Crystal Radio Breadboard - Zero Sound

[t1d]

I breadboarded this circuit. I have zero sound, not even background sizzle.

- All components are of decent grade and proofed. Most came from a Crystal Radio parts house. I understand that a new earphone can be "jammed," but this one is sounding on a known source.

- All connections have proven connectivity, point-to-point.

- The ground is solid and is to Earth.

- The antenna is double strand zip cord of long length, maybe 50+ feet. However, I have not strung it out; it is still on the spool. Each strand is soldered in parallel. This should give good volume.

- The diode is germanium; 1N34A.

- There are local stations.

- I am using a 0-335pF variable capacitor; Pin #1 and GND. Data Sheet Attached. It operates CCW, but this is of no operational consequence.

- I have varied the direction of the diode with no improvement.

- I did not have a 0.001uF smoothing cap, so I used a 0.01uF cap. I have removed it from the circuit, with no improvement.

I have reviewed the circuit and, if there is an error, I just can't see it. So, your help, please and thank you.

[Photon939]

What earphone are you using?

A crystal radio is supposed to use a crystal earphone (piezo or similar?) they are very high impedance which is required to run from a crystal radio.

A regular 16 ohm magnetic voice coil headphone will probably just short out the crystal radio and result in no audio.

[t1d]

What earphone are you using?

A crystal radio is supposed to use a crystal earphone (piezo or similar?) they are very high impedance which is required to run from a crystal radio.

A regular 16 ohm magnetic voice coil headphone will probably just short out the crystal radio and result in no audio.

Thank you for your help. The earphone is of the proper type that you specify and it came from a Crystal Radio parts supplier. It is very sensitive and hurt my ear on testing.

[alanb]

A few things to check:-
1- Are your local stations AM
2- Is the resonant frequency of your circuit in their range use formula f= 1 /(2pi sqroot(LC))
3 - the loading of the earphone and parallel cap may be too great for the circuit. Are you using high impendence earphones? Reduce or remove C1

Good luck.

[alanb]

I notice that you say your antenna is still on the spool. You should unwind it and get it outside.

[Photon939]

What earphone are you using?

A crystal radio is supposed to use a crystal earphone (piezo or similar?) they are very high impedance which is required to run from a crystal radio.

A regular 16 ohm magnetic voice coil headphone will probably just short out the crystal radio and result in no audio.

Thank you for your help. The earphone is of the proper type that you specify and it came from a Crystal Radio parts supplier. It is very sensitive and hurt my ear on testing.

You mentioned the antenna was still coiled up on a spool? Try unwinding some antenna length and move it around, preferably high up to gather radio waves better than sitting on a spool.

I made a crystal radio years ago on those Radioshack xxx-in-one project sets and although it was not very selective between stations it did work and produced a fairly audible signal with just some scrap wire as an antenna and a wire connected to a copper water pipe as a ground.

[t1d]

A few things to check:-
1- Are your local stations AM
2- Is the resonant frequency of your circuit in their range use formula f= 1 /(2pi sqroot(LC))
3 - the loading of the earphone and parallel cap may be too great for the circuit. Are you using high impendence earphones? Reduce or remove C1

Good luck.

Thank you for replying. Yes, there are local AM stations.
No, I haven't done the math, but I would think that I would hear some sort of background noise, regardless.
The earphone was tested without the cap, with no improvement.

[t1d]

Thank you for the suggestions to unrole the antenna. I am aware that this is helpful, but YT instructionals indicated that the antenna may not even be needed, if the ground is sufficient and the stations are strong enough. Again, at this point, I am just looking for noise. I will properly mount the antenna, when the weather improves.

I take it that no one is seeing an error in the circuit design?

[Photon939]

The schematic looks ok, maybe try some other inductors? The one I built with the project kit looked similar to the ones found in commercial AM radios, a big ferrite bar antenna with multiple windings

[alanb]

No, I haven't done the math...

You can calculate the frequency with this

http://www.calctool.org/CALC/eng/electronics/RLC_circuit

[t1d]

Thanks guys!

[glarsson]

RF circuit built on a breadboard? Lots of extra C in the breadboard and extra L in the flying leads.

[metrologist]

I am trying to remember if I hear static noise on this simple crystal radio. I suspect normally not and the tuning is very sensitive, so it's easy to miss a station.

As said, you have to unwind the antenna and get it up in the air. The antenna is the only source of power so you will need a large aperture to capture enough energy to produce enough current in the circuit to get any sound.

Later I'll post some inductors that I built. I like open air wound inductors and in a basket weave. What kind of inductor are you using? BTW, an awesome way to integrate the inductor and antenna is to make the inductor the antenna in the form of a very large coil. I've seen some that are larger than a full grown man. I think mine is about 2 feet diameter and something like 16 turn primary and 3 to 5 turn secondary.

Below are some classic simple designs.

http://www.techlib.com/electronics/crystal.html

[t1d]

As said, you have to unwind the antenna and get it up in the air. The antenna is the only source of power so you will need a large aperture to capture enough energy to produce enough current in the circuit to get any sound.

Yep, will do.

Later I'll post some inductors that I built. I like open air wound inductors and in a basket weave. What kind of inductor are you using?

Just the little ones that look like common TH resistors. One of my ultimate design goals is to make a micro design, for minimalist camping.

BTW, an awesome way to integrate the inductor and antenna is to make the inductor the antenna in the form of a very large coil. I've seen some that are larger than a full grown man. I think mine is about 2 feet diameter and something like 16 turn primary and 3 to 5 turn secondary.

Cool...

Below are some classic simple designs.
http://www.techlib.com/electronics/crystal.html

Thanks!

[t1d]

You can calculate the frequency with this
http://www.calctool.org/CALC/eng/electronics/RLC_circuit

I looked at the link and I wasn't sure how to enter the information... What I would like to do is specify that:
- The channel is 710KHz, as it is AM.
- The resistance is 82K Ohms.
- The capacitance is midpoint of 0-335pF variable cap = 1/2 x 335pF = 167.5. Thereby, I can tune it, up or down.
Calculate the needed inductance, for the inductor.

I fooled around with the numbers and I may have hit it just about right... Using 82K Ohms, 167.5pF and just subbing in 300uH, the resonant frequency is 709.99KHz... That's nigh on perfect... Did I end up with the correct inductor value, or am I reading things incorrectly?

Thank you.

[GeoffreyF]

The antenna should be only one conductor and extended out, not touching the ground.   It should be mainly vertical, not horizontal. So attach the other end to a tree or whatever with a bit of string, not the wire itself.

The diode should be germanium, point contact type. If it was sold to you for this purpose then I assume it's fine. It's polarity does not matter in this.

I don't know what that resistor is for.  I would remove it.

If you are not close enough to a strong AM station, that could be the fundamental problem.  Tune the capacitor SLOWLY to see if you get anything.

[t1d]

The antenna should be only one conductor and extended out, not touching the ground.   It should be mainly vertical, not horizontal. So attach the other end to a tree or whatever with a bit of string, not the wire itself.

The diode should be germanium, point contact type. If it was sold to you for this purpose then I assume it's fine. It's polarity does not matter in this.

I don't know what that resistor is for.  I would remove it.

If you are not close enough to a strong AM station, that could be the fundamental problem.  Tune the capacitor SLOWLY to see if you get anything.

Thanks, Geoffrey... I will go vertical, outside, when the weather clears...

[t1d]

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...

[DJohn]

I would think that I would hear some sort of background noise, regardless.

It's been decades since I last played with a crystal radio, so I might be mistaken.  But I wouldn't expect to hear any noise if it's not tuned in to a station.  To get sound from the earpiece, something needs to provide it with energy.  There's not a lot of energy in background noise.  You can normally only hear it when it's amplified.

[PA0PBZ]

I don't know what that resistor is for.  I would remove it.

It's for discharging the capacitor so it can follow the modulation, otherwise the cap would charge and that's it. (depending on the earphone type used of course)

[vk6zgo]

As said, you have to unwind the antenna and get it up in the air. The antenna is the only source of power so you will need a large aperture to capture enough energy to produce enough current in the circuit to get any sound.

Yep, will do.

Later I'll post some inductors that I built. I like open air wound inductors and in a basket weave. What kind of inductor are you using?

Just the little ones that look like common TH resistors.

They are quite lossy, compared to a much larger inductor.
VK3YE has certainly used them successfully in some small receivers, but they all used active devices, where the losses are not quite as critical as in a Crystal set.

One of my ultimate design goals is to make a micro design, for minimalist camping.

BTW, an awesome way to integrate the inductor and antenna is to make the inductor the antenna in the form of a very large coil. I've seen some that are larger than a full grown man. I think mine is about 2 feet diameter and something like 16 turn primary and 3 to 5 turn secondary.

Cool...

Below are some classic simple designs.
http://www.techlib.com/electronics/crystal.html

Thanks!

[cdev]

This advice is not true, you need an antenna and ground, however, what I know from experience does work really really well is a loop antenna, several turns of wire in a big loop, a 365 pf capacitor should be able to resonate with a large enough loop, keep adding turns until you hear stations. You want to get your signals from a much smaller pickup loop inside the main loop, very loosely coupled.

With a good loop it will be generating several volts if you have strong local signals, enough to overload any receiver.

So the loops and the 365 pf cap are a separate resonant circuit inductively coupled to your pickup loop which replaces your current antenna. After that you should just need your germanium diode detector, your cap and your earphone, super simple.

I guarantee this will work if you give it a few turns of wire around hula hoop size to work with. You may even be able to receive some (the strongest) HF shortwave stations at night (using fewer turns.)

Thank you for the suggestions to unrole the antenna. I am aware that this is helpful, but YT instructionals indicated that the antenna may not even be needed, if the ground is sufficient and the stations are strong enough. Again, at this point, I am just looking for noise. I will properly mount the antenna, when the weather improves.

I take it that no one is seeing an error in the circuit design?

Don't use a thick PVC pipe for your coil, if you are using a coil wind it on something thinner. Very thin PVC pipe works, amber pill bottles work. Cardboard (from toilet paper) works. The higher the "Q" the better for selectivity.

[t1d]

This advice is not true, you need an antenna and ground, however, what I know from experience does work really really well is a loop antenna, several turns of wire in a big loop, a 365 pf capacitor should be able to resonate with a large enough loop, keep adding turns until you hear stations. You want to get your signals from a much smaller pickup loop inside the main loop, very loosely coupled.

Thanks for the tip. I am having trouble envisioning it. Could you post a sketch? Thanks.

[cdev]

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...

[metrologist]

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