Mike, I can only thank you for putting up such a lovely set of very informative videos about radio and using tubes and semiconductors. I hope you can do many more. Balanced modulators etc. and phase locked loops. One of the most down to earth real radio hams I have ever seen. Just wonderful and I am learning loads even though I already have a degree in electronics from Oxford. Please make more.
OK.. The use of a Varactor in place of an "Old School Plate Capacitor" gives me an Idea to use one to tune a Frame Loop Antenna.. Easy to feed a Variable voltage rather than trying to control a Servo Motor to move the "Physical" Capacitor Plates.. 👍👨🎓Thanks for Posting 73s
When I was a very young kid building my first crystal set I was so impressed it worked when I hooked the ground wire to a water pipe. Could not understand that the ground was a big part of it's operation. Thanks for your vids. Carl, AB1ZI
I ordered one of the NTE618 varactor diodes from Amazon immediately after watching your video. I received it today and incorporated it into the circuit using your ferrite rod receiver - "Spare The Rod? Spoil the Crystal Set". The varactor works very well with the ferrite rod. I am really impressed with the performance of the varactor diode. There's a big hole in the prototype where the 365 pF cap used to be. The NTE618 diode is tiny but its performance is huge. I have a lot of tests to perform. I'm going to see what range I'm getting. I have a signal generator I can use to test the range. Most of the stations come in in the upper portion of the band where the voltage on the varactor is at 1.5. volts or less. I'll do more tests and report more later.
This was both useful and interesting. I need to watch it again to take it all into my geriatric mind! I'm guessing purists would say you can't have batteries in a crystal set but it's certainly a good alternative to mechanical capacitors.
I have not tried Varactor tuning for the BCB but I do use it for tuning my 40M DC receiver with a pair of 1N914 switching diodes in parallel and it tunes 15 KHz ( 7.029 to 7.045 ) of the portion that I normally listen to. I loved the Book Condensers used in the 1920's Crosly radios in my collection years ago 🙂
I used to get police calls off our wall phone in Detroit on a cheap transistor radio. Picking up their "IF" at 1650 - 1750 MHz? I wonder what an audio taper pot. would do for the band spread here? I like that Varactor Tuner idea.
Excellent! Ive seen those linear shaped capacitors before and always wondered why they were shaped that way, stunningly obvious when you point it out. PS my background is not radio, its dc or digital stuff :)
Great video. I would have liked to see additional testing with MOSFETs and leds but what you did was awesome. Looking at the special variable cap you had made me think about making a cap using PC boards and shaping them in a similar way to linearize them.
Can you make a nice simple veriometer setup? Would love to see this in a crystal circuit of yours. Perhaps this will give you a wider range in your varactor radio too. Keep up the great work!
Thank you. You do things differently to all the other videos on varactors that I have seen so far. What I loved was that you put in different diodes and compared. That is brilliant teaching 👏 😀. I am getting a feel for the varactor now. Thank you so much. You are what makes the Internet a gift for everyone else. You also empower people like me. Thank you.
@@MIKROWAVE1 I am trying to build a monophonic synthesizer with the designs from other people but I want to understand what every component does. Eventually I want to design my own. Sometimes electronic components are used unconventionaly and can throw me. You did a stellar job in explaining this. Again thank you. You may not realise it but your teaching also gives me the confidence to try and try again. So ,just thought you should know that.
Very helpful thank you. I found this video just when I was wondering where I was going to find a decent source for tuning capacitors for my home projects.
Mike, thanks for another great video and for investigating a wide range of devices and configurations. As a regulator, for accuracy a Zener has to pass significant reverse current. It seems unsurprising that, when instead it's used as a varactor with a similar applied voltage, it loads the tuned circuit. TBH I wasn't expecting the Zener to work even as well as it did.
Hello! Good work! I made several experiments with a crystal radio and made some conclusions. The crystal radio has a good sensitivity when we have high quality factor of input LC resonance circuit. There can be a variable inductor (a ferite road is a good choice ) and there can`t be a variable capacitor - because it decreases quality factor. Next - you can`t shunt an input resonant circuit (a coil and an antenna): because quality also will be increased. As a very good solution - you can use a RF mosfet: for example BF998 (with connected gates 1 and 2 in parallel ) as a synchronous switch.Connect gate(s) to the hot wire of a coil (i.e. an antenna), source to 1/4 part of a coil, drain - to an RF blocking capacitor to a ground (common). You can use 250 Ohm small earphone but it can be connected through an electrolytic capacitor to drain. I had an excellent results - this crystal radio receives a noise of AC current from AC main in a village. I had an antenna - 15meters of wire with feeder that had been connected to middle of antenna . You can much improve selectivity wen you use an additional LC circuit with a 68pF capacitor .
This is a nice video, great comparison between the diode types. I just used a varactor diode in a receiving only antenna system to tune it across the bands, and it works really well, thanks for the confidence boost to get me motivated.
You almost don't need a switch on the bias supply for the varactor. The max leakage current is 100 nA and a 50K pot would give you 180 uA. You might even be able to generate your bias supply off the antenna with a voltage doubler detector. I am impressed as well. I think you just put the 365 pF variable capacitor guys out of business. I am really impressed.
You are truly blessed. You must live in an " RF " mute zone. Anything you build tunes in numerous stations, and they all sound as if FM quality. However, I would like to know what you are using for a long wire antenna, and its length. I ( on the other hand ) live in a Microwave. Extreme amount of noise on everything, even with top modern day receivers, extreme amounts of noise. I have built replicas of your crystal receivers, and have yet to receive anything but crackles, pops, and noise. I do like the varac diode receivers, and just for the fun, am going to build one. Who knows, maybe this one will work. Great work on you part, very knowledgeable. Keep up the great work. Jim
Varicaps are hard to find these days. As are tunnel diodes. Instead of varicaps I used LEDs. The older types, greenish yellow were the most suitable for this application. Enjoyed and enjoy 🤝🏻👍🏻🇳🇱
Workarounds and Tricks like this are great fun, but it depends on how much Q you need, and the application. I have been able to find all kinds of Varactors lately. Thanks for watching!
You can power the varactor diode by tuning in a local high power radio station and rectifying and filtering its output. A UA-cam contributor (W1VLF) generated 27 volts at considerable power using that technique.
I want to drive the varactor with a sawtooth waveform. I would then feed the recovered carrier to a scope as a sort of primitive spectrum analyzer. I could optimize the receiver for each station I wanted to receive. That would be great fun.
This is really a cool video. The Remco looked cool but the rocket radio was the best. It had a ferrite inside a much smaller coil. I once made a crystal FM receiver, no batteries, 1N82A, it only received 2 stations but it had a very short antenna. I could hold it up in the air and pick up the signal. There was a fair amount of distortion because it didn't have a true FM de modulator but it did work. To be a "real crystal set" you need to get rid of that battery. You could do it by having other diodes going to a large cap creating a power supply from the RF depending on the needs of the varactor. I saw one once where the RF power ran a transistor amplification stage, no batteries. It was in an old book "101 Electronic Projects". If I did a design today I would start by picking the strongest station and set up a crystal set as a power section tuned to that station, (might not need rectifying ) rectify the output then go to a buck boost section to get the voltage up. I would also try to design the varactors so that they used the lowest possible voltage. Do you remember the CK722? They had a can with a glass base, the can rusted. I believe it was the first transistor a mere mortal could buy. Wow, I checked ebay for varable caps and some were 70-80 bucks! I have a big box full of them out in the barn. Thanks a lot. Keep up the good work!
Taking those steel shot, you can slam them with a sledge to make 2 opposing flat spots to make drilling them by hand possible. Good variable tap for your tuner.
Howdy. Good information. I have been looking for some large value varactors for some time. I located 11 items of the NTE618 at TME and ordered them. Thanks for providing the type. I would like to point out that using two varactors in anti series will reduce the max. capacitance to half the value. One may want to replace the upper varactor with a fixed cap of say 10 times the varactor max value. I.e. 4n7 or 5n6 plastic cap, or for best quality, cercap. Large cercap.s are available. Practically all varactor bandwidth will be available. High regards.
Hello Michael, great stuff as usual...! So I would love to see a TRF preselector using "ganged" varactors. These dual gang TRF air variable capacitors are expensive and I expect many of us would benefit from doing the job with varactors... that would be a fantastic...! Thank You, Michael...!
Would have been nice to see the use of more modern varactors with greater linearity. Something like an NXP low voltage BB201 dual diode common cathode device that is much cheaper than the going obsolete NTE618. Great video. You've also explained why my IN1007 based regen radio sucked so much with very little tunability. I'll switch out the IN1007 for proper varactors. [edit] The BB201 on Mouser are 83 cents in one off quantities and 73 cents for 10 or more.
The BB201 is not optimized for a.m. radio. The capacitance range is too small. It might not be a bad idea to pick up a few NTE 618 just to have them on hand.
Great video, thank you for the clear explanation and for the practical tips too. Could this technique be used to remotely tune receive loop antennas ? Would it be posssible to have a variable bias T that could send a control voltage?
The variometer designs are neat. Awesome examples! Amazing, the capabilities for the 3D printers... especially for metamaterial like designs and not only the parts of a design. Electroplating the 3D printed parts seem like another way also for more exotic designs. I've been wondering about stealth antennas for fox hunting using the sewing machine to stitch... I suppose kind of World War era design like. Thanks for sharing. Reminds me I wanted to check and see what the Cricut Expression I own now can cut in regards to sheet aluminum, brass and/or copper.... looks like a no go unless a foil on another plate medium. HHhmmm... wondering what the COTS CNC lasers can do without O2 or how many parts can be cut from a sheet in the most cost effective way if outsourced to a fab shop project way? Anyways... the digital components are neat and super practical for more automatic processes. Thanks for all the details and specs. as well!
@@lysippus I was jotting down my thoughts while watching the video, that's all there comic relief bot. I do wonder with the mind control... what the handlers come up with based on memory associations for cues, keys and triggers. Guessing they are liable for many of the head traumas over the years.
Excellent, very good vid. It has got my interest in 'crystal radio' again. Curious if forward biasing the detector diode will help the reception. Thanks 73.
Mike, I have a question for you about your dual veractic crystal radio. I recently built one and I made a circuit board to mount the components onto and I worked from your schematic diagram and made sure that everything is in order , but I have not been successful on getting it to work at all. So I am using a 10k potentiometer and in your opinion do you think maybe the potentiometer value is not high enough for it to function ? It doesn’t seem like it’s receiving anything. I’m going to try a 50 K potentiometer next. The next question I have do the primary and secondary grounds go together from each coil ? According to your coil winding diagram, it looks like you have two grounds so that’s why I’m asking this. Anyway, I thought I would just ask you I’m not so sure what’s wrong. It’s very obvious I have something wired up wrong. I also checked my grounding as well and it’s got a good ground. Also the 9 V battery is good to go, I checked the voltage on it to make sure.
Mike, so glad you did this video on varacter diodes. Did you try the power diodes back to back? Also on the single power diode setup, does changing R1 or C1 help at all? Just a thought. Thank you so much for the diagrams and illustrations!!!
You might consider using the base-collector junction of a power transistor. Perhaps the base-emitter junction since they have a lower breakdown voltage. They will not tune as linearly as a hyper abrupt varactor, but they may be available for free in your “junk” stock.
LOVE THE SIMPLE EXPLANATIONS on this channel. I kinda need some help w somthing if u can .. Im playing around with slayer exciter tesla coils but finding near impossible to get a power measurement because of stray hv/emi even with less than 9Vdc input
The best you can do without a screen room and lab equipment is to measure the DC input power (V X I) to your system and estimate your radiated power based on some (low) efficiency number as suggested by the design. Total Radiated energy is Electromagnetic, Static, Plasma, Light etc... combined?
Actually, just about any 400X diode would work. You might have to adjust your coil windings or put another capacitor in series with the 400X diode. The difference between a varactor and a standard diode is a varactor DIODE is made to be very linear and exacting. The idea behind a varactor is the fact that it is a SEMICONDUCTOR. It conducts electricity in one direction and acts like a GAP in the wire in the other. Between any gap in metallic surfaces, you have capacitance. When you reverse the bias of a varactor diode, you effectively increase the "gap" between the P and N junctions of the silicon diode. Varactors are designed to be extremely linear to be used for tuning circuits. One use for varactors is in VCO, or Voltage Controlled Oscillator portion of a phase locked loop circuit. This is how CB radios can tune 40 channels over a 450Khz band with just one crystal. Technically 80 channels as there is a 455Khz offset between the transmit and receive frequencies within the radio itself. This is also how an FM radio can tune over a 200MHz band with NO crystals at all. Same with an AM radio over 630Khz. AM and FM radios don't need crystal control as they do not transmit. Some older CB radios were modifiable using programming switches to achieve over 200 channels into bands where they didn't belong. So called "export" radios can navigate 10Mhz with only one or two crystals. These are controlled by a microprocessor but these still use a varactor controlled VCO circuit to keep the channels on frequency. It is popular with some ham operators to modify CB radios to transmit in the 10 meter FM ham band 29.000Mhz through 29.700Mhz. This is legal ONLY if you have an amateur radio license at least in the U.S. Zener diodes won't work well because they are designed to "break down" at a set voltage. If you want to use a Zener, use one with a high break down voltage. Depending on it's set voltage, it should give you more range.
Geesh i remember building this old stuff. Ingenious. My antenna stretched across a 8 acre field. Probably 1200 feet long. Now! Lets figure out a gravity wave detector for communication. Lets get this info out to the public.
Amusing, but was hoping to aspire some to higher knowledge. 3 top scientist have already been executed for their discoveries. Civilization has already been contacted. Its very simple try people!
Wonder what would happen if 4 varactor diodes were connected in some type of bridge configuration. My first xtal radio was a Cub Scout radio with a catwhisker and galena rock.
How are you managing to create such lovely diagrams. I have used AutoCad in the past but it is not really for circuit diagrams. I do draw quite a lot of diagrams for work.
I was going to ask about parallel varactors but you ended up mentioning it at the end of the video... Have you found any good surplus sites with varactors? I don't think NTE is around any more (which is a shame, I used them a lot back in my TV,VCR,Radio repair days...) Cheers,
@@MIKROWAVE1 SMBJ12CA - 1nF on 0V. But capacitance range is not wide - 650pF on 12V. Also Schottky diode SS54C - 570pF on 0V, 140pF on 20V. For my project that was enough, but for radio... :( But You must try some high voltage suppressors.
Can you replace a variable capacitor with a varactor in a superhet ?I know in superhet you have two capacitors ,one for the tuning and the other for the oscilator ..
Yes this is doable as long as the diodes are fairly identical curves and the IF Frequency is no more than a reasonable percentage of the tuning range, you should be able to scale the offset tracking with one potentiometer tuning voltage source.
Michael, I did not do too much with the alternates. Just enough to tease some thoughts. I think that 3D printing will bring some interesting ideas with many radio projects.
Good point Tomy. I do try to accomodate folks that ask questions in and comment in other languages, in a primitive way using Google Translate etc..But I should also provide the english as well.
Since you need to use a battery to power the varactors, you might go one step farther and replace the diode detector with an infinite-impedance detector (IID). The advantages of using an IID: You don't need to tap down on the coil. This will give you greater output voltage gain. It doesn't decrease the Q of the tuned coil giving you greater selectivity. You get true envelope detection with little garble. All this should give you greater sensitivity as well. With the greater gain, you might be able to use the less sensitive high impedance headphones.
Agree and adding bias has brought great shame to me already. :) Certainly, other more efficient topologies and positive features are available with three terminal devices.
I think - varicap tuned crystal radio loss "crystal radio spirit" For crystal radio can use variable inductors, variometers... If use external supply, better made TRF receivers, reflex receivers... ( better sensitivity, selectivity, ferrite loopstick antenna ).
Of course not. A crystal radio is when you make a detector out of a razor blade and safety pin or a galena rock and wind your coil on a hockey stick from wire recovered from a Model A Generator, form your variable capacitor from a pair of metal cigar boxes and wax paper and make your own headphones from a pair of old telephone handsets!
I always wondered if the VVC would work for tuning. They would obviously, but did they. Something about radio gods being unhappy or some such. Put in a nice wooden box with stain and lac bug, you wouldn't know. Not cheating if no battery powers the detector right? Speaking of mechanical caps. I am looking for the old 270 degree cap that would like to enjoy its retirement comfortably and not in a landfill. People call me crazy, ain't no such thing they say. Seen the ads and pics. And the old grungey, tarnished brass monster looks like it needs 2 months of spa days. I know someone who can take that junque and turn it back into the mechanical and visual art it was. Revived an exploded Arc 5 cap. 5 plates of metal, loose stack of thin cards, bunches of tiny balls, and gears. Just saying. Decaffe. Definately decaffe.
All entertainment sites like mine cheat. Ha. If it helps, can I suggest that the early professional crystal sets always used bias to improve the sensitivity of the crystal? Carborundum etc...
I did not introduce 2 dollar 12V solar power solution and rechargeable 9V battery that I got hold of. Ha. These little 4x4" panels are made in mass quantities for those outdoor lights.
Without a doubt, my favorite crystal radio video. Excellent content and quality work. Thanks Mike...
Mike, I can only thank you for putting up such a lovely set of very informative videos about radio and using tubes and semiconductors. I hope you can do many more. Balanced modulators etc. and phase locked loops. One of the most down to earth real radio hams I have ever seen. Just wonderful and I am learning loads even though I already have a degree in electronics from Oxford. Please make more.
Wow thanks Allister. The University of Oxford is really, tops and old! It goes back way before valves; 1096 I think! I'm not saying you are old...
OK.. The use of a Varactor in place of an "Old School Plate Capacitor" gives me an Idea to use one to tune a Frame Loop Antenna.. Easy to feed a Variable voltage rather than trying to control a
Servo Motor to move the "Physical" Capacitor Plates.. 👍👨🎓Thanks for Posting 73s
When I was a very young kid building my first crystal set I was so impressed it worked when I hooked the ground wire to a water pipe. Could not understand that the ground was a big part of it's operation. Thanks for your vids. Carl, AB1ZI
Thanks for watching Carl. I think I would my first crystal radio coil on a chunk of Hockey Stick!
I ordered one of the NTE618 varactor diodes from Amazon immediately after watching your video. I received it today and incorporated it into the circuit using your ferrite rod receiver - "Spare The Rod? Spoil the Crystal Set". The varactor works very well with the ferrite rod. I am really impressed with the performance of the varactor diode. There's a big hole in the prototype where the 365 pF cap used to be. The NTE618 diode is tiny but its performance is huge. I have a lot of tests to perform. I'm going to see what range I'm getting. I have a signal generator I can use to test the range. Most of the stations come in in the upper portion of the band where the voltage on the varactor is at 1.5. volts or less. I'll do more tests and report more later.
Wow Fantastic! Sounds like you need a few more turns on the rod to center up the band a bit.
If only you were nearer. I could learn so much. Your knowledge is astounding.
Get closer to the screen. Ha. Thanks for watching!
This was both useful and interesting. I need to watch it again to take it all into my geriatric mind! I'm guessing purists would say you can't have batteries in a crystal set but it's certainly a good alternative to mechanical capacitors.
They had better, since "I am spoiling the singular feature: freedom from a power source, which is the very essence and magic of the crystal set"
@@MIKROWAVE1 You plan to drive it from solar energy might part redeem you! LOL
@@acestudioscouk-Ace-G0ACE I remain unredeemable with such a gaf!
@@MIKROWAVE1 Surely not, I'm sure the wire winding Wizard will look kindly on you and they will keep your place in Crystal Set Heaven! LOL
I have not tried Varactor tuning for the BCB but I do use it for tuning my 40M DC receiver with a pair of 1N914 switching diodes in parallel and it tunes 15 KHz ( 7.029 to 7.045 ) of the portion that I normally listen to. I loved the Book Condensers used in the 1920's Crosly radios in my collection years ago 🙂
I used to get police calls off our wall phone in Detroit on a cheap transistor radio. Picking up their "IF" at 1650 - 1750 MHz? I wonder what an audio taper pot. would do for the band spread here? I like that Varactor Tuner idea.
I did not see the audio taper idea helping the "real varactors", but it might work on some diode curves. I did not say myth on purpose.
Excellent! Ive seen those linear shaped capacitors before and always wondered why they were shaped that way, stunningly obvious when you point it out. PS my background is not radio, its dc or digital stuff :)
Well you are in luck because radio is mostly digital nowadays!
Great video.
I would have liked to see additional testing with MOSFETs and leds but what you did was awesome.
Looking at the special variable cap you had made me think about making a cap using PC boards and shaping them in a similar way to linearize them.
Fooling with crystal radios will never die out!
I really admire you skill and knowledge.
I am recollecting my many past mistakes!
Can you make a nice simple veriometer setup? Would love to see this in a crystal circuit of yours. Perhaps this will give you a wider range in your varactor radio too. Keep up the great work!
Seems like a natural for 3D printing, but it could be done with a square armature and stator winding.
Thank you. You do things differently to all the other videos on varactors that I have seen so far.
What I loved was that you put in different diodes and compared.
That is brilliant teaching 👏 😀.
I am getting a feel for the varactor now.
Thank you so much. You are what makes the Internet a gift for everyone else.
You also empower people like me.
Thank you.
Truthfully this was discovery for me so I started from scratch. Its important to enter a new area without a soluton, and do a bit of research.
@@MIKROWAVE1 I am trying to build a monophonic synthesizer with the designs from other people but I want to understand what every component does. Eventually I want to design my own.
Sometimes electronic components are used unconventionaly and can throw me.
You did a stellar job in explaining this.
Again thank you.
You may not realise it but your teaching also gives me the confidence to try and try again. So ,just thought you should know that.
Very helpful thank you. I found this video just when I was wondering where I was going to find a decent source for tuning capacitors for my home projects.
I did the same nonsense, but I am proud myself as you should. Thanks for your fantastic information.
Mike, thanks for another great video and for investigating a wide range of devices and configurations.
As a regulator, for accuracy a Zener has to pass significant reverse current. It seems unsurprising that, when instead it's used as a varactor with a similar applied voltage, it loads the tuned circuit. TBH I wasn't expecting the Zener to work even as well as it did.
Hello! Good work! I made several experiments with a crystal radio and made some conclusions. The crystal radio has a good sensitivity when we have high quality factor of input LC resonance circuit. There can be a variable inductor (a ferite road is a good choice ) and there can`t be a variable capacitor - because it decreases quality factor. Next - you can`t shunt an input resonant circuit (a coil and an antenna): because quality also will be increased. As a very good solution - you can use a RF mosfet: for example BF998 (with connected gates 1 and 2 in parallel ) as a synchronous switch.Connect gate(s) to the hot wire of a coil (i.e. an antenna), source to 1/4 part of a coil, drain - to an RF blocking capacitor to a ground (common). You can use 250 Ohm small earphone but it can be connected through an electrolytic capacitor to drain. I had an excellent results - this crystal radio receives a noise of AC current from AC main in a village. I had an antenna - 15meters of wire with feeder that had been connected to middle of antenna . You can much improve selectivity wen you use an additional LC circuit with a 68pF capacitor .
The old single gate 3N128 which is unobtanium was a wonderful Mosfet. But yes you can tie the gates together!
Your video answers a lot of questions I had about crystal radios. Thanks
This is a nice video, great comparison between the diode types. I just used a varactor diode in a receiving only antenna system to tune it across the bands, and it works really well, thanks for the confidence boost to get me motivated.
You almost don't need a switch on the bias supply for the varactor. The max leakage current is 100 nA and a 50K pot would give you 180 uA. You might even be able to generate your bias supply off the antenna with a voltage doubler detector. I am impressed as well.
I think you just put the 365 pF variable capacitor guys out of business. I am really impressed.
Very True on the current drain! I bought a 12V solar pack for 2 bucks that I was going to introduce, but I will save that for another video.
You are truly blessed. You must live in an " RF " mute zone. Anything you build tunes in numerous stations, and they all sound as if FM quality. However, I would like to know what you are using for a long wire antenna, and its length. I ( on the other hand ) live in a Microwave. Extreme amount of noise on everything, even with top modern day receivers, extreme amounts of noise. I have built replicas of your crystal receivers, and have yet to receive anything but crackles, pops, and noise. I do like the varac diode receivers, and just for the fun, am going to build one. Who knows, maybe this one will work. Great work on you part, very knowledgeable. Keep up the great work. Jim
awesome pictures of the angle inductor tuning. thats way neater than the old typical gang-cap. 73 N9IZX
Varicaps are hard to find these days. As are tunnel diodes.
Instead of varicaps I used LEDs. The older types, greenish yellow were the most suitable for this application.
Enjoyed and enjoy 🤝🏻👍🏻🇳🇱
Workarounds and Tricks like this are great fun, but it depends on how much Q you need, and the application. I have been able to find all kinds of Varactors lately. Thanks for watching!
You can power the varactor diode by tuning in a local high power radio station and rectifying and filtering its output. A UA-cam contributor (W1VLF) generated 27 volts at considerable power using that technique.
Blessing and a curse being that close to a high power station I guess!
Thank you Mike. Very interesting and always appreciate your videos.
Thanks for watching Steve.
I want to drive the varactor with a sawtooth waveform. I would then feed the recovered carrier to a scope as a sort of primitive spectrum analyzer. I could optimize the receiver for each station I wanted to receive. That would be great fun.
you are a happy guy:)
here in Germany nearly all am transmitters are out of service.
best 73 and thx!
Ah Yes Antique Modulation. Well lets add a BFO and tune it to 630M.
This is really a cool video. The Remco looked cool but the rocket radio was the best. It had a ferrite inside a much smaller coil. I once made a crystal FM receiver, no batteries, 1N82A,
it only received 2 stations but it had a very short antenna. I could hold it up in the air and
pick up the signal. There was a fair amount of distortion because it didn't have a true FM de modulator but it did work.
To be a "real crystal set" you need to get rid of that battery. You could do it by having other diodes going to a large cap creating a power supply from the RF depending on the needs of the varactor. I saw one once where the RF power ran a transistor amplification stage, no batteries. It was in an old book "101 Electronic Projects". If I did a design today I would
start by picking the strongest station and set up a crystal set as a power section tuned to that station, (might not need rectifying ) rectify the output then go to a buck boost section to get the voltage up. I would also try to design the varactors so that they used the lowest possible voltage.
Do you remember the CK722? They had a can with a glass base, the can rusted. I believe it was the first transistor a mere mortal could buy.
Wow, I checked ebay for varable caps and some were 70-80 bucks! I have a big box full of them out in the barn. Thanks a lot.
Keep up the good work!
Wow! With a local station as the power supply into a cmos 555 voltage tripler and an 8V LDO.
@@MIKROWAVE1 You are right! It would need to be regulated or the scale would be all over the place.
Taking those steel shot, you can slam them with a sledge to make 2 opposing flat spots to make drilling them by hand possible. Good variable tap for your tuner.
Wow! That is some trick.
Wonderful demonstrations!
Thanks for watching!
Crosley used the "book" style variable capacitor in some of their early radios.
this turned out to be a very good video
Very interesting! I wonder if you could replace the battery with a supercapacitor and a hand crank to top it up?
Howdy.
Good information. I have been looking for some large value varactors for some time. I located 11 items of the NTE618 at TME and ordered them. Thanks for providing the type.
I would like to point out that using two varactors in anti series will reduce the max. capacitance to half the value. One may want to replace the upper varactor with a fixed cap of say 10 times the varactor max value. I.e. 4n7 or 5n6 plastic cap, or for best quality, cercap. Large cercap.s are available. Practically all varactor bandwidth will be available.
High regards.
Fantastic Information. This was an experiment and investigation. I had never considered varactors with crystal sets before.
@@MIKROWAVE1 Howdy again.
Thanks mate. I am happy to have contributed to a Brother in The Field of Detection.
Regards again.
Thanks Mike
I am thinking in a TRF teceiver this way
Amazing ... above all diy var cap
Hello Michael, great stuff as usual...! So I would love to see a TRF preselector using "ganged" varactors. These dual gang TRF air variable capacitors are expensive and I expect many of us would benefit from doing the job with varactors... that would be a fantastic...! Thank You, Michael...!
That sounds like a worthwhile video!
That sounds great...! Best regards, Greg KC9ZEW
Would have been nice to see the use of more modern varactors with greater linearity. Something like an NXP low voltage BB201 dual diode common cathode device that is much cheaper than the going obsolete NTE618. Great video. You've also explained why my IN1007 based regen radio sucked so much with very little tunability. I'll switch out the IN1007 for proper varactors. [edit] The BB201 on Mouser are 83 cents in one off quantities and 73 cents for 10 or more.
Mouser has a great selection, unlike its competitor.
But I would incurr the wrath of the anti-SMD device faction.
@@MIKROWAVE1 Yeah, that did occur to me. All i'd do is buy SMD adapters but I guess each to his own.
The BB201 is not optimized for a.m. radio. The capacitance range is too small.
It might not be a bad idea to pick up a few NTE 618 just to have them on hand.
Excellent video thanks from England 🇬🇧
England? Well glad to have you watching!
Good video, thanks as always.
Thanks for watching Cory!
Great video, thank you for the clear explanation and for the practical tips too. Could this technique be used to remotely tune receive loop antennas ? Would it be posssible to have a variable bias T that could send a control voltage?
Definitely worth a try.
There will be feedback as folks try this. I already heard from one.
variable capacitor are very expansive. Varactor is the solution. I use in a VFO
Varactors are great all right. You do have to consider temperature changes with varactors.
The variometer designs are neat. Awesome examples! Amazing, the capabilities for the 3D printers... especially for metamaterial like designs and not only the parts of a design. Electroplating the 3D printed parts seem like another way also for more exotic designs. I've been wondering about stealth antennas for fox hunting using the sewing machine to stitch... I suppose kind of World War era design like. Thanks for sharing. Reminds me I wanted to check and see what the Cricut Expression I own now can cut in regards to sheet aluminum, brass and/or copper.... looks like a no go unless a foil on another plate medium. HHhmmm... wondering what the COTS CNC lasers can do without O2 or how many parts can be cut from a sheet in the most cost effective way if outsourced to a fab shop project way? Anyways... the digital components are neat and super practical for more automatic processes. Thanks for all the details and specs. as well!
@@lysippus I was jotting down my thoughts while watching the video, that's all there comic relief bot. I do wonder with the mind control... what the handlers come up with based on memory associations for cues, keys and triggers. Guessing they are liable for many of the head traumas over the years.
Excellent, very good vid. It has got my interest in 'crystal radio' again. Curious if forward biasing the detector diode will help the reception. Thanks 73.
It does, and really works well on schottky diodes like the BAT85.
Mike, I have a question for you about your dual veractic crystal radio. I recently built one and I made a circuit board to mount the components onto and I worked from your schematic diagram and made sure that everything is in order , but I have not been successful on getting it to work at all. So I am using a 10k potentiometer and in your opinion do you think maybe the potentiometer value is not high enough for it to function ? It doesn’t seem like it’s receiving anything. I’m going to try a 50 K potentiometer next. The next question I have do the primary and secondary grounds go together from each coil ? According to your coil winding diagram, it looks like you have two grounds so that’s why I’m asking this. Anyway, I thought I would just ask you I’m not so sure what’s wrong. It’s very obvious I have something wired up wrong. I also checked my grounding as well and it’s got a good ground. Also the 9 V battery is good to go, I checked the voltage on it to make sure.
Mike, so glad you did this video on varacter diodes. Did you try the power diodes back to back? Also on the single power diode setup, does changing R1 or C1 help at all? Just a thought. Thank you so much for the diagrams and illustrations!!!
The power diodes work, but they are very low C. And high res versions are on my FB Radio Resources support page.
You might consider using the base-collector junction of a power transistor. Perhaps the base-emitter junction since they have a lower breakdown voltage. They will not tune as linearly as a hyper abrupt varactor, but they may be available for free in your “junk” stock.
Or use a power MosFet.
Junk is good.
Hi Mike - Great video - I played around with some BB212 devices some years back. They look a lot like the 618 but with 2 in one package? - Jay
LOVE THE SIMPLE EXPLANATIONS on this channel. I kinda need some help w somthing if u can .. Im playing around with slayer exciter tesla coils but finding near impossible to get a power measurement because of stray hv/emi even with less than 9Vdc input
The best you can do without a screen room and lab equipment is to measure the DC input power (V X I) to your system and estimate your radiated power based on some (low) efficiency number as suggested by the design. Total Radiated energy is Electromagnetic, Static, Plasma, Light etc... combined?
Mike, please take a look at the 1N5817 and let us know if you think it would make a reasonable "Varactor" diode... Thank You...!
Actually a good detector with a bit of bias! But alas not a good candidate for a varactor on the AM bands.
Thanks Mike...! 73, Greg, KC9ZEW
Actually, just about any 400X diode would work. You might have to adjust your coil windings or put another capacitor in series with the 400X diode. The difference between a varactor and a standard diode is a varactor DIODE is made to be very linear and exacting.
The idea behind a varactor is the fact that it is a SEMICONDUCTOR. It conducts electricity in one direction and acts like a GAP in the wire in the other. Between any gap in metallic surfaces, you have capacitance. When you reverse the bias of a varactor diode, you effectively increase the "gap" between the P and N junctions of the silicon diode.
Varactors are designed to be extremely linear to be used for tuning circuits. One use for varactors is in VCO, or Voltage Controlled Oscillator portion of a phase locked loop circuit. This is how CB radios can tune 40 channels over a 450Khz band with just one crystal. Technically 80 channels as there is a 455Khz offset between the transmit and receive frequencies within the radio itself. This is also how an FM radio can tune over a 200MHz band with NO crystals at all. Same with an AM radio over 630Khz. AM and FM radios don't need crystal control as they do not transmit. Some older CB radios were modifiable using programming switches to achieve over 200 channels into bands where they didn't belong. So called "export" radios can navigate 10Mhz with only one or two crystals. These are controlled by a microprocessor but these still use a varactor controlled VCO circuit to keep the channels on frequency. It is popular with some ham operators to modify CB radios to transmit in the 10 meter FM ham band 29.000Mhz through 29.700Mhz. This is legal ONLY if you have an amateur radio license at least in the U.S.
Zener diodes won't work well because they are designed to "break down" at a set voltage. If you want to use a Zener, use one with a high break down voltage. Depending on it's set voltage, it should give you more range.
I think we need a Kitchin Regen with Varactor Tuning.
Geesh i remember building this old stuff. Ingenious. My antenna stretched across a 8 acre field. Probably 1200 feet long.
Now! Lets figure out a gravity wave detector for communication. Lets get this info out to the public.
Does this use apples in some way?
Are you calling the resonant frequency of the earth a gravity wave ?
@@MIKROWAVE1 - Homemade _apple battery_ to power the varactor?
It could be called the _iBat _
:D
@@EngineeringVignettes Apple Butter gives much smoother tuning! ;)
Amusing, but was hoping to aspire some to higher knowledge. 3 top scientist have already been executed for their discoveries. Civilization has already been contacted. Its very simple try people!
Wonder what would happen if 4 varactor diodes were connected in some type of bridge configuration. My first xtal radio was a Cub Scout radio with a catwhisker and galena rock.
You have gone BEYOND THE IMPOSSIBLE! Ha . Dunno but someone will have heard of it.
Super radio
Tk for
Your Nice vidéos on4kmc Best 73
Thank you for watching! 73's WU2D
Interesting topic, but I've found they introduce non linear interference, a bit like a broadband tuner. Nothing beat copper and a proper capacitor.
Not the point of the vid, but agree of course. You could hear intermod when I brought my generator up as a strong interferer with a station tuned in.
What kind of pot are you using, would an audio taper provide a more linear dial ?
What about a 20 turn Pot+a Vernier scale + 5x9V batteries.
The absolute max voltage is 16 volts. You could still have a 20 turn pot with a 9V battery.
@@benthere8051 VHF Veractors require between 0.5-50V for tuning.
How are you managing to create such lovely diagrams. I have used AutoCad in the past but it is not really for circuit diagrams. I do draw quite a lot of diagrams for work.
It's pure art on an illustration program, so any style, any era is possible once you create your own symbols.
@@MIKROWAVE1 Hi Mike but is it Adobe photo shop or what software?. I have Visio and find that hard work.
Stand By Varaction!
Giggling here.
I was going to ask about parallel varactors but you ended up mentioning it at the end of the video...
Have you found any good surplus sites with varactors?
I don't think NTE is around any more (which is a shame, I used them a lot back in my TV,VCR,Radio repair days...)
Cheers,
NTE is alive and very well. www.nteinc.com/
NTE parts are readily available at Amazon.
That's great Mike.. Is that a LOG or LIN pot? I am assuming LIN...
Yes a 50K Linear Pot.
Power suppressors can have capacity up to and more than 1nF
And you can bias them? Please suggest a part number of an example device.
@@MIKROWAVE1 SMBJ12CA - 1nF on 0V. But capacitance range is not wide - 650pF on 12V.
Also Schottky diode SS54C - 570pF on 0V, 140pF on 20V.
For my project that was enough, but for radio... :(
But You must try some high voltage suppressors.
Can you replace a variable capacitor with a varactor in a superhet ?I know in superhet you have two capacitors ,one for the tuning and the other for the oscilator ..
Yes this is doable as long as the diodes are fairly identical curves and the IF Frequency is no more than a reasonable percentage of the tuning range, you should be able to scale the offset tracking with one potentiometer tuning voltage source.
One more thought, along with my other two comments: did you try a power diode and a zener back to back?
Michael, I did not do too much with the alternates. Just enough to tease some thoughts. I think that 3D printing will bring some interesting ideas with many radio projects.
Yes we want everyone to understand what we sayin so only English cuz its a universal language
Good point Tomy. I do try to accomodate folks that ask questions in and comment in other languages, in a primitive way using Google Translate etc..But I should also provide the english as well.
Since you need to use a battery to power the varactors, you might go one step farther and replace the diode detector with an infinite-impedance detector (IID).
The advantages of using an IID:
You don't need to tap down on the coil. This will give you greater output voltage gain.
It doesn't decrease the Q of the tuned coil giving you greater selectivity.
You get true envelope detection with little garble.
All this should give you greater sensitivity as well. With the greater gain, you might be able to use the less sensitive high impedance headphones.
Agree and adding bias has brought great shame to me already. :) Certainly, other more efficient topologies and positive features are available with three terminal devices.
Thanks for solving a difficult problem. KB1FRP, 73
Mike can we use a variable ferrite coil as an antenna loading coil?
Done on many portable setups like my WW2 MAB. It has an adjustable center loading coil where you just push and pull the ferrite slug to resonate.
I think - varicap tuned crystal radio loss "crystal radio spirit"
For crystal radio can use variable inductors, variometers...
If use external supply, better made TRF receivers, reflex receivers... ( better sensitivity, selectivity, ferrite loopstick antenna ).
Excellent Ingus. Keep up the radio building.
@@MIKROWAVE1 Thanks!
Is it still a crystal radio if you need a battery to run it ? And why
Of course not. A crystal radio is when you make a detector out of a razor blade and safety pin or a galena rock and wind your coil on a hockey stick from wire recovered from a Model A Generator, form your variable capacitor from a pair of metal cigar boxes and wax paper and make your own headphones from a pair of old telephone handsets!
I always wondered if the VVC would work for tuning. They would obviously, but did they. Something about radio gods being unhappy or some such. Put in a nice wooden box with stain and lac bug, you wouldn't know. Not cheating if no battery powers the detector right?
Speaking of mechanical caps. I am looking for the old 270 degree cap that would like to enjoy its retirement comfortably and not in a landfill. People call me crazy, ain't no such thing they say. Seen the ads and pics.
And the old grungey, tarnished brass monster looks like it needs 2 months of spa days. I know someone who can take that junque and turn it back into the mechanical and visual art it was. Revived an exploded Arc 5 cap. 5 plates of metal, loose stack of thin cards, bunches of tiny balls, and gears. Just saying. Decaffe. Definately decaffe.
All entertainment sites like mine cheat. Ha. If it helps, can I suggest that the early professional crystal sets always used bias to improve the sensitivity of the crystal? Carborundum etc...
How about a REAL power diode, like a 50 amp stud mount diode!
How Studly! I can give it a try.
😏are we gonna be able to get that 9v. battery by the 'purists'?
I did not introduce 2 dollar 12V solar power solution and rechargeable 9V battery that I got hold of. Ha. These little 4x4" panels are made in mass quantities for those outdoor lights.
!=8)
The 1N4001 has max. 40pF at 0V. This is absolut useless.