Electronics > Beginners
Crystal Radio Breadboard - Zero Sound
t1d:
--- Quote from: cdev on December 20, 2018, 03:08:46 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.
--- Quote from: t1d on December 20, 2018, 03:44:26 am ---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...
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Thanks for this. I think I am catching on. It should be fun to try...
t1d:
--- Quote from: metrologist on December 20, 2018, 03:39:06 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
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Good information... Thank you for your efforts to post the pictures. Cool design...
cdev:
Shortwave signals may only be audible at night, but they will fill the bands at higher frequencies than AM (fewer turns required)
t1d:
--- Quote from: cdev 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)
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Shortwave? Excellent.
cdev:
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.
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