# Tag Info

6

I don't know if this counts as "easy", but: Find the series resonant frequency. Multiply this frequency by $2\pi$ to convert it to an angular frequency, and call that $\omega_s$. Note the resistance at this frequency. That's $R$. Find the parallel resonant frequency, multiply by $2\pi$, and call it $\omega_p$. Halfway between these resonant ...

5

I'll try to address your concerns a bit! I'll be simplifying here and there, but I think you'll notice where I'm doing that. I'll be doing my best to explain to him how this works. I understand that when a radio ray passes over an antenna, it generates an alternating electrical field in the antenna wire. Close, but not quite :) I'll correct you here, ...

5

This design of a crystal radio relies on the capacitance of the antenna and the inter-winding capacitance of the inductor as well as the inductance of the inductor to form the tuned circuit. The length of the antenna can therefore play a role in the ability to tune in AM stations. I agree with Mike regarding the soldered connections. Go through them all ...

5

Sea water is not that conductive: about 5 S/m. By comparison, the conductivity of copper is about 60000000 S/m, so seven orders of magnitude more conductive. The low conductivity of sea water will effectively appear as a resistance in series with the coil. This will increase losses in the coil, reducing sensitivity. But worse, it will decrease the Q factor ...

4

I notice you have a BNC antenna socket, so I wonder if you're having the same problem I once had. I built a crystal radio kit, attached it to my HF antenna, and got essentially nothing. I then followed the kit instructions for a long-wire antenna connected directly to the terminals of the kit, and got much better results even though that antenna was strung ...

4

A crystal radio generally consists of a simple LC network and a diode detector. So in theory, altering the LC network would allow you to tune higher frequencies. The real issue is that signals you will find in the higher bands, simply do not have enough power to be detected without additional amplification. You have an even larger obstacle, however. A CW ...

3

Congratulations on a nice home-brew project! I started my journey into amateur radio with a crystal set such as yours. Making the inductor (coil) out of copper tubing is overkill from an electrical standpoint since very little current is involved. But you certainly gain significant mechanical strength and perhaps more importantly, aesthetic appeal from ...

3

I am no expert on House Wiring, but when mine was done, all the pipes in the house (central heating and water) were all grounded for safety reasons. I believe these were all connected to the main ground in the electrical cupboard where the meter is and the electrician checked to make sure it was a "good earth". So if you see the Green/Yellow wires attached ...

3

A bolt pushed into a pot full of dirt will never work! You need a ground return to planet earth itself for your crystal radio. :-) This could be as simple as the screw on a plastic cover that holds an electrical outlet in place. That's what I did when I was a kid. Also, some of those connections look "iffy". Make sure they are all making contact with an ...

1

I think if we were able to use perfect components, it would not matter. However, your antenna is not a perfect component. Is has many losses which result in a resistor R in its replacement diagram, in serial to C2. Now you can consider your antenna system as one resonant circuit consisting of: L/C of the wire, C2, L1, C1 and R. Looking at the circuit this ...

1

Really short answer, since I'm just passing by: What you state (narrow bandwidth for small capacitor) is not generally true, but low bandwidth means "there's a narrow peak of strong resonance* that's equivalent to "this is a very high-quality resonator" In a series RLC resonator with a fixed resistive component (whether that is really a resistor), the ...

1

A crystal radio is powered by the incoming signal. If you've ever listened to one, you'll know that the audio is quite faint, although a purpose-built transmitter could probably be made strong enough to overcome that problem. Traditional crystal radios receive AM only, and not in stereo. It could be theoretically possible to make a receiver powered by the ...

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