction (the n zone near the junction became positive and the p zone became negative)

[@audiokees4045]

When I use no ferrite bead before the varicap the vackar oscillator stops, or better does not start. Some ferrite beads also do not work.

[@Arijit_VU3ICT]

Thanks a lot sir... Please make a video of vfo and bfo and their usage..

[@IBasilisvirus]

what is a "dc bias"? he mentions it when he applies dc to his circuit

[@FesZElectronics]

Well, by definition, "to bias" a circuit means to apply a voltage to set a specific initial operating condition. In this case, what I was trying to say is that by applying this external bias, I am setting the initial capacity of the diode (the capacity is voltage dependent).

[@adrienferreira4666]

Hi FesZ, I'm a big fan of your channel! At 9:11, what do you mean by "they're both referenced to ground without being directly polarised"? Is there a terme I can Google to learn more about this concept?

[@FesZElectronics]

Maybe I didn't use the best choice of words.. I was trying to say that even though the 2 diodes seem to be oriented in different ways, the DC voltage is reverse polarizing both the diodes. D4 has its anode directly to GND, but D2 also has its anode connected to GND trough L2.

[@adrienferreira4666]

@@FesZElectronics ah, I get it! Thanks for having taken the time to answer my question. Keep on the good work :)

[@avonfonds2567]

Hello thanks for the nice explanation, can I use this to tune FM transmitters frequency by replacing the old conventional variable capacitor I want to make it tunable with my microcontroller by applying a reverse bias protentional as you said (my idea is to use a external dac)?

[@FesZElectronics]

That should work. In general this is how radio receivers are built nowadays - you no longer use mechanical variable capacitors but rather varicap diodes and a bias voltage. For the transmitter, as long as you are working on the low power oscillator, rather than the output power amplifier, there should be no issue.

[@avonfonds2567]

@@FesZElectronics oh thanks for the reply is Variac diodes dead now or still available ?

[@thezodiace7399]

won't the C2 get on the total measured capacitance of the LC circuit as well?

[@FesZElectronics]

Are you referring to the circuit at 7:18 ? There C2 is in series with the varicaps, so the total capacitance is the equivalent series capacity. But considering C2 is in the order of 100nF and the varicaps are ~100pF then C2 can be neglected.

[@thezodiace7399]

@@FesZElectronics Yes Thank you for your reply.

[@janpolanton5574]

Hello: i wonder if there is any way to put a comment on error or limit in a behavorial source (exemple : B1 n001 n002 V=if(V(V+) >3 & V(V+)

[@FesZElectronics]

Hello Anton! I don't think there is a way to create a pop-up or other text based error, maybe just measurement statements that can be read trough the error log. Personally I guess I would do this by creating the behavioral source with a Boolean output, like V=if(condition, 0, 1) and just check the plot at the end to see if it ever goes to 1; this way you can also see when exactly the error condition occurs.

[@janpolanton5574]

@@FesZElectronics Thank's for your answer. I wil try with a boolean output. I've made an LM39xx model based on the datasheet but I have not yet implemented the voltage supply limit. I was hopping for this comment solution. If you have any interest for this model, just aks me.

[@FesZElectronics]

Hello Anton. Unfortunately most models do not implement a feature to indicate if the circuit is operated poorly, or would just brake. LTspice will not care if you run 1KAmp trough a 1N4148. So its quite nice that the model you are making will have some way to indicate a fault condition. Honestly I would not go for the comment solution, because for example if you are simulating a circuit that starts with supply from 0V (to simulate start-up), then, right at the beginning your circuit would indicate the fault and stop simulating. I would however use the improper operating condition to affect the circuits behavior. Say if the supply is not in 3-20V, then the input after a BV source is 0, regardless of what is on the input pin of the model. So to add this filter condition right at the beginning. This way, if the operating conditions become ok later, the circuit starts working.

[@jonnupe1645]

How can I use these components to reach low frequency, within the range of 1-50hz?

[@unknownpresident]

Hello ......

[@FesZElectronics]

Hello!