Variable inductor crystal set drives a speaker
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- čas přidán 28. 10. 2020
- A simple crystal set using a variable inductor to select stations. Two fixed capacitors allow coverage of the AM broadcast band in two segments. See earlier video for more details on the inductor.
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I grew up with an inductive tuned crystal, was small rectangular and green,antenna was pulled up to tune . Got a Radio shack ,RIP, 50-1 and proceeded to build various radios and oscillator. I was very close to radio park on top of the 400 ridge over the valley with Birmingham. I could drive the small ( common to most 5-6 transistor radios) that came with it . I had a high horizontal line almost perfect for the max amplitude. Billy Green was seven years older , he strung my antenna and had done similar things as a kid, and living next door. Almost killed my self taking apart the TV they threw out. CRT Flyback was in good order and blew to the tube not my right hand . God has saved me so many times….😮
Back in my youth I had a crystal set which had a coil wound on about a 10mm former and was tuned by moving a metal rod plunger, with a dark grey cylinder attached, up or down inside the former. I didn't know anything about how they worked back then but I understand now that the dark grey cylinder would have been ferrite.
There are few considerations you need to think about.
1. Matching antenna to LC-tank circuit you have. You really want to have a good matching which means the most energy will be directed to the tank circuit.
2. The same thing for detector diode. You want to find the optimal way to tap the signal out of the selector.
3. Try modern Shottky diodes like BAT-46. Those have lower forward voltage drop and will have less loss. You can even build a full bridge rectifier that will allow to harvest more power.
4. Improve Q of the LC tank circuit. This can be done by making inductor using litz wire and having a larger diameter of the inductor.
A quick note about the impedance and the transformer.
This is a 240V to 10V transformer.
That means its turns ratio is 240/10=24:1
When you step down the voltage like that you also step up the current.
Resistance = Volts / Amps
so we end up with and impedance ratio of 24*24 = 598
The speaker is 8 Ohms natural impedance
8*598 = 4608Ohms
This is why it works like a high impedance headphone.
You can also get a crystal earphone from online hobby stores.
Sure, you can order whatever you want from Amazon or eBay. I really like the idea of being able to build a receiver with whatever is lying around, which I think is the point of this video.
@@johnwest7993 I commented for those just starting out and thus may not know about high impedance earphones.
Excuse the ignorance. Question, why does the transformer help the signal be Heard on a speaker rather than high impedance headphones? Because it steps up the current but I don't understand how it lowers impedance as well? Thank you in advance. I'm trying to build one and wow so much to take in!
@@brandonlaragirl Roughly
Z = V / I
Where Z=impedance, V=Voltage, I=Current
A transformer with a 2:1 turns ratio will have 1/2 the voltage on the secondary. If you draw current from the secondary, only half as much is need on the primary.
Thus going primary to secondary, voltage is divided by two while current is doubled
Z(secondary+) = (1/2V)/(2*I)
Thus Z(secondary) is 4 times lower
@@kensmith5694 awesome, thank you!
That's class, I was only messing around with a regen yesterday though I think your crystal set works better!!
WoW, when I built a crystal set I struggled to hear the earphone speaker let alone drive a speaker from it. Mind you i think I was 9 years old. I didn't have a clue how to get any more out of it. I think I only ever heard one station on it anyway, I was so far from anywhere!
Peter look up crosley book capacitor. It is a type of capacitor a home brewer could make pretty simply and it was used in the 1920s in a commercial radio in the United States. You would not want to replicate the dial shaft arrangement in order to make it rotary but you can adjust the capacitance just by opening and closing the sides. It's a variation of a compression capacitor.
Awesome! I might build one myself, using a long screw for fine adjustment of the inductance, like a dial.
From years.......you are my teacher........thank you......🌷🌷🌷🌷🌷🌷🌷🌷🌷🌷
Nice, you’ve built a simple variometer, didn’t know the tip about big speakers vs small ones that I’ve tried, my small speakers even with a transformer have been disappointing
Excellent video Peter . Antenna length and higher bands are possible. Thank you SeanZS5X
Very good useing a transformer to increase the Audio.Im still working on improving a Jaycar kitset I bought,so this has certainly helped.Thanks.
I think the biggest improvements you'll get are if you can optimise the tapping point of the diode and coupling from the antenna. Kits often have a compromise position that isn't best for your circumstances.
This is truly excellent! I subscribed!🌟🌟🌟🌟🌟🍻
Gold man.... thank you!
Really nice!
That's a pretty cool project :)
Excellent demonstration.
Please, would you mind powering the audio so we can hear it ?
i noticed on the RTL-SDR on diirect sampling the gain is 0 yet it picks HF no problem, the lower the frequency the more natural gain, i guess it comes to antenna aperture after all, with enought aperture you can drive speakers without amplification
Thanks!
Конденсатор забирает часть энергии.От него лучше отказаться,но добавить витков к катушке,через соединение типа много позиционный переключатель,для понижения принимаемых частот,при присоединении дополнительных витков.Звучание будет громче.
Thank you! Very good video. I still wonder if you could use it for an antenna tuner. Would there be too much loss on Tx? I wonder why manufacturers do not use variometers in the tuners. Is it because they are too complex mechanically?
I think a version with fewer turns would be fine for an antenna tuner. Variometers were widely used last century. I agree that mechanical complexity probably made manufacturers stop using them but not an issue for hobbyists, especially with 3D printing making custom parts easier to make.
Cool. Have you ever tried a 'foxhole radio'? The one with a pencil stump instead of a diode ;-)
Peter, have you tried using a speaker transformer from an old valve radio? BTW the ‘experts’ who say this wont work are WRONG! I have 50+ years of practical experience in this field.
Nice
What are you going to try next, Peter? Magnetic Amplification? Reactors? Vacuum tube x-rays?
X-rays are fun to play with if you know exactly what you're doing. if you do not they're dangerous as hell and you should not be toyed with.
He is going to built something to suck all the power from the radio transmitter to light his house lol.
Nice...........
Hi Peter, what size antenna did you use?
About 30m of wire, maximum height 11m up but most lower.
You certainly have a very very long antenna and a strong radio signal
👍👏👏
I should build a crystal set using the transformer impeadance match idea I got old 9 volt plugback will try driving stereo headphones, would 40mm PVC pipe and Cat5 cable wire making a tapped coil say 80mm long with tap ever 10 turns will work, magnet wire very hard to get now days ??
That should be OK. But if possible I'd use thicker wire eg from an old power extension cable.
@@vk3ye I do have a 10 to 470pf varible cap
I have had good luck using a single strand of cat wire. 24 gauge. I always wind 57 turns on a 3.25" diameter PVC pipe. You can use different diameters by consulting "Professor Coyle" online. The described coil uses 49 feet of wire. 24 gauge cat wire gives you about 27 turns per inch.
So why does increasing the capacitance let the radio receive higher-end am band. By increasing the capacitance you're also increasing the inductance? Thank you in advance
Higher capacitance with a given inductance allows tuning in of LOWER frequencies.
@@vk3ye awesome, thank you. Gonna work on building an amp today. Got a 386 and a transformer. Question! Is it better to use AC or DC current to power the amp.
if you kindly mention height and length of antenna wire?
About 20-30 m would do it.
@@vk3ye Thank you.
@@vk3yeI am more interested in utilizing H-field instead of noisy E-field. So I designed earlier a magnetic loop antenna on an X frame of wood. Each corner was 24 inches away from its nearest corners. I used audio speaker wire with 11 turns and a gang variable capacitor of 365pF in parallel to this loop antenna. There was 2mm gap between each turn of the loop antenna to cater for stray capacitance. One day the back of my hand touched the metallic plates of the gang cap and I felt induction and shock. So I used my gauss meter to check and it was detecting the induction. I have an idea to design crystal radio and place it near the same loop antenna instead of connecting a 20m long ant wire. At the output side I am intending to use ultra low power buck boost converter like LT3108 with a step up transformer to harvest maximum energy out of it. Of course I'll use good earthing. If you kindly give your comment or any guideline on this idea. I shall be grateful.
Circuit diagram at 5:39 minute.
Variometer like a "loose coupler coil"
I made similar variometer for LW band....
Technically this will not work. Your dealing with Uv. Millionths. Of a volt. Feeding that extremely low voltage and virtually no I= current in Ua. Micro amps the transformer would basically ground out a signal at that amplitude! I am a electronics Technician with a lot of engineering behind me . THIS WILL NOT WORK!!
Nonsense.
Yeah, I can tell you left the knowledge behind you
I had two E.T.s tell me I couldn't hear what I was listening to.
A high degree of knowkedge / education doesn't always equal wisdom.
I honestly doubt this setup works. Actually it cannot work ! It's easy to make something that appears to work and making it work by cheating .
Nonsense.
@@vk3ye i agree
Anyone who ever messed with crystal radios knows it works without any power. It's amazing when you make one yourself
@@vk3yeI just love it when someins is shown something that's working and they deny it works. lol
Thanks!