AM Radio Design Log

That's great. Perhaps the best way to start is to build a crystal radio. Once you get going with that, you can modify it with active devices and eventually drive a speaker.

I'm skipping the tubes, but I could recommend two books for you: Voice Of The Crystal and Instruments Of Amplification, which while written for electronics beginners are extremely neat because he builds his radios, tubes, and transistors from scratch using fairly common household items.

If someone is starting from scratch, a reaction set beats a lousy crystal massively. Crystal sets must be the worlds worst radios bar none.

NT

Actually that's what got me hooked on radio waves. I built a crystal set a few years back, and I am still trying to understand how it works (more on it in a future post). Thanks, I'll check out the books.

On Saturday, January 17, 2015 at 2:26:09 AM UTC-7, snipped-for-privacy@care2.com wrote:>

Never heard of a reaction set. Googling

To learn more about crystal radio, sign on to this forum.

Lots of fun there.

Mikek

Building a reaction set *entirely* from scratch would be much more difficult. There's a reason that the crystal radio is your basic first electronics / radio project.

Both are good projects though.

It is harder, though not by a lot, whats harder is using it. But the difference in result is huge. Crystals disappoint IME, reaction sets delight.

NT

What is a reaction set?

Don't know how to use search engines?

Google 'reaction set radio' answers your question in the 2nd link.

Jeroen Belleman

Okay, SmartAss...

This is the Google response where the second hit is...

Then it has a link to Reaction sets which are actually regenerative sets. But on that link there is nothing about reaction sets.

Do you know how to research properly?

Regenerative receiver. "Reaction sets, also known as regenerative receivers, rely on positive feedback to achieve adequate gain."

I hadn't heard of the term and had to Google for the clue.

Thanks, Jeff. Neither had I (obviously). Common usage would have prevented all this.

It's right there, I tell you: "Reaction sets, also known as regenerative receivers, rely on positive feedback to achieve adequate gain."

In modern parlance, they are resonant circuits with enough active feedback to set them on the verge of oscillation, so that a tiny bit of energy at the right frequency will be hugely amplified. They are very touchy and need constant tweaking.

Jeroen Belleman

For MW, long wave, and low shortwave broadcasts (7mHz), the ZN414/MK484 type TRF receivers are real easy to build, and work wondefully. They require besides a tuned circuit, a few extra passive components and a 1 volt battery. A 1 volt battery can be a 1.5 volt battery and more resistance, or a 1.5 volt battery used to the point it no longer can provide enough power for most things. It will last a year or more of continous use.

You can add some regeneration (or reactance) if you want for even more gain.

The latest version of the ZN414/MK484, the TA7642 works up to and including the 7mHz SW broadcast band, and costs about $6 for 100 on eBay.

If you do want to do a crystal radio, Soviet made D9b (often written wrongly as D95 (because the lower case Russian b looks like a 5) can be bought for $.10 each on eBay. If you avoid the fake germanium diodes, and only buy new old stock, you can get some interesting ones, such as the gold contact OA47 (UK) diodes, for about a UKP, and lots of current production Shottkey diodes sold for use in crystal radios.

Geoff.