Author Topic: Crystal Radio Breadboard - Zero Sound  (Read 7164 times)

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Offline t1dTopic starter

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #25 on: December 20, 2018, 07:04:48 pm »
Sure,

The reason why the mag loop may be advantageous for you is the lack of need for a ground, its fairly self contained. Properly made one can develop a lot of signal. Definitely enough for a crystal radio.

Google "magnetic loop" (or especially "Magnetic loop calculator".)

Do you have any large pieces of cardboard or similar? What is ideal is something large and flat and square which you can cut up a bit. Also get another cardboard box large enough to serve as your stand for the first, (holding it up and on its edge vertically). 

Take the large piece of cardboard and cut two small notches around two or three inches on the side of each corner.  Use them to hold your turns of wire.

This loop will be the inductor and you put your capacitor in series/parallel with it to make a strongly resonant circuit.

Take your additional cardboard box and slice a single slice through it halfway so you can use it as a stand for your cardboard loop, making it easy to rotate by hand.

Then couple your detector circuit to it with a smaller pickup loop.

This will at least be able to show you if your other circuit works. (You don't need a ground or long wire to get a strong signal, you'll have to tune the antenna exactly to the station with your cap. The tuning may have to be very precise or you may miss the peak. Adding as large a knob as you can find will be helpful in doing this.)

Then you can try the traditional crystal radio.

For AM broadcast band you'll do much better if you can somehow get your antenna outdoors and up a bit. Also use a cold water pipe as your ground.


Sometimes... just sometimes... it is very good to not be married... For grins, I hung the antenna, in the house... Started in the rear bedroom, atop a bar stool. Down the hall to a coat hanger hung on the laundry door. To a bar stool in the den. To my lab desk in one corner of the kitchen. LOL... Maybe 65 feet?

I obtained a good amplitude of background hiss. Its frequency varied with changes in the v cap. However, I did not locate the 710AM station with either the original 120uH inductor, or a 330uH inductor (that tested as .29mH.) I hope to have complete success, once I learn how to calculate the needed inductor value...

The cat was only slightly curious as to what in tar nation was going on...
Thanks for this. I think I am catching on. It should be fun to try...
 

Offline t1dTopic starter

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #26 on: December 20, 2018, 07:06:45 pm »
Here is my am crystal loop radio. It uses just the wire coil as the antenna with a secondary coil driving the circuit of just a diode, x-tal earpiece, and the air variable cap. I would consider this as portable and quite packable if the loop could be folded and collapsed. Also consider that a loop antenna is directional, so you get better tuning and less noise. I was really impressed with the performance of this system. I picked up 18 stations...

Some earlier experimentation on the bench - same circuit but with a wire antenna and ground, and the smaller "traditional" air coils in the back. I've used a plastic spray paint can cap and a clear plastic pill bottle here. You might be able to test materials in the microwave for any RF heating - which is bad for a coil form as that indicates loss.

cdev mentions Q and that is quality factor and is related to loss. Higher Q coils (lower loss) are made with different winding techniques and material construction. One example is the use of litz wire to make the coil. Litz wire is a bundle of very small strands of wire that are insulated from each other. You can use a wire made up of 600 or more individual strands. The reason is RF moves on the outside and increasing the strand count increases the surface area of the wires, thus reducing resistance and loss.



My favorite design:
http://www.crystalradio.net/crystalsets/lyonodyne/index.shtml
Good information... Thank you for your efforts to post the pictures. Cool design...
 

Offline cdev

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #27 on: December 20, 2018, 07:11:54 pm »
Shortwave signals may only be audible at night, but they will fill the bands at higher frequencies than AM (fewer turns required)
"What the large print giveth, the small print taketh away."
 

Offline t1dTopic starter

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #28 on: December 20, 2018, 07:17:48 pm »
Shortwave signals may only be audible at night, but they will fill the bands at higher frequencies than AM (fewer turns required)
Shortwave? Excellent.
 

Offline cdev

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #29 on: December 20, 2018, 07:22:39 pm »
The only SW signals I would definitely be sure would likely be that strong if you are in the US are the bible thumpers and Radio Havana. neither are that interesting to listen to, unfortunately.

But who knows, you may get lucky. It's unpredictable and based on your antenna and where it is, and band conditions and I would expect even the diode you use.

Make sure you turn the loop around to try different directions as it is very directional, especially the null.

Are you sure the diode is a 1n34? If you have a diode tester - test it.
« Last Edit: December 20, 2018, 07:24:42 pm by cdev »
"What the large print giveth, the small print taketh away."
 

Offline chris_leyson

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #30 on: December 20, 2018, 08:45:23 pm »
I remember as a kid sitting for hours reading an old science book on my dads bookshelf, Science for the Citizen by Lancelot Hogben. "Dad, I want to build a crystal radio" so next weekend of we go to L.H.Evans in Cardiff market and buy all of the required parts. A 350pF film tuning cap, a Denco coil, an OA47 and a crystal earpiece. Wow that was fun and it worked reasonably well with a 50' long wire. I didn't have any luck building a single valve super regen but 50 years later I might have another stab at it just for fun. L.H.Evans is still there in Cardiff market and A simple crystal radio was the "spark" that got me into electronics.
 
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Offline StillTrying

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #31 on: December 20, 2018, 10:06:32 pm »
Anyway to check that the variable cap connections actually vary 20pF to 330pF.

With a DVM in place of the earphone you should see a few mV DC on a strong station at least.

With a scope you could ping the tuned circuit to see if it rings at ~700kHz.
.  That took much longer than I thought it would.
 

Offline metrologist

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #32 on: December 21, 2018, 12:56:49 am »
With a scope you could ping the tuned circuit to see if it rings at ~700kHz.

How do you ping?
 

Offline t1dTopic starter

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #33 on: December 21, 2018, 01:52:41 am »
The diode is a 1N34A, from a proper Crystal Radio supplier. I did proof it.
The v cap is also from a proper Crystal Radio supplier. I did proof it.
To ping the signal... Replace the antenna with a Function Generator and listen to the radio, for tone?
Thanks
 

Online vk6zgo

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #34 on: December 21, 2018, 03:15:25 am »
The diode is a 1N34A, from a proper Crystal Radio supplier. I did proof it.
The v cap is also from a proper Crystal Radio supplier. I did proof it.
To ping the signal... Replace the antenna with a Function Generator and listen to the radio, for tone?
Thanks

Do you have a function generator?
If so, you can couple its output very loosely to the Crystal radio  & tune across the range of frequencies you expect to be receiving.

Most function generators go up to 1MHz, so, with the gen set to sinewaves, as you tune across the LC tuning circuits expected resonant frequency, you should hear the background hiss suddenly drop, as the unmodulated carrier from the FG passes the actual frequency of resonance.
As there is no modulation, you won't hear any tone.

To actually hear a tone, try a square wave or sawtooth at around 1kHz.
Such waveforms are rich in harmonics, which the radio will see as a MF carrier pulsed at 1kHz----near enough to AM!!

Again---- put the tiny little RF chokes back in the parts bin, & wind a proper coil.
If you look at enough websites*, you should get a good idea of the number of turns on a given sized form.
 
As to not always needing an antenna, this is "sort of" correct.
If you have an earth connection to a metal water pipe, the radio will "use the earth as an antenna".

Another old time trick was to clip a short antenna lead to the metal of an old style dial phone.
This would capacitive lay couple to the phone wires.

Millions of kids over many decades made Crystal sets that "worked".
Making really good ones is a specialist hobby, but you might be best to stick with basics first.

* PS----take a look at this:-
http://www.techlib.com/electronics/crystal.html
« Last Edit: December 21, 2018, 03:46:37 am by vk6zgo »
 

Offline spec

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #35 on: December 21, 2018, 04:01:10 am »
Hi t1d

Check

[1] earpiece by connecting it to an audio source
[2} diode, especially back to front ratio (use 1V5 battery, 10k resistor in series and multimeter set to uA range).

The antenna matching will be rather poor with that circuit and the antenna reactances, both capacitive and inductive, will pull the resonant frequency all over the place.
« Last Edit: December 21, 2018, 04:09:15 am by spec »
 

Offline james_s

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #36 on: December 21, 2018, 06:03:03 am »
I remember building a crystal radio kit when I was a kid. As I recall there was no background noise, I only got anything when I tuned a strong enough signal. It needed a good solid ground and a long wire antenna to work at all.
 

Offline mikerj

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #37 on: December 21, 2018, 11:03:23 am »
I remember as a kid sitting for hours reading an old science book on my dads bookshelf, Science for the Citizen by Lancelot Hogben. "Dad, I want to build a crystal radio" so next weekend of we go to L.H.Evans in Cardiff market and buy all of the required parts. A 350pF film tuning cap, a Denco coil, an OA47 and a crystal earpiece. Wow that was fun and it worked reasonably well with a 50' long wire. I didn't have any luck building a single valve super regen but 50 years later I might have another stab at it just for fun. L.H.Evans is still there in Cardiff market and A simple crystal radio was the "spark" that got me into electronics.

Pretty much the same here, though I was given a Ladybird book "Making a Transistor Radio" which started with a crystal set and expanded it a regenerative design with speaker output.

I remember the crystal set not working very until I grounded it on a water pipe and local stations were then loud enough to hear clearly without putting the earpiece in your ear.
« Last Edit: December 21, 2018, 11:04:58 am by mikerj »
 

Offline StillTrying

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #38 on: December 21, 2018, 12:35:38 pm »
With a scope you could ping the tuned circuit to see if it rings at ~700kHz.
How do you ping?

Flick a 1V5 battery across the coil circuit through a 470R. In a simulation with 300uH, 165pF + 20pF scope, the ringing is ~650kHz which is about right.

As in the very first post, the RC time of 10n + 82k is too long. yellow
The recommended 1n + 82k gives a much better output. blue
« Last Edit: December 21, 2018, 12:38:42 pm by StillTrying »
.  That took much longer than I thought it would.
 

Offline Zero999

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #39 on: December 21, 2018, 04:28:33 pm »
Shortwave signals may only be audible at night, but they will fill the bands at higher frequencies than AM (fewer turns required)
I thought that short wave is mostly single side band, which can't be picked up with a diode detector?
 

Offline metrologist

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #40 on: December 21, 2018, 07:03:56 pm »
I think AM is more common for commercial shortwave broadcast. Voice comms typically use SSB.
 

Offline iMo

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #41 on: December 21, 2018, 08:19:03 pm »
99% of the short wave AM broadcast stations were switched off already..
The crystal radios were popular many decades back (1920-1990) in times the strong local stations existed...
As a child I took a Ge diode, old 4kohm headphones, a few meters of wire and got a perfect loud signal. Added a transistor, 4k/4ohm transformer and a speaker and I was pretty happy.
The trick was the 50-500kW AM sw broadcast stations were "on 24x7" and almost everywhere across Europe (almost every larger town had its own, mine 100kW one at ~1300kHz was about 10km off my home).
Today you have to watch the exact 1-2hours long broadcast schedule of the few stations of interest left, and use a quality sw radio with a decent antenna :)
« Last Edit: December 21, 2018, 08:53:06 pm by imo »
Readers discretion is advised..
 

Offline chris_leyson

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #42 on: December 21, 2018, 08:53:01 pm »
Link to a kist of SW broadcast bands https://www.short-wave.info/index.php?feature=frequencies
Picked up Radio Romania International on the 49m band whilst playing with an EMC test receiver the other day, also found an asian station, might have been Chinese, on 31m coming in at 100dBuV, that's 100mV at the 50\$\Omega\$ input with only 6' unmatched wire antenna. Test receiver has developed another fault however but the SW broadcast bands are still quite active.
 

Offline cdev

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Re: Crystal Radio Breadboard - Zero Sound
« Reply #43 on: December 23, 2018, 06:57:31 pm »
The cheapest shortwave radio that can be bought today is an RTLSDR blog version 3 USB dongle set to direct sampling mode. They are multiple generations of community refined improvements.  It has to be used with a computer but will offer endless radio-related entertainment. they cost around $25 and will still require your learning a fair amount of stuff and installing drivers to use it. Once you figure out how to use it you can find COTS dongles for under $10 and build them into circuits yourself. For HF pins 4+5 - the unused Q input on the RTL chip are a differential input which is very sensitive to HF, but you need an antialiasing (low pass) filter and ESD protection. Also soldering to the pins is difficult, but if you dont care about VHF you can use the 1+2 I input and solder to capacitors instead. Much easier.

That will be much better than a crystal radio. You could use a loop antenna if you built one for this project, that would work really great, plus be kind of visual, so much easier to tune.

A very high tech improvement on the crystal radio.
"What the large print giveth, the small print taketh away."
 


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