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the "perfect" varactor

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mstechca

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No, I'm not showing you one.

I mentioned in Walter's 3-page thread about capacitors that I discovered that there is a band-pass and a band-reject filter.

If I'm not mistaken, a band-reject filter connected in a certain way will be a band-pass filter. The same is true for a band-reject filter. right?

So anyways, what I intend to do is convert these "filters" into tank circuits and control them both at the same time, so that hopefully two band-pass filters will see the frequency, and my equation stress will stop.

my varactor is the design Audioguru showed me, a diode and a capacitor in series. The center point is the voltage control point. I will be using two varactors now.

Because I want both varactor values to be the same at all times, do I need to use two DAC's to digitally control each one independantly, or can I use one DAC, and deliever the output to both at the same time?

I would rather use one, but I'm not sure what effect it will have on the entire circuit if any.

My DAC is an R-2R ladder connected to a 4024 counter.

Also, Does anyone know where I can find a list of diodes or transistors that work as perfect varactors? I want to obtain a wide range. I use 0.1uH inductors in my circuit.

So far, the best transistors that work as a varactor are the 2N2222, and the 2N3904.

Actually, if there is a large database that tells me the junction capacitance of many BJT transistors without having to download hundreds of datasheets, I would like you to tell me where to find the database.

thanks.
 
What is your definition of a "perfect varactor"? I'm asking because I would think it depends on the user and the application.
How are you going to use the two bandpass filters?
 
Ron H said:
What is your definition of a "perfect varactor"? I'm asking because I would think it depends on the user and the application.
How are you going to use the two bandpass filters?

He's talking about trying to tune his 'super regen', or at least a circuit that started off as a super regen :lol:
 
Nigel Goodwin said:
Ron H said:
What is your definition of a "perfect varactor"? I'm asking because I would think it depends on the user and the application.
How are you going to use the two bandpass filters?

He's talking about trying to tune his 'super regen', or at least a circuit that started off as a super regen :lol:
Well, I kinda figured that, but why does he need two BPFs for it? I guess I haven't been paying attention. :D
 
Ron H said:
Well, I kinda figured that, but why does he need two BPFs for it? I guess I haven't been paying attention. :D

He makes it up as he goes along 8)

He appears to have changed his mind about how it works? (or at least how it's supposed to work!) - I'm looking forward to the next crazy circuit :lol:

He could have hand wound IF transformers by now and built a proper radio!.
 
Nigel Goodwin said:
Ron H said:
Well, I kinda figured that, but why does he need two BPFs for it? I guess I haven't been paying attention. :D

He makes it up as he goes along 8)

He appears to have changed his mind about how it works? (or at least how it's supposed to work!) - I'm looking forward to the next crazy circuit :lol:

He could have hand wound IF transformers by now and built a proper radio!.
I guess we all have to follow our own paths to knowledge. :)
He doesn't irritate me near as much as he used to.
Mstecha, keep in mind that I'm a cranky old fart. I guess that would be pretty hard to forget. :roll:
 
I think he is tuning its "quench-oscillator" parts that are supposed to operate at an ultra-sonic frequency, way up at the RF frequency. It will be a super-oscillator! :lol:

Dual varactor diodes that are matched very well are available. But the Q of his tuned circuits is so low that they would have a wide bandwidth, so any diodes of the same part number would do. They could be fed from the same DAC with isolation resistors.
 
Nigel Goodwin said:
He makes it up as he goes along 8)
Welcome to creativity 8)
If a crazy configuration (according to all of you) works, why not use and expand on it?

He appears to have changed his mind about how it works?
No, I'm using everyday formulas to simplify the work.

I'm looking forward to the next crazy circuit :lol:
You are looking forward to it? LMAO! Are you willing to offer some cash? :wink: :wink:

He could have hand wound IF transformers by now and built a proper radio!.

hand-wound? omg. It will take me time to wind transformers by hand!

I think he is tuning its "quench-oscillator" parts that are supposed to operate at an ultra-sonic frequency, way up at the RF frequency. It will be a super-oscillator!
my quench section is already done.

Dual varactor diodes that are matched very well are available. But the Q of his tuned circuits is so low that they would have a wide bandwidth, so any diodes of the same part number would do. They could be fed from the same DAC with isolation resistors.
Then I'll use resistors. Thanks.
 
Do you believe in optimization? :lol:
 
mstechca said:
Do you believe in optimization? :lol:
Do you believe in evolution (as opposed to intelligent design)? :lol:
Your optimization process seems to be similar. If a random mutation is beneficial, it survives to the next generation. :D

Mstecha, we tease you a lot, but you're a good sport - either that, or you are very thick-skinned. :?
I have been one of your biggest detractors, but I admire the fact that you are very persistent.
 
Thank you.

I knew all of ya would (almost) give up on my superregen, but I wont. In fact, I'm testing my idea on my PCB right now!
 
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