Crystal Radio Breadboard - Zero Sound - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: December 19, 2018, 04:20:06 pm
content: 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.

author: Photon939
author_rank: Regular Contributor
timestamp: December 19, 2018, 04:29:42 pm
content: 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.

author: t1d
author_rank: Super Contributor
timestamp: December 19, 2018, 04:33:13 pm
content: Quote from: Photon939 on December 19, 2018, 04:29:42 pmThank 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.

author: alanb
author_rank: Frequent Contributor
timestamp: December 19, 2018, 04:37:18 pm
content: A few things to check:-1- Are your local stations AM2- 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 C1Good luck.

author: alanb
author_rank: Frequent Contributor
timestamp: December 19, 2018, 04:42:56 pm
content: I notice that you say your antenna is still on the spool. You should unwind it and get it outside.

author: Photon939
author_rank: Regular Contributor
timestamp: December 19, 2018, 04:45:11 pm
content: Quote from: t1d on December 19, 2018, 04:33:13 pmYou 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.

author: t1d
author_rank: Super Contributor
timestamp: December 19, 2018, 04:50:49 pm
content: Quote from: alanb on December 19, 2018, 04:37:18 pmThank 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.

author: t1d
author_rank: Super Contributor
timestamp: December 19, 2018, 04:55:16 pm
content: 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?

author: Photon939
author_rank: Regular Contributor
timestamp: December 19, 2018, 05:08:06 pm
content: 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

author: alanb
author_rank: Frequent Contributor
timestamp: December 19, 2018, 05:16:11 pm
content: Quote from: t1d on December 19, 2018, 04:50:49 pmYou can calculate the frequency with thishttp://www.calctool.org/CALC/eng/electronics/RLC_circuit

author: t1d
author_rank: Super Contributor
timestamp: December 19, 2018, 05:56:34 pm
content: Thanks guys!

author: glarsson
author_rank: Frequent Contributor
timestamp: December 19, 2018, 06:09:17 pm
content: RF circuit built on a breadboard? Lots of extra C in the breadboard and extra L in the flying leads.

author: metrologist
author_rank: Super Contributor
timestamp: December 19, 2018, 06:29:34 pm
content: 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

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 02:14:00 am
content: Quote from: metrologist on December 19, 2018, 06:29:34 pmYep, will do.Quote from: metrologist on December 19, 2018, 06:29:34 pmJust the little ones that look like common TH resistors. One of my ultimate design goals is to make a micro design, for minimalist camping.Quote from: metrologist on December 19, 2018, 06:29:34 pmCool...Quote from: metrologist on December 19, 2018, 06:29:34 pmThanks!

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 02:38:55 am
content: Quote from: alanb on December 19, 2018, 05:16:11 pmI 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.

author: GeoffreyF
author_rank: Regular Contributor
timestamp: December 20, 2018, 02:50:32 am
content: 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.

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 03:19:24 am
content: Quote from: GeoffreyF on December 20, 2018, 02:50:32 amThanks, Geoffrey... I will go vertical, outside, when the weather clears...

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 03:44:26 am
content: 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...

author: DJohn
author_rank: Regular Contributor
timestamp: December 20, 2018, 01:49:37 pm
content: Quote from: t1d on December 19, 2018, 04:50:49 pmIt'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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 20, 2018, 02:09:32 pm
content: Quote from: GeoffreyF on December 20, 2018, 02:50:32 amIt'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)

author: vk6zgo
author_rank: Super Contributor
timestamp: December 20, 2018, 02:25:26 pm
content: Quote from: t1d on December 20, 2018, 02:14:00 amThey 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.Quote

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 02:54:32 pm
content: 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 generatingseveral voltsif 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.)Quote from: t1d on December 19, 2018, 04:55:16 pmDon'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.

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 03:06:48 pm
content: Quote from: cdev on December 20, 2018, 02:54:32 pmThanks for the tip. I am having trouble envisioning it. Could you post a sketch? Thanks.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 03:08:46 pm
content: 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.Quote from: t1d on December 20, 2018, 03:44:26 am

author: metrologist
author_rank: Super Contributor
timestamp: December 20, 2018, 03:39:06 pm
content: 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

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 07:04:48 pm
content: Quote from: cdev on December 20, 2018, 03:08:46 pmThanks for this. I think I am catching on. It should be fun to try...

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 07:06:45 pm
content: Quote from: metrologist on December 20, 2018, 03:39:06 pmGood information... Thank you for your efforts to post the pictures. Cool design...

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 07:11:54 pm
content: Shortwave signals may only be audible at night, but they will fill the bands at higher frequencies than AM (fewer turns required)

author: t1d
author_rank: Super Contributor
timestamp: December 20, 2018, 07:17:48 pm
content: Quote from: cdev on December 20, 2018, 07:11:54 pmShortwave? Excellent.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 07:22:39 pm
content: 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.

author: chris_leyson
author_rank: Super Contributor
timestamp: December 20, 2018, 08:45:23 pm
content: 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.

author: StillTrying
author_rank: Super Contributor
timestamp: December 20, 2018, 10:06:32 pm
content: 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.

author: metrologist
author_rank: Super Contributor
timestamp: December 21, 2018, 12:56:49 am
content: Quote from: StillTrying on December 20, 2018, 10:06:32 pmHow do you ping?

author: t1d
author_rank: Super Contributor
timestamp: December 21, 2018, 01:52:41 am
content: 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

author: vk6zgo
author_rank: Super Contributor
timestamp: December 21, 2018, 03:15:25 am
content: Quote from: t1d on December 21, 2018, 01:52:41 amDo 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

author: spec
author_rank: Frequent Contributor
timestamp: December 21, 2018, 04:01:10 am
content: Hi t1dCheck 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.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2018, 06:03:03 am
content: 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.

author: mikerj
author_rank: Super Contributor
timestamp: December 21, 2018, 11:03:23 am
content: Quote from: chris_leyson on December 20, 2018, 08:45:23 pmPretty 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.

author: StillTrying
author_rank: Super Contributor
timestamp: December 21, 2018, 12:35:38 pm
content: Quote from: metrologist on December 21, 2018, 12:56:49 amFlick 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.yellowThe recommended 1n + 82k gives a much better output.blue

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2018, 04:28:33 pm
content: Quote from: cdev on December 20, 2018, 07:11:54 pmI thought that short wave is mostly single side band, which can't be picked up with a diode detector?

author: metrologist
author_rank: Super Contributor
timestamp: December 21, 2018, 07:03:56 pm
content: I think AM is more common for commercial shortwave broadcast. Voice comms typically use SSB.

author: iMo
author_rank: Super Contributor
timestamp: December 21, 2018, 08:19:03 pm
content: 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

author: chris_leyson
author_rank: Super Contributor
timestamp: December 21, 2018, 08:53:01 pm
content: Link to a kist of SW broadcast bandshttps://www.short-wave.info/index.php?feature=frequenciesPicked 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.

author: cdev
author_rank: Super Contributor
timestamp: December 23, 2018, 06:57:31 pm
content: 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.