Dx crystal radio!!!

[dime196604]

I saw a crystal radio kit at a thrift store for a dollar so i bought it, it was very basic. It came with a cardboard tube, enamel copper wire a diode and a 2000 ohm ear peace. Put it together with my four year old and it works, only picks up one station but it works. So i started searching the web for ways to improve it and make it tune-able. I found a massive amount of info, then i saw a Dx crystal radio. There are contests every year for dx crystal radios. So i kept on reading. There are some very complex designs for dx crystal radios that have a very wide tuning range. So now i am gonna try and make one. I don't have my hopes very high yet, as i keep reading that it takes many experiments of trial and error to get it down right, and like i said they are very very complex. I was just wondering if anyone else has read about, or tried to build one of these? It just amazes me at how well these can perform with no power except the radio waves.

[KP68]

I've experimented with them and it is pretty cool. They stem from Fox hole radios. WWI soldiers made these using anything available. For example, they got the wire from disabled vehicles and for the diode they used a razor blade, pin, and pencil led and of course, their crystal head sets.. To get different stations, one would have to make different tap points on the coil. Kind of strange that you brought this up. This evening I built one just to goof around a little bit. After I put stuff away, I logged on here and saw this post.

[KG4KGW]

Just some interesting history on the WWII foxhole radio.

These radios were not built by soldiers because they were easier to make or worked better than other radio designs of the day. The parts were readily available for much better radios and Europe was full of them in many of the houses and stores. Radio was the "TV" of the day.

The main reason they were built was because the German direction finding techniques were so advanced they could find an oscillator at great distances with little effort. The need for a receiver that didn't have a local oscillator brought about the foxhole radio.

If your going to use the razor blade don't forget to blue it or it won't work as well. Pencil lead makes a good diode too. There are a million designs for these on the net. The number of turns on your coil and the diameter of the wire will determine what frequencies you are on.

Vectronics makes a kit that is about $20 and I have used them to teach cub scouts about basic radio receivers. [Please login or register to view this link] They offer many kits from a simple foxhole radio on up to a full SSB transceiver. I have one of the 20 meter CW QRP radios that was built from a kit that I use when I go camping.

[dime196604]

The one i am planning one building is gonna have two main coils and one two gang vary-cap, and a single vary-cap, and a wave trap with a vary-cap also, and a diode, one ceramic cap, one resistor. The two main coils with have multiple taps, the wave trap is gonna be set up so you can rotate the coil 180* side to side. Also it will have a antenna tuner that you can switch in and out of the circuit. I am still trying to figure out how to wire a audio transformer inline so i don't have to use a 2000 ohm ear peace.

[KP68]

Hey dime, I thought the crystal ear piece was needed because of it being very sensitive to the minute electrical signals.

[KG4KGW]

Hey dime, I thought the crystal ear piece was needed because of it being very sensitive to the minute electrical signals.

They are very sensitive. If you were to put a matching transformer on it you would likely have to use some sort of amplifier to bring the levels up high enough for modern headphones. If you want a full size set of headphones you can always make a pair that is 2000 ohm.

[dime196604]

Hey dime, I thought the crystal ear piece was needed because of it being very sensitive to the minute electrical signals.

Yes you were right. I miss read, you gotta use the audio transformer for best performance when using a set of old navy sound powered phones. I thought it was for regular headphones. I am still in the learning process. I wanna build "The Lyonodyne" crystal set but it is very very complex, it was a contest winner for Dx crystal sets. I downloaded a few crystal radio books in pdf format and have been reading for a few days now

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Tue Nov 27, 2012 12:22 pm

Here is a schematic of the Lyonodyne


[Please login or register to view this link]

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Tue Nov 27, 2012 12:22 pm

Here is a schematic of the Lyonodyne


[Please login or register to view this link]

[KP68]

Man! I might have to get back into this stuff. I did a little searching last night and came across some pretty cool stuff. During some of my experimenting a while ago, I remember faintly hearing a St Louis baseball game (I'm in Pittsburgh) and a few other times I faintly heard some foreign language stations. I couldn't tell if some were transmissions from other countries or just ethnic radio stations relatively close by. Thanks for posting the schematics dime.

[dime196604]

Well I keep thinking I got the one I wanna build and then I find another I like better. I have found thousands of designs it so hard to choose what one to build

[KG4KGW]

[Please login or register to view this link]

The above link is to a PDF only. It is not intended to be to any website or otherwise divert from any sponsor. It is merely an instruction manual for a Vectronics VEC121K Crystal Radio Kit.

Since it was topic friendly and I thought it may help those who were not already skilled in building crystal radio sets it seemed appropriate to make it available for everyone else to enjoy. If you are interested in one of these kits they may be available to purchase at one of the vendors. I searched through them, but did not find them on any of the websites listed as sponsors. Someone with better knowledge of the sponsors inventory may be better able to answer that question.

Elevated Wire does not sell anything and there is nothing listed for sale by anyone currently on the site. This file is 11.11MB PDF reduced size format and may take some slower connection users a long time to download.

Enjoy

[zygoma]

Interesting thread! And one that makes me hark back to my formative years. It was a few years after my first foray as a Novice that I discovered Lafayette Radio Electronics and their affordable, tiny glass 1N34 (or 1N60? Don't remember now) germanium diodes and tunable loopstick antenna coils. A fixed cap had to be chosen to get the half of the U.S. AM broadcast band that was preferred, but a teensy ceramic disc cap took the place of a (relatively) huge variable cap. As long as one's favorite station (or stations) were among the two or three strongest in that band segment, the loopstick allowed tuning between them. In my case, in high school in the late 60s in Noo Joisee, it was WOR (for Jean Shepherd K2ORS's nightly show) or "Seventy-seven, Double-you A B Ceee!" for Top 40, both of which were in nearby NYC.

BTW, I suppose it's already obvious to anyone looking at building these, but might bear mentioning that grabbing just any old silicon diode from the parts bin is going to take a huge increase in available signal to have enough to detect. Germanium diodes will be more reliable and will work better with lower signal levels, because of the lower junction voltage drop.

A partially rusted, blued "safety razor" blade can have enough semi-conducting areas to allow for a gently applied safety pin to serve as the point contact. So could a rusty steel shed roof, but it would make the design considerably less portable....

I've been amassing some EFJ and Hammarlund variable caps here as spares for the boatanchor fleet, and am going to try one or two of the designs mentioned in here. It ought to be fun, and will be a chance to fiddle with steerable vertical loop antennas, too, to null out other stuff on the band.

Has anyone had particular luck yet in building any of these for a particular band? I'm rebuilding an ancient Griefkit grid dip meter right now, which should be a big help with tuning all those passive circuits.

Oops, I'm wandering again.
73

[KP68]

I've never tried to use anything but the 1N34A Germanium. It does make sense because of the .3 volt drop or .3 volts before conducting vs silicone's .7 For the razor, one can use a propane or MAPP Gas torch for the bluing process. BTW, was the bluing process once done because it made the blade last longer?

[zygoma]

I've never tried to use anything but the 1N34A Germanium. It does make sense because of the .3 volt drop or .3 volts before conducting vs silicone's .7 For the razor, one can use a propane or MAPP Gas torch for the bluing process. BTW, was the bluing process once done because it made the blade last longer?

Yessir, kinda like a controlled rust. Same as the process done to firearms frames, barrels, and actions.
Way back, when I took my gunsmithing course in Alaska, we learned to do hot bath bluing for the projects we were rebuilding. I've frankly forgotten the chemicals, but I recall being at the instructor's homestead, and he'd hauled out several small tanks made of stainless steel in various sizes and shapes, some propane heat racks on which to rest them. He then proceeded to don a rubber apron, gloves, and boots, a large plastic head/face shield, and hauled out plastic jugs of liquids that were covered with an assortment of large red lettering and pirate flags (Yarrrgghhh!)
Some judicious pouring, stringing of our projects' parts on stainless wire leaders to keep them together, a murmured incantation, the sacrifice of a small lamb, and the ceremonial lighting of the propane jets (by the newest guy in the class; apparently the most expendable....) and then we all went, by a carefully chosen upwind path, into the house for some possibly deserved beer and a few hour wait.

A couple of the guys in the class had built muzzleloaders, and opted for plum brown finish rather than bluing, for period authenticity. I have no knowledge of the process for browning, but it obviously predated bluing.

These days most razor blades are made of stainless steel instead of blued steel. I don't know know if it's because the bluing process is so toxic, or because it's just become so economical to manufacture stainless in quantity and machine it easily that it's a better deal all around. It does seem to have an almost infinite shelf life, as opposed to blued steel. I don't even know if anyone sells blued steel razor blades anymore, but they'd be great to find even if just for the renewed interest in minimalist radios.

Wifey has threatened to buy me a book with a title similar to "Answering questions with fewer than ten words". I dunno if it exists, but I suspect she'll be first in line for the book signing if one shows up on the market

Toodles

[dime196604]

Ok got the one that i am gonna build, it from the boys book of crystal sets it is figure 25A. You can find free PDF downloads of this book all over the net. I don't know how to post PDF's here otherwise i would post the schematic of it.

[KP68]

Great find dime! Thanks for sharing. Man, there's a ton of designs in there. BTW, I found a cool PDF called 40 uses for Germanium Diodes by Sylvania Electric. So many cool circuits in it. I'll email it to you.

[dime196604]

Great find dime! Thanks for sharing. Man, there's a ton of designs in there. BTW, I found a cool PDF called 40 uses for Germanium Diodes by Sylvania Electric. So many cool circuits in it. I'll email it to you.

there is a lot of nice circuits in there.

[Slyguy]

boys_book_of_crystal_sets.pdf

Here you go Dime

[dime196604]

Thanks for the link sly.

Here is another website that's has hundreds of plans, and competition crystal radio. It has every thing from beginner sets to to very completed performance sets

crystalradio.net

[KP68]

Wowa! What an awesome site. One of the things that grabbed my attention was the tube section. I really liked the "one tube radio can be mailed" and "amplifier fits on headphone". I know some tubes are small, but I didn't think they made them that tiny. One of these days I would love to get an LCR meter (price,ouch!), but for now the section called "Professor Coyle Calculator" for cylinder and especially spyderweb coils comes in real handy. Thanks so much for turning me on to that site dime.