Electronics > Beginners
Crystal Radio Breadboard - Zero Sound
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metrologist:
I think AM is more common for commercial shortwave broadcast. Voice comms typically use SSB.
iMo:
99% of the short wave AM broadcast stations were switched off already..
The crystal radios were popular many decades back (1920-1990) in times the strong local stations existed...
As a child I took a Ge diode, old 4kohm headphones, a few meters of wire and got a perfect loud signal. Added a transistor, 4k/4ohm transformer and a speaker and I was pretty happy.
The trick was the 50-500kW AM sw broadcast stations were "on 24x7" and almost everywhere across Europe (almost every larger town had its own, mine 100kW one at ~1300kHz was about 10km off my home).
Today you have to watch the exact 1-2hours long broadcast schedule of the few stations of interest left, and use a quality sw radio with a decent antenna :)
chris_leyson:
Link to a kist of SW broadcast bands https://www.short-wave.info/index.php?feature=frequencies
Picked up Radio Romania International on the 49m band whilst playing with an EMC test receiver the other day, also found an asian station, might have been Chinese, on 31m coming in at 100dBuV, that's 100mV at the 50\$\Omega\$ input with only 6' unmatched wire antenna. Test receiver has developed another fault however but the SW broadcast bands are still quite active.
cdev:
The cheapest shortwave radio that can be bought today is an RTLSDR blog version 3 USB dongle set to direct sampling mode. They are multiple generations of community refined improvements.  It has to be used with a computer but will offer endless radio-related entertainment. they cost around $25 and will still require your learning a fair amount of stuff and installing drivers to use it. Once you figure out how to use it you can find COTS dongles for under $10 and build them into circuits yourself. For HF pins 4+5 - the unused Q input on the RTL chip are a differential input which is very sensitive to HF, but you need an antialiasing (low pass) filter and ESD protection. Also soldering to the pins is difficult, but if you dont care about VHF you can use the 1+2 I input and solder to capacitors instead. Much easier.

That will be much better than a crystal radio. You could use a loop antenna if you built one for this project, that would work really great, plus be kind of visual, so much easier to tune.

A very high tech improvement on the crystal radio.
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