Posted on 11/02/2010 10:48:58 AM PDT by djf
Is it kosher for a Jew to operate a ham radio?
Well, I may have been exaggerating just a little. 20 amps would probably be a sort of "high-side" estimate.
Project bookmark.
Another great brand of antique headphones was Brandes and they are common to find. In my experience, the old phones produce much better fidelity and louder sound on strong local stations, but are not as sensitive to faint stations as the cheapo piezo earpieces. When I had better hearing, I could pull in stations hundreds of miles away. In fact, I had a crystal set tuned to the low end of the shortwave band and heard stations in Europe.
The name of the game is experimentation. The single coil sets tend to be louder, but tune poorly. Multi-coil sets tune better, but often are not as loud. Try different lengths of antennas, mounted high and low. Drive a copper rod into the ground as far as you can and then water the ground around it until the ground is really soaked.
When I was a kid, my dad ran wire all the way around the house under the eaves for my antenna. I would say you need a better antenna or get it up high.
:+|
You should probably be using a germanium rather than a silicon diode (e.g. 1N34)
The kit calls it a Shottky diode. Not sure if that’s germanium or silicon.
I agree with others who suggest a good ground. In modern houses, the cold water pipe does not usually go to ground. Instead, look right under your electric meter or gas meter outside. There should be a ground rod there you can connect on to.
Why is ground important at these low frequencies? Because your wire antenna, as long as it is, is really only half an antenna. The other half is made up by ground. The wavelength is really long on the AM band (>160 meters).
“Unless you’re in a city, the best time for listening is after sundown. AM wave propagation gets better as the night wears on.”
AM stations now have to reduce power from sunset to sunrise. AM radio becomes a ghost town after sunset, even in the city many stations become unlistenable.
They’re silicon, but have very low forward voltage drop (generally better than germanium and much better than standard silicon diodes). That should be fine for a crystal set.
Crystal Set Society:
http://www.midnightscience.com/
That's silicon. It is difficult to construct a reliable Schottky diode (metal-semiconductor junction) on germanium, because metal vapor deposition doesn't work that well on Ge. Anyway, a good Schottky is almost a good a choice as germanium, because the forward voltages are both under 0.5 volts. I've measured silicon Schottky diodes at under 0.4V at low currents like you're likely to experience in your crystal radio.
Thanks! Good links.
I’m very interested in the formulas and calculations. Trying to calculate the inductance, capacitance, etc.
Seeing what happens if I add more coils. Different insulating materials on the capacitor. That sort of thing.
Self-ping for later
I’m going to be putting in a ground for a shortwave dx antenna in the next couple of weeks. Is it necessary that the wire between the antenna ground terminal and the actual ground is extremely low impedence/resistance? What type of wire would you suggest for a 15-ft run to a ground rod?
Dittos.
On the ground, preferably make a good connection to a ground rod driven into the earth. Sometimes wall socket grounds aren't all they should be, and with plastic pipes tthe water pipe isn't so great either.
You can buy the ground rod at a hardware store.
The idea of the coil and capacitor is to create a resonant circut. Changing the coil (more turns) will change the frequency away from the AM band.
The added ground is a much better idea.
“What type of wire would you suggest for a 15-ft run to a ground rod?”
For SW DX it is not critical at all. Multi-strand wire like a lamp cord or speaker wire or a single-strand solid copper wire will work fine. Just make sure both the wire and rod are clean and bright metal when you make a connection. You could use a clamp to fasten them together or even solder the wire to the rod.
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