two quick questions - Page 1
Forum section: electronics / beginners

author: josephpate
author_rank: Contributor
timestamp: December 08, 2012, 05:06:18 pm
content: 1) I got my hands on some oscillator crystals and I wanted to look at them on my scope. Does anyone have a VERY simple circuit I can breadboard up just to get any sort of waveform out of it?2) Anyone have a link to a crystal radio circuit using off the shelf parts? all of the tutorials I find online use hand wound inductors and aluminum foil home made capacitors.I found a calculator that i can use to determine the values i need for inductor/ variable capicitor but since i've never shopped for those before I dont really know what i'm looking for. Actual circuit schematic with part numbers would be a huge help!Thanks in advance.

author: DonRon
author_rank: Regular Contributor
timestamp: December 08, 2012, 05:24:44 pm
content: Hi Jo...have a look at this very interesting webpagehttp://www.qrp.pops.net/crystal-tester-2010.aspThere u will find a lot of rf-stuff - also this documenthttp://pages.suddenlink.net/wa5bdu/crystal_slide_show.pdfconcerning the crystal parameter checker. on page 15 there is a schematics of an oscillator to check crystals.Cheers,Ronald

author: josephpate
author_rank: Contributor
timestamp: December 08, 2012, 07:38:11 pm
content: Hmm looks relatively simple. Would different npn transistors work? I'm not sure which ones I have in my box.

author: c4757p
author_rank: Super Contributor
timestamp: December 08, 2012, 09:10:06 pm
content: You don't have 2N3904? It's a pretty basic transistor, you should be able to use just about anything.

author: josephpate
author_rank: Contributor
timestamp: December 09, 2012, 12:12:40 am
content: I was at work so couldn't check.The 2 types I found without digging through boxes were BC549CTA and BC547CBU (fairchild semiconductor it says)As I recall those were the cheapest ones i could find on mouser at the time.I will work up the circuit and let you guys know if it works.In the mean time, any sugestions on the crystal radio?

author: IanB
author_rank: Super Contributor
timestamp: December 09, 2012, 01:24:01 am
content: Quote from: josephpate on December 08, 2012, 05:06:18 pmEvery crystal radio tutorial for the past 100 years has involved hand wound coils and other home-made parts. In fact, if you go anywhere near ham radio you will discover that winding your own coils is universally considered to be part of the art. What objection do you have to this?Variable capacitors are possibly more likely to be specified as an off the shelf part, though I believe they are somewhat rarer and harder to obtain than they might have been a few decades ago. One possible source is old radios from yard sales and goodwill stores. Re-use and recycle, give life to old things.But overall, why are you so unwilling to undertake the essence of crystal radio construction, which is to make a working radio without buying or using any off the shelf parts? The perfect crystal radio will not use any purchased parts at all (except maybe the earpiece).

author: josephpate
author_rank: Contributor
timestamp: December 09, 2012, 03:40:45 am
content: Mainly didnt want the thing to be huge.Also I've never really considered tradition to be a good enough reason to do something.

author: c4757p
author_rank: Super Contributor
timestamp: December 09, 2012, 04:05:00 am
content: Quote from: josephpate on December 09, 2012, 03:40:45 amIt seems kind of pointless in my opinion to build a crystal radio that way, though. It is A) a circuit that can be built very easily with homemade parts, and B) shitty. If you're using off-the-shelf parts why not build a better radio? It's not like you're really learning anything about it by throwing together off-the-shelf parts, so why bother? The main point of extremely simplified circuits like that is to learn about them as you build them.

author: josephpate
author_rank: Contributor
timestamp: December 09, 2012, 06:34:40 pm
content: Fine, do you have any circuits I can build to make a better-that-crystal radio?Doesnt have to be a crystal radio in particular, just figured that would be easiest.

author: c4757p
author_rank: Super Contributor
timestamp: December 09, 2012, 06:48:10 pm
content: They're all over the Internet. I just went to Google and searched for "radio receiver circuits" and got pages of them, some FM. But unless you take the time to learn about them, you'll have no clue what to do when it doesn't work - and youwillhave that problem. Radio circuits are finicky.And all of them call for hand-wound inductors too.

author: josephpate
author_rank: Contributor
timestamp: December 09, 2012, 07:34:56 pm
content: I'll look those up, thanks.QuoteI've read about the basic theory behind crystal radios, but do you have some other way for me to "learn about them" without building it up and getting it working?I'm a beginner at all of this, but most of the advice i've found on the internet is to try to build things, fail, debug them and you'll learn that way. that's what I was trying to do here -_- I wanted to make a simple radio using parts that would be used in an actual radio (not hand wound inductors and aluminum foil toilet paper tubes), then connect it to the headphone amplifier I made.

author: c4757p
author_rank: Super Contributor
timestamp: December 09, 2012, 07:44:51 pm
content: Hand-wound inductors are pretty common. I just stripped down a broken portable CRT television (circa 2003) for parts and the RF sections were stuffed with what look like small hand-wound (five to fifteen turns) inductors.Building it up and getting it workingishow to learn. I just think that if you start with a circuit simple enough to actually do that (crystal radio circuits are very simple), you should hand-make the parts that are usually hand made because that is an important part of the circuit. You need to be able to get it going properly even if the inductance of that hand-wound inductor isn't exactly spot-on, for instance, and so on. Inductive parts are so commonly made by hand that it's good to develop an intuition for them.If you're using parts that would be used in an "actual" radio, it's going to be a very hands-off design because they're all ICs now. The older pre-IC ones are packed with parts that are hard to find now, like trimmer inductors and so on, and tend to use more complicated designs to get better characteristics for the end user. Not a good starting point.

author: cwalex
author_rank: Frequent Contributor
timestamp: December 10, 2012, 12:27:22 am
content: You could just buy a kit if you don't want to make the parts. Jaycar sell one, I'm sure you can buy one just about anywhere.http://www.jaycar.com.au/productView.asp?ID=KV3540