Troubleshooting Crystal Radio: Tips for Building and Improving Reception

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In summary: Can you describe your antenna and ground connection, please?Is there any capacitors in your circuit? A tuning capacitor and a smoothing capacitor after the diode detector, perhaps? Ideally, can you provide a circuit diagram of your crystal radio or an online pointer to the design you are using?Is your high impedance earpiece a piezo-electric (crystal) earpiece?Thank you for your help. I have attached a photo of the components.In summary, Mark is trying to build a crystal radio but it doesn't work. He doesn't have any experience with this type of project, so he is asking for help from the community. His antenna and ground connection are
  • #1
Mark Palmer
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2
If anybody here has any experience with building a crystal radio, I would appreciate a response.

My grandson and I are doing radio projects. This involves basic crystal build using a coil, diode, and resistor. The system is grounded and uses an antenna with no external power and a high impedance earpiece for audio.

The radio works for a few seconds when left hooked to the ground and antenna, but then the sound fades.

Any ideas?
 
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  • #2
Mark, welcome to PF.

Can you describe your antenna and ground connection, please?

Are there any capacitors in your circuit? A tuning capacitor and a smoothing capacitor after the diode detector, perhaps? Ideally, can you provide a circuit diagram of your crystal radio or an online pointer to the design you are using?

Is your high impedance earpiece a piezo-electric (crystal) earpiece?
 
  • #3
GrahamN-UK said:
Mark, welcome to PF.

Can you describe your antenna and ground connection, please?

Are there any capacitors in your circuit? A tuning capacitor and a smoothing capacitor after the diode detector, perhaps? Ideally, can you provide a circuit diagram of your crystal radio or an online pointer to the design you are using?

Is your high impedance earpiece a piezo-electric (crystal) earpiece?

Thanks for the response. I am on the periphery of my technical expertise...trying to get my grandson interested in something other than video games. We built one of these very in very similar fashion and it worked (sort of). I'm trying to improve the design. In answer:

I have attached a photo. There are no capacitors. The earpiece is a high impedance unit, Philmore No. 748, sold to be used with the crystal set. I have a verified ground connection, 50' of lamp wire antenna, 47k Ohm resistor, and Germanium diode.

VHJ4zcS.jpg
 

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  • #4
You have a resistor connected across the earpiece, which is good. You could check the resistor is making good contact. If you have a multimeter you can check for a resistance reading of about 47 kΩ between the earpiece screws. Try the multimeter leads round both ways as in one direction the diode and coil will short out the resistor and give a low reading. If you haven't got a multimeter just check the resistor leads are clean and are firmly gripped by the earpiece screws (but not so tightly that they pull the leads out of the resistor).

How did you verify the water pipe ground? Did you make your connection to the water pipe at a point where you can check there is continuous metal pipe between your connection and the ground? Metal water pipes can be joined to plastic pipes underground and hence offer poor Earth connections. Try pouring some water on the pipe where it enters the ground and see if that changes the behaviour. You could also try making your own Earth connection with a tent peg or by driving a couple of feet of copper water pipe (available from DIY stores) into some soil.
 
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  • #5
I built crystal radio kits as a child; so long ago that I cannot write down the circuits but one did have paper capacitors and tunable pizeo-electric crystal that could pick up AM radio stations and other signals. While grounding indoors on cold water pipes (hot water pipes did not work due to the water heater) picked up faint signals; a strong alligator clip on an external metal fence brought in clear signals. We sunk the steel fence posts ~12" (< 1/3 meter) in the ground connected with wire mesh fence.

The best rig had a solenoid type coil tuned by sliding an internal plunger IMS (if memory serves) not unlike your sliding rig. The solenoid arrangment made for a more compact unit and also reduced static (noise). The entire unpowered receiver fit in my shirt pocket. Replacing the small ground clip, the kind used for soldering, with a stronger clamp used to secure ground straps from a clothes drier, really improved reception. As did polishing oxide coating off critical connections as mentioned above.

Bravo for teaching children this technique. Crystal sets helped me understand electrical ground and electromagnetic radiation. The next project I helped my father build a vacuum tube powered HAM radio transmitter-receiver with Morse and voice, then re-built a black-and-white television receiver which I modified with "stereo" speakers and a photo-electric cell for remote on/off switching via a flashlight. Great fun.
 
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  • #6
This is mysterious, and thanks for the responses.

I am securely grounded to a cold water pipe. This is continuous copper, and I checked it by testing voltage to ground. I have a background in electrical work, but not in this area. I know that all my connections are secure, tested everything thoroughly.

I am learning this along with my grandson. We started off with this simple design, wish to expand to more advanced, but this one needs to work. Do you think I am OK with my antenna?
 
  • #7
Mark Palmer said:
The radio works for a few seconds when left hooked to the ground and antenna, but then the sound fades.
Mark Palmer said:
I have a verified ground connection, 50' of lamp wire antenna, 47k Ohm resistor, and Germanium diode.
Mark Palmer said:
Do you think I am OK with my antenna?
When you can hear a channel, can you tell what the call letters are so you can check the frequency? Is it in the AM band?

How have you run your antenna wire? Does it go up into a tall tree nearby? The more vertical it can be, the better it will work in the AM radio band (for the US).

How many spots on the crystal have you tried with the whisker point? Have you tried cleaning the crystal surface and letting it dry before trying probe points?

And I would think your house ground should work fine. Is your house electrical system well-grounded?
 
  • #8
Mark Palmer said:
This is mysterious, and thanks for the responses.

I am securely grounded to a cold water pipe. This is continuous copper, and I checked it by testing voltage to ground. I have a background in electrical work, but not in this area. I know that all my connections are secure, tested everything thoroughly.

I am learning this along with my grandson. We started off with this simple design, wish to expand to more advanced, but this one needs to work. Do you think I am OK with my antenna?

I'm sure you understand ground. As a child the concept was quite mysterious to me. Even as an adult radar tech, proper ground could be elusive. The soil in South-East Asia was so saturated with water at one site, we hammered in copper spikes ~45' (<15 meters) deep and still had ground problems particularly during wet monsoon season.

I seem to remember using a small coil of insulated wire that came with the crystal set as antenna. This was in a large valley in Northern California surrounded by radio transmitters on the hills and on Mount Hamilton, so reception was excellent. IMS we hooked the HAM radio via insulated antenna wire to a mod on the TV antenna. Reception was so good, I made a simple FM antenna by splitting a short section of the same wire into a "Y" tacked to an inner wall for a stereo receiver.

You could experiment with different antennas. I seem to remember using an extendible automobile AM antenna clipped to the crystal set a friend later gave me. These days there are probably Internet sites you can consult about reception in your area.
 
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  • #9
Mark Palmer said:
I am securely grounded to a cold water pipe. This is continuous copper, and I checked it by testing voltage to ground.
Do you think I am OK with my antenna?
...this one needs to work.

0 V to ground might just mean an open circuit rather than a good connection. Some plumbing connections, especially fast-fit ones, can act as insulators though this obviously won't be a problem with continuous copper pipe.

The 50' antenna wire sounds plausible. Whether it's adequate depends on how far away is your nearest radio station in the band the receiver is tuned for. Keep the antenna off the ground and reasonably straight. If you can't get it largely vertical, as suggested by berkeman, try swinging it round horizontally by up to 90° to see if you can pick up other stations.

When I've tried low-end crystal or similar radio designs I've found that tuning is limited to varying the strength of the nearest strong radio station rather than selecting between multiple stations as expected on a modern commercial radio. Whilst crystal sets can be great fun if you can get them working, radio conditions have moved on a long way since their hey-day so don't give up if you can't get good results. A kit or design with built-in amplification may be easier to get to work. The next step in radio design is a TRF (tuned radio frequency) design. This will have an amplifier which frees you from the requirement for a good antenna and Earth as well as having a reasonably local transmitter.
 
  • #10
Mark Palmer said:
have attached a photo. There are no capacitors. The earpiece is a high impedance unit, Philmore No. 748, sold to be used with the crystal set.

there should be a capacitor (variable) else you don't have a tuned circuit

a basic easiest circuit ...

n06cv.jpg
 

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  • #11
berkeman said:
How many spots on the crystal have you tried with the whisker point? Have you tried cleaning the crystal surface and letting it dry before trying probe points?

The photo caption shows a 1N84A germanium diode (partially hidden by the brass wiper) so these aren't issues.
 
  • #12
davenn said:
there should be a capacitor (variable) else you don't have a tuned circuit

The coil is tuned against the self-capacitance of both the coil and the antenna wire. This does make it rather hard to predict quite what the radio is tuned to (hence berkeman's question about what is being heard).
 
  • #13
GrahamN-UK said:
The photo caption shows a 1N84A germanium diode (partially hidden by the brass wiper) so these aren't issues.
Oh, shoot, I misunderstood. Thanks for clarifying that. I saw "crystal radio", and made assumptions that was what the project was. What's a more accurate thread title -- just a simple unpowered AM radio receiver?
 
  • #14
berkeman said:
I saw "crystal radio", and made assumptions that was what the project was. What's a more accurate thread title -- just a simple unpowered AM radio receiver?

'Crystal set' is still standard usage among ham and other hobby radio users for unpowered (strictly, signal-powered) radio designs even if they use commercial diodes as detectors so the thread title is fine.

If you're sufficiently hard-core you can still track down a cat's whisker and galena crystal to make your own diode detector:
https://en.wikipedia.org/wiki/Galena#Galena_uses

There are hobby groups for making high-performance crystal sets. The designs can be more complicated than building powered radio sets with amplification.
 
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  • #15
GrahamN-UK said:
The coil is tuned against the self-capacitance of both the coil and the antenna wire. This does make it rather hard to predict quite what the radio is tuned to (hence berkeman's question about what is being heard).
yeah, very hard
@Mark Palmer would be much better off using the more standard style of circuit I posted as it is going to give
better and more easily/predictably obtained results
 
  • #16
The fact that it works for a short time then fades shows it is at least tuned to a transmitter, the antenna (and likely Ground) is adequate, the crystal is functional, and the earpiece functions.

Since the earpiece is labeled as High Impedance, it is probably of piezoelectric construction (about the only type that works with a crystal radio!). Being piezoelectric, to the outside world the earpiece presents as a capacitor, which will charge up, acting as a filter cap, from the rectified receive signal. That is the purpose of the 47k resistor, to discharge the DC on the earpiece. Without the resistor, the earpiece charges to the peak voltage of the received signal and the diode (crystal) is biased off.

Possible causes:
  • Earpiece not connected correctly
  • Resistor faulty
  • Resistor not connected correctly
Conclusion: replace the resistor

Cheers,
Tom
 
  • #17
Thanks, all. I did not expect such assistance.This is nothing more than a simple AM unpowered receiver unit if there was any question on it.

I think the earpiece is OK. I ordered a couple of extras and the problem seems to be be present with all of them. I have checked all the connections and am satisfied they are correct. I have not been able to receive a signal strong and long enough to identify what is coming thru the set. I am not happy with the antenna, but I figured it would work well enough to get something consistent and it has not so far. As far as the ground is concerned, I tested it with AC voltage to make sure. I show a full 120 VAC going to ground on the cold water pipe I am using. The pipe is copper all the way to the street, buried to the main a distance of 50', about 48" deep.

I have some fundamental questions based on ignorance.

1. Does the use of schedule 40 pipe for the coil have any impact on the performance of the coil? Most of these are depicted using paper tubing or such.
2. If the earpiece acts as a capacitor as mentioned earlier in the thread, is it discharging to ground thru me to ground when I put it in my ear, thus causing loss of signal?
3. I am using 22 AWG wire on the coil. Is this OK?
4. I see different schematics for this type radio, some of which shown very specific number of winds on the coil. I just wound this coil until I ran out of room. What should work best?
5. The subject of the ground has been raised by a couple of people. If there was a ground issue, what symptom of this would be present?
6. I am using a single strand of insulated stranded lamp wire (maybe 18 gauge) for the antenna. Could this be a problem as to the type?

This is really interesting stuff, and I appreciate the feedback. My grandson is excited about the project. If we can get this one going I want to go on to a more advanced design.

Thanks again.

Mark Palmer
Louisville, KY
 
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  • #18
i can't quite make out the color code on your 47 KΩ resistor.

At 600% it looks like it could have a yellow multiplier and that'd be 470 K Ω
upload_2019-2-18_13-10-15.png


make sure it's yellow-violet-orange not yellow-violet-yellow.

my two cents, and overpriced at that..

i still remember my crystal radio - what fun. It'd only get Miami's clear channel station, WINZ , "fifty thousand watts of music and news"" was their jingle.

old jim
 

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  • #19
jim hardy said:
i can't quite make out the color code on your 47 KΩ resistor.

At 600% it looks like it could have a yellow multiplier and that'd be 470 K Ω
View attachment 238944

make sure it's yellow-violet-orange not yellow-violet-yellow.

my two cents, and overpriced at that..

i still remember my crystal radio - what fun. It'd only get Miami's clear channel station, WINZ , "fifty thousand watts of music and news"" was their jingle.

old jim
 
  • #20
It was sure bought and labeled 47k. Try this high res pic. I don't know the color bands.

DR6nHvM.jpg
 

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  • #21
Consider wrapping a/o soldering or otherwise securing the components. Wood screws into woodblock could loosen as you work the slider, etc.

(Mind you, thus from the worst solderer in the USAF. :cool:
 
  • #22
Klystron said:
Consider wrapping a/o soldering or otherwise securing the components. Wood screws into woodblock could loosen as you work the slider, etc.

(Mind you, thus from the worst solderer in the USAF. :cool:

I actually thought of that. I think the connections are secure. I have been over them. You can't tell from the photo, but the connections are caught between brass washers on the wire and components. The wiper bar connection is spring loaded.
 
  • #23
Mark Palmer said:
I actually thought of that. I think the connections are secure. I have been over them. You can't tell from the photo, but the connections are caught between brass washers on the wire and components. The wiper bar connection is spring loaded.
Yes, but brass is not a conductor. I have a set of brass tools for tuning sensitive circuits to avoid impedance changes from inserting tools. Not sure about the screws. Stores such as Fry's Electronics or other online sources sell inexpensive circuit boards with conducting wrap posts (apologies for my poor nomenclature) for DIY soldering projects.
 
  • #24
Klystron said:
Yes, but brass is not a conductor.

That could explain a lot. Let me look at this again.

Brass contains copper and it will read continuity. Is it insufficient for these small value transmissions?
 
  • #25
Allow me to defer to @jim hardy and other practical engineers.

(BTW, I like your avatar. "The Dude, abides.")
 
  • #26
Klystron said:
Yes, but brass is not a conductor

who-ever told you that ??
Yes it is it's a good conductor ... it's made from tin and copper, both good conductors, millions of RF connectors are made of brass
eg.
untitled.JPG
Klystron said:
I have a set of brass tools for tuning sensitive circuits to avoid impedance changes from inserting tools.

so my previous comment negates the reason for your use of brass as a tuning tool

It is used because it is non-ferrous/ferro-magnetic and that is why it has negliable effect on the tuningDave
 

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  • #27
Thanks for the clarification.
 
  • #28
Mark Palmer said:
Try this high res pic.
Much better, THANKS !

Looks like you're okay

upload_2019-2-18_15-33-10.png


i'm still unsure of the third band but you can look to make sure it's orange.

https://www.allaboutcircuits.com/textbook/reference/chpt-2/resistor-color-codes/

old jim
 

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  • #29
Mark Palmer said:
Thanks for the clarification.

Yes, Thanks for the correction. I'd like to say I confused "non-ferrous" with "non-conducting". While true for my brass tools, I had a fundamental misunderstanding.
davenn said:
who told you that [brass was a poor conductor]

I learned physics-chemistry-electronics at an early age from reading my father's old textbooks and tons of self-paced study. I must have misunderstood that adding tin to copper alters (conduction) characteristics. The old books may have been referring to thermal conduction; the really old books from my first college mainly discussed techniques to convert copper to brass to bronze for weapons. I always meant to study (modern) materials science but one cannot learn everything. Aside from some excellent material on wave mechanics sent by Dr. Dicke, I've had to re-learn almost everything taught in the Air Force after basic electronics (circa 1970). I'll shut up, now, but thanks for the knowledge.
 
  • #30
Isn't brass slightly diamagnetic ?
A natural enough psychic-cross-thread ...

old jim
 
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  • #31
Klystron said:
I must have misunderstood that adding tin to copper alters (conduction) characteristics.

yes it does and it is for the worst. Brass, isn't as good as copper.
Was also reading that the conductivity depends on the zinc content ... more zinc less conductivity, which is kinda interesting
 
  • #32
It's not easy to tell from your picture, but the wire on the coil looks as though the insulation is still present preventing the slider from making contact. Also the number of turns appears excessive. A coil with about 80 turns on a cardboard tube from a toilet paper or kitchen paper roll tuned with a 365 pF variable capacitor across it works fine for the AM band (531 - 1602 kHz), using a circuit like that posted by Davenn.
 
  • #33
Thanks again, all.

I am obviously new to this, and my "research" into the area comes up with a lot of variables. The conductivity of brass is interesting. The wiper bar I am using is brass, soldered to a brass ID tag which is spring loaded for tension. The question for me is whether I should be using something other than brass for the wiper bar. Most of the instructions I have seen just say to use wire hanger or bike spoke or such.

Also, I am still curious about the construct of the coil, to darth boozer's comment. I used schedule 40 pvc pipe, size 1.5" for the coil body, and I know I wound a bunch of wire on it. A couple of questions on the coil:

1. Does the heavy wall pvc pipe work any differently than a paper tube?
2. Does the excess winding degrade the radio tuning in some way?
3. I used fine grit sandpaper to clean the coating from the wire on the wiper path, brushing out the residue. Is this sufficient?

Thanks, all.
 
  • #34
I have another question on the diode. In reading up on diode technology, I see it is directional. Does this apply to the crystal radio? The right side of the coil is connected directly to the diode.

Pva43vH.jpg
 

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  • #35
Mark Palmer said:
1. Does the heavy wall pvc pipe work any differently than a paper tube?
i used PVC for my TV antenna. I googled and so far as i could tell it's electrically pretty near transparent.

I put a piece in the microwave for a minute and it didn't get warm to the touch
so i think it doesn't absorb significant RF energy.
 
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<h2>What is a crystal radio?</h2><p>A crystal radio is a simple radio receiver that uses a crystal diode as a detector to convert radio waves into audio signals. It requires no external power source and can pick up AM radio signals.</p><h2>Why is my crystal radio not working?</h2><p>There could be several reasons why your crystal radio is not working. Some common troubleshooting steps include checking the connections, making sure the antenna is properly positioned, and testing the crystal diode. It is also possible that there is no strong enough radio signal in your area for the crystal radio to pick up.</p><h2>How can I improve the reception of my crystal radio?</h2><p>To improve the reception of your crystal radio, you can try using a longer antenna or a better quality crystal diode. You can also experiment with different types of headphones or speakers to see which one produces better sound. Additionally, you can try adjusting the tuning coil to find the best frequency for the radio station you want to listen to.</p><h2>Can I use a crystal radio to pick up FM radio signals?</h2><p>No, a crystal radio is only capable of picking up AM radio signals. FM radio signals require a more complex receiver with a different type of detector.</p><h2>Is it possible to build a crystal radio without any soldering?</h2><p>Yes, it is possible to build a crystal radio without soldering. There are many crystal radio kits available that do not require soldering and can be easily assembled by following the instructions provided. However, if you are building a crystal radio from scratch, some soldering may be necessary to connect the components.</p>

What is a crystal radio?

A crystal radio is a simple radio receiver that uses a crystal diode as a detector to convert radio waves into audio signals. It requires no external power source and can pick up AM radio signals.

Why is my crystal radio not working?

There could be several reasons why your crystal radio is not working. Some common troubleshooting steps include checking the connections, making sure the antenna is properly positioned, and testing the crystal diode. It is also possible that there is no strong enough radio signal in your area for the crystal radio to pick up.

How can I improve the reception of my crystal radio?

To improve the reception of your crystal radio, you can try using a longer antenna or a better quality crystal diode. You can also experiment with different types of headphones or speakers to see which one produces better sound. Additionally, you can try adjusting the tuning coil to find the best frequency for the radio station you want to listen to.

Can I use a crystal radio to pick up FM radio signals?

No, a crystal radio is only capable of picking up AM radio signals. FM radio signals require a more complex receiver with a different type of detector.

Is it possible to build a crystal radio without any soldering?

Yes, it is possible to build a crystal radio without soldering. There are many crystal radio kits available that do not require soldering and can be easily assembled by following the instructions provided. However, if you are building a crystal radio from scratch, some soldering may be necessary to connect the components.

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