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| Crystal Radio Breadboard - Zero Sound |
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| vk6zgo:
--- Quote from: t1d on December 20, 2018, 02:14:00 am --- --- Quote from: metrologist on December 19, 2018, 06:29:34 pm ---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. --- End quote --- Yep, will do. --- Quote from: metrologist on December 19, 2018, 06:29:34 pm ---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? --- End quote --- Just the little ones that look like common TH resistors. --- End quote --- 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. --- Quote ---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 pm --- 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. --- End quote --- Cool... --- Quote from: metrologist on December 19, 2018, 06:29:34 pm ---Below are some classic simple designs. http://www.techlib.com/electronics/crystal.html --- End quote --- Thanks! --- End quote --- |
| 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.) --- Quote from: t1d on December 19, 2018, 04:55:16 pm ---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? --- End quote --- 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:
--- Quote from: cdev on December 20, 2018, 02:54:32 pm ---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. --- End quote --- 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. --- 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... --- End quote --- |
| 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 |
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