When I made my 4 foot X 4 foot tuned antenna, I used #14 wire which is a lot thicker than most people use in coils. I did discover, however, that I needed to go to a lower inductance and greater capacitance than than I thought was correct to get the biggest amplitude. Unloaded, it would make well over 1V on the scope. BTW: On a rocket radio I took apart, the slug's position was adjusted with a long thin brass threaded rod. The nose cone was glued onto the rod. To store it, you threaded the thing all the way in. To tune stations, you would thread the rod out. The treads worked on a metal cap on the end of the inductor's tube. If you are going for a small radio, that method may be better than a variable capacitor Even the ones they used in the early transistor radios would be about as large as the inductor part of the radio. You could make the coil on the outer housing of the radio and fit the capacitor within the inside of the coil as another option. Very conductive objects in a coil reduce the inductance without dropping the Q much.The plates can be arranged so that one dimension is along the major axis of the coil to reduce that effect.
@kensmith5694 Interesting information, thank you. I have been trying different coil / slug configurations, but can't get more than a 10 to 20 percent change in inductance. That's not nearly enough to tune in the AM band. Did your rocket radio have a small cap, like 3 pF?
@@tsbrownie Points at coil you can't see Points at slug you can't see 10.88mH without slug 61..55mH with slug Yes, it has a huge number of turns on it. Also, this is not enough range to do the whole dial. We need Range = 1700/500 = 3 is close enough F varies 1/sqrt(L) We need 3^2 = 10:1 close enough I may investigate further but a switch and a capacitor may be a good idea. ********************** Merry whatever you do to all who may pass this way
Got any of those old Christmas ornaments that were pointed on each end and had a center section that was long and tubular? We had them on our tree as a kid in blue, yellow and red and they had white christmas sceneries painted on the center sections. I guess someone could 3D print a simular shape. Wouldn't it be cool to wind a coil around the body of an ornament and convert it into a radio that you could hang on a Christmas tree?
Hi, do you know if it is okay to use coaxial cable with grounded shields to feed an antenna into the house? Would the shield interfere with the signal, for example, due to capacitance?
@Dark_Matter2 It has to do with impedence matching, and I don't know how to calculate / measure the input impedence of these crystal radios. You can always just give it a try.
@tsbrownie I can add 5 meters of coaxial cable between my antenna and radio, I can compare volume with and without that cable, with connected gound and without ground
I wouldn't have guessed the 2 coils would perform that way. Interesting results. It would be interesting to test where the self-resonant frequency is for the small coils and larger coil. your function generator and oscilloscope could test it. The further away from the medium band the better. Another curious thing is, do you get a a noticeable difference in reception if you orient your coils vertically? If your external antenna is doing most of the reception, the null-ing effect should be minimized. Also, could your external antenna being wound in a loop be creating a series inductance that is hurting the Q of circuit?
@aaronwoodard3354 I have tried standing the fine wire coil on end and did not notice any difference. I mentioned in another video that coiling up the antenna and ground wires like that can change the circuit. Usually, it's a slight decline, but every once in a while, it helps or at least makes no difference. I have the extra wire so I can move the radio to my other bench.
Maybe change the spacing between the turns of the coil. To lower the capacitance between the turns of the wire. It is only a idea, have no clue how this will change the performance.
It will drop the capacitance in the coil but I don't think it is a needed thing for the AM band. The tuning capacitor is huge compared to it. Scramble winding also decreases capacitance because there are gaps between the wires.
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cool. eager to see the developments!
When I made my 4 foot X 4 foot tuned antenna, I used #14 wire which is a lot thicker than most people use in coils. I did discover, however, that I needed to go to a lower inductance and greater capacitance than than I thought was correct to get the biggest amplitude. Unloaded, it would make well over 1V on the scope.
BTW: On a rocket radio I took apart, the slug's position was adjusted with a long thin brass threaded rod. The nose cone was glued onto the rod. To store it, you threaded the thing all the way in. To tune stations, you would thread the rod out. The treads worked on a metal cap on the end of the inductor's tube. If you are going for a small radio, that method may be better than a variable capacitor Even the ones they used in the early transistor radios would be about as large as the inductor part of the radio.
You could make the coil on the outer housing of the radio and fit the capacitor within the inside of the coil as another option. Very conductive objects in a coil reduce the inductance without dropping the Q much.The plates can be arranged so that one dimension is along the major axis of the coil to reduce that effect.
@kensmith5694 Interesting information, thank you. I have been trying different coil / slug configurations, but can't get more than a 10 to 20 percent change in inductance. That's not nearly enough to tune in the AM band. Did your rocket radio have a small cap, like 3 pF?
@@tsbrownie
Points at coil you can't see
Points at slug you can't see
10.88mH without slug
61..55mH with slug
Yes, it has a huge number of turns on it. Also, this is not enough range to do the whole dial. We need
Range = 1700/500 = 3 is close enough
F varies 1/sqrt(L)
We need 3^2 = 10:1 close enough
I may investigate further but a switch and a capacitor may be a good idea.
**********************
Merry whatever you do to all who may pass this way
@kensmith5694 Or multiple coils you can select.
Got any of those old Christmas ornaments that were pointed on each end and had a center section that was long and tubular?
We had them on our tree as a kid in blue, yellow and red and they had white christmas sceneries painted on the center sections.
I guess someone could 3D print a simular shape.
Wouldn't it be cool to wind a coil around the body of an ornament and convert it into a radio that you could hang on a Christmas tree?
Hi, do you know if it is okay to use coaxial cable with grounded shields to feed an antenna into the house? Would the shield interfere with the signal, for example, due to capacitance?
@Dark_Matter2 It has to do with impedence matching, and I don't know how to calculate / measure the input impedence of these crystal radios. You can always just give it a try.
@tsbrownie I can add 5 meters of coaxial cable between my antenna and radio, I can compare volume with and without that cable, with connected gound and without ground
@Dark_Matter2 That's a reasonable test.
I wouldn't have guessed the 2 coils would perform that way. Interesting results.
It would be interesting to test where the self-resonant frequency is for the small coils and larger coil. your function generator and oscilloscope could test it. The further away from the medium band the better. Another curious thing is, do you get a a noticeable difference in reception if you orient your coils vertically? If your external antenna is doing most of the reception, the null-ing effect should be minimized.
Also, could your external antenna being wound in a loop be creating a series inductance that is hurting the Q of circuit?
@aaronwoodard3354 I have tried standing the fine wire coil on end and did not notice any difference. I mentioned in another video that coiling up the antenna and ground wires like that can change the circuit. Usually, it's a slight decline, but every once in a while, it helps or at least makes no difference. I have the extra wire so I can move the radio to my other bench.
So the smaller one is 'scratchier'. The bigger more melodic. Anyone know why?
Maybe change the spacing between the turns of the coil. To lower the capacitance between the turns of the wire. It is only a idea, have no clue how this will change the performance.
Yes. That was my idea too. It should lower the capacitance but it is harder to make such a winding.
It will drop the capacitance in the coil but I don't think it is a needed thing for the AM band. The tuning capacitor is huge compared to it.
Scramble winding also decreases capacitance because there are gaps between the wires.
Like a bifilar "Mystery" set!
@@Pygar2 I also know that for making a coil with thick wire, using wire rope can work nearly as a well at litz wire.
@@kensmith5694 I have to wonder if putting a var. cap. between the antenna and bobbin would lower capacitance.
So, wait what?! You antenna is a spool of wire?!
@franzliszt3195 Sure, OR that's extra wire that leads outside to the antenna under the eaves of the house. ;)