Kids' "crystal radio", making an amplifier thereof

What you need is two crystal sets alongside each other, with one tuned to the most powerful station in the area, but instead of a speaker, you have big capacitors so you just rectify its signal and filter it to DC, then use that to power the set with the amp. ;-)

My first "crystal set" was a kit that came with a transistor, that detected and amplified, but it also used 2 D cells. My older brother had already built the simple one, which was really easy, since we were across the street from WCCO's 50 KW antenna. ;-) (well, about a half- mile away, actually.)

Cheers! Rich

some of those kits are absolute crap. does this one atleast function?

Not the skylab brand one is it? I encountered that one a few (~10) years back and had no luck with that one at all (I seem to recall it had no capacitor at all... could have the brand wrong too)

The cold water faucett business is alluding to needing a good earth connection but with plastic water pipes becoming increasingly popular I don't see that that's necessarily the best earth connection.

for good results from a crystal set a good earth connection and an long antenna wire are important.

you're going to need to isolate the audio section from the RF in the tuned circuit or otherwise provide a high impedance input or the thing is not going to work.

if your apliifier has low impedance (less than 100K) you probably benefit from a radio-freqency choke in series with the audio signal, if you've got a junk AM radio there one of those little square tin tunable transformers could probably be used for that purpose

easiest solution is powered speakers (like for mp3 player or pc)....

I'm not certain that they have enough sensitivity though, and they'll be low impedance input

see you in "sci.electronics.basics"

bye. Jasen

they work great at 100Mhz (for the FM band) but yeah absolutely useless at around 1Mhz for the AM band. silly store-person.

You disconnected it from the TV and used one side of the 300 ohm TV antenna lead to a roof mounted TV antenna as a long wire antenna. They were usually 50 feet or more and did work, but a longer wire was definitely better. Silly you.

We tried inner core, shield, or both together.

No combination worked.

It worked for me over 40 years ago.

Does the coax go through a ground block? If it does, it is shunting the RF to ground. I did it when 300 ohm twinlead was common.

I recall it was just co-ax cable.

My intuition at the time told me the inner was the aerial signal and the outer was the ground reference.

Years later I did feel it to be pretty lame.

While it might work under good circumstances (as it did for you), the father and son should not be disheartened if it does not. As an engineer I would recommend an aerial that was a decent fraction of the radio wave desired. IIRC, a quarter wave antenna is respectable. At 300 kHz a wavelength would be 299,792,458 / 300,000 = about 100 m, so a quarter wave would be 25m or about 75 feet.

If you are using coax for a TV antenna you would have to connect to the braid, because it blocks the signal from reaching the center conductor. There is a matching transformer at the antenna, or a matching stub, neither of which have good HF characteristics. Also, most of the coax is connected to the antenna frame for grounding which attenuates a lot of the HF signal.

The problem is, that the cable is parallel to the vertical mast, which is very probably grounded. So, they both get the same voltage induced in them, so there's no differential signal at the bottom end. Using the core doesn't work, because it's shielded.

But 300 ohm twin-lead doesn't have a rounded shield, and so one lead of it - or even both in parallel - make a dandy vertical random-wire antenna.

Cheers! Rich