Another really informative video Mike, thank-you. I'm very much a learner and had heard of varactors but now I know something about them. By following your videos, I'm beginning to understand how different parts combine to make the whole unit work.
@barryanderson5116
2 жыл бұрын
Boy !! I don't know. I learned a bunch with the solid state stuff !!
@dayleedwards3521
2 жыл бұрын
Hello Mike. You have spent HOURS on this, you are a VERY patient man.......I found this very interesting and thank you for taking the time.
@MIKROWAVE1
2 жыл бұрын
Ya - that is why I like the simple projects better.
@kensmith5694
2 жыл бұрын
The collector junction of a 2N2222 is good enough varactor for some purposes. To be extra clever with it, you can use the "Miller multiplier effect" to make it seem to have a bigger range. A resistor from the collector to a 24V (or so ) supply will back bias the junction making its capacitance low. If you bias the 2N2222 on a little, the collector voltage decreases so there is less back bias and hence the junction shows more capacitance. The 2N2222 starts to also make some RF gain. This means it amplifies the RF current coming through the collector-base junction. This is the "Miller effect" that makes the capacitance appear bigger. Basically you end up with a circuit that looks like a common emitter amplifier with adjustable bias and no input signal.
@MIKROWAVE1
2 жыл бұрын
Deep knowledge Ken! You are tempting these devices to do things that their mothers would not approve of!
@SeAfasia
2 жыл бұрын
Ok...nice presentation Mike....very helpful.. really...don't know much about theory components but your explanation are really worth....tks
@MIKROWAVE1
2 жыл бұрын
It is amazing how fast radio components were developed, perfected and mass produced worldwide in the early 20th century.
@SeAfasia
2 жыл бұрын
Yes...true....takes some germanium diodes from Japanese radio and working well...Many models at Greece also old radio with tubes... treasure
@southernexposure123
Жыл бұрын
I've been looking for and am very happy to find the information you're sharing. Thank you.
@benthere8051
2 жыл бұрын
The BB910 is a very linear device. Someone did a very good job on its design. Identifying the TL431's low noise characteristic was essential to this design. Good job, Mike.
@MIKROWAVE1
2 жыл бұрын
Those varactors make good FM modulators!
@jimmy_jamesjams_a_lot4171
2 жыл бұрын
I LOVE how you drew those LEDs in schematic!! It makes them look a lot more exotic or sophisticated than the regular diodes! What?! A community that appreciates the avant-garde components from surplus?!?! I guess it’s yet another example of everyone’s eclectic-esoteric-monasticism in EE?!! Oooohhh I love those old dual output HP function generators, with the crazy huge knobs that spins around once for every ten or so turns on it’s fine adjustment knob! Mine says ‘property of NASA’ on it, got it in San Diego so I suspect it was prolly at Raytheon or maybe Camp Pendleton. This video is serving me as a HUGE supplemental for learning about BIAS! REALLY COOL!!
@MIKROWAVE1
2 жыл бұрын
Wow! Sounds like you know where Murphy's Surplus is. No relation but maybe Murphys are surplus nut brothers. Glad you are viewing some of my vids.
@Steve-GM0HUU
2 жыл бұрын
Very interesting Mike, thank you. Useful to know that the varactor can be used to make a stable VFO given cost and scarcity of variable capacitors these days.
@MIKROWAVE1
2 жыл бұрын
I was surprised as well because I have never taken the time to do a real comparison before.
@wklinger79
2 жыл бұрын
I had an uncle that worked at Motorola in the television division many decades ago and he was on the team that invented the varactor UHF tuner used in television sets. My grandmother had a prototype television in her living room that was given to her by her son-in-law that was used in that project.
@nigelbrockwell6237
2 жыл бұрын
Very interesting and I've learnt quite a bit from your video, many thanks. Early last year I made a 40m / 80m Direct Conversion Receiver using the famous NE602. The main tuning was done using a variable 210pf capacitor and with an additional TV varactor diode for fine tuning. I did get a slight drift of frequency over about a minute and a half, but wasn't bad enough to become annoying.
@MIKROWAVE1
2 жыл бұрын
Where it gets annoying is when you are taking a portable outside and its hot or cold. Most everything stabilizes at room temp. But not all!
@nigelbrockwell6237
2 жыл бұрын
@@MIKROWAVE1 you're right. Luckily it is used at home in a set temperature.
@MirlitronOne
2 жыл бұрын
Thanks again Mike, 100% relevant to a current project I'm working on!
@MIKROWAVE1
2 жыл бұрын
Well that's great!
@XPFTP
2 жыл бұрын
i think it was a tentec 1250 regen kit. uses the varactor. cool lil radio. just the band selector was rough to use on it.. fun radio tho.
@MIKROWAVE1
2 жыл бұрын
Seems like every kit designed has a weak point!
@palipixel
2 жыл бұрын
Thanks Mike! Your VFO series has helped settle a lot of bar room bets & arguments about the details involved in modern VFO design. One caveat though (video production related): That heat gun has got to be the noisiest one on the planet. It must be right on top of your lavalier microphone when you use it. The YL here made some remarks about it as well. Fix it in post? Otherwise, jolly good show and carry on! 73s from '6' land.
@MIKROWAVE1
2 жыл бұрын
You make your XYL watch my videos. Oh the humanity! I'm done with the gun!
@MrtechElectronics
2 жыл бұрын
Use zener diodes for larger capacitance. I'm using 12v zener diode (40pf) for FM radio tuning
@MIKROWAVE1
2 жыл бұрын
Very cool.
@Dazzwidd
7 ай бұрын
That's interesting
@PapasDino
2 жыл бұрын
TNX Mike, great series! 73 - Dino KLØS
@MIKROWAVE1
2 жыл бұрын
Thanks for watching Dino. Wish I had room for a chamber!
@eduardmichalek5445
2 жыл бұрын
I am try old zener diode 8NZ70 (17V). This ZD tune more then 500 pF with 12V.I'm tested in vfo 2.5 MHz and cca 3 uH. But be carefully. One electrode go out thru glass and p/n is sensitivity on light, whitch change capacity. It is similar like photo transistor 😊.
@MIKROWAVE1
2 жыл бұрын
Wow that is a great experiment.
@Dazzwidd
7 ай бұрын
I still call it a varicap, I go between calling it varicap and varactor depending upon the subject. I have seen LEDs used as a varicap, but personally I use low power silicon rectifier diodes if I'm being stingy. At HF you can get away with a bit! LEDs make great zener diodes as well
@R2AUK
2 жыл бұрын
🔥👍
@MIKROWAVE1
2 жыл бұрын
Thanks Alex.
@ktheis1
2 жыл бұрын
Wondering if a varactor could be used as the regen control in a regenerative receiver in place of a ceramic capacitor?
@MIKROWAVE1
2 жыл бұрын
I would not be surprised if this has not been done already!
@peterfitzpatrick7032
2 жыл бұрын
I have some heavy duty rectifier diodes (M8 stud-mounted) I pulled from a 3 phase MIG welder... I might use them as supercaps!! 🙄😅 BTW... Is the toroid using a powdered iron core or ferrite ? 🤔 When you swapped the pot leads, did the log output not flip ? (antilog ?) I'm liking this vid format, you sir, know your stuff... From the Emerald Isle 😎👍☘🍺
@MIKROWAVE1
2 жыл бұрын
How Studly! I flipped the pot leads so the dial went 0-100 going higher in f before I added the curve compensation resistor. Low Ai Powdered Iron works OK. Ferrite drifts nasty fast. I tried 61 and 43 ferrite and no go.
@DAVIDGREGORYKERR
2 жыл бұрын
can we use a MC14551 plus a 10.240MHZ crystal plus the channel switch out of a CB transceiver to control a MC14551 to stabilize a VFO?
@MIKROWAVE1
2 жыл бұрын
I don't see why not. Those old Mot PLL chips were very flexible.
@oilydigits
2 жыл бұрын
Mike, another very interesting video. VFO design and construction could be a hobby within a hobby. 73 Steve M0KOV
@MIKROWAVE1
2 жыл бұрын
Drifting off frequency has been a hobby for me. ha.
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