Getting Back into (Crystal) Radio sort of

[PA5COR]

The BAT 85 is 30 volt 0.2 Amp, 500 MHz
Look in the link i provided for the range of Schottky diodes and the replacements ;)

[kd8dey]

BAT85, ultra low noise Schottky diode.
I got a batch from Phillips for next to nothing.
Sharing them with the people here who desire to use them, so they find a good home where they will be actively used and not stay in a box here till i become S.K. ;)
Place your (free) order

Yep the guy knows his stuff ;) that';s why i put the link in.
http://www.rfmicrowave.it/catalogo/eng/A.pdf
Datasheet for the Schottky diodes for the technicaal buffs ;)
Use for detector diode, mixer diode, switching diode with low noise and low capacity in the ON state, ( replacing my switching diodes in the bandfilters in the FT 847's), replaces most diodes with germanium, generally lower voltage drop, lower noise.

Schottky diodes (also known as hot carrier diodes) are semiconductor diodes with a low forward voltage drop and a very fast switching action, the low forward voltage leading to increased efficiency. While standard silicon diodes have a forward voltage drop of about 0.6 volts, Schottky diodes voltage drop at forward biases of around 1 mA is in the range 0.15 V to 0.46 V, which makes them useful in voltage clamping applications and prevention of transistor saturation, due to the higher current density in the Schottky diode. Schottky diodes are suited for switch mode power supplies and high frequency DC to DC converters. This devices are intended for use in low voltage, high frequency inverters, free wheeling and polarity protection applications.

I figured that since I am using such a "Hot" Diode that it deserved a "decent" crystal radio wrapped around it :) .

So instead of the typical single tapped coil I want to do something a little more advanced. I'm planning on loosely coupling the antenna And perhaps the detector circuit BUT I am not finding any info on calculating the additional coils needed.

The actual tuning coil is no problem, standard math formula....now finding the info on the antenna or detector coupling coils is another story.

[PA5COR]

Most of the designs of the Dutch maker come with schematics including number of windings and diameter of the coil former.
Trial and error will bring you the optimum result, to many variables to give a detailed number.

Will have to pop off a few more to another member, will do it this week.
Soon we will have our own chrystal radio club ;)

[kd8dey]

Trial and error will bring you the optimum result, to many variables to give a detailed number.
Soon we will have our own chrystal radio club ;)

Kewel

looking around for info and parts etc I came across some good sites.

On "that other" site somebody posted a link for coil forms at
http://www.westernsierraradio.com/products.html
But they are a bit pricey especially for a 1 trick pony.

I found another establishment with comparable forms at a lot better price along with a lot more parts
http://peeblesoriginals.com/

So far these are some of the better sites I have found

Here is a site on Crystal DXing that I haven't had a chance to go through yet
http://homepage.ntlworld.com/lapthorn/xtal.htm

Also this place has been around for ages and has a newsletter
http://www.midnightscience.com/index.html

Another useful link
http://www.crystalradiosupply.com/index1.html

This one has quite a bit of info to browse
http://www.crystalradio.net/

[NQ6U]

On "that other" site somebody posted a link for coil forms at
http://www.westernsierraradio.com/products.html
But they are a bit pricey especially for a 1 trick pony.

Continuous grommets, sometimes called caterpillar grommets, are a good, cheap way to make air wound coils.

[KA5PIU]

Hello.

I was told that "this" would not work or "that" was better when building crystal radios.
It is just as bad as having an "elmer".
I built 5 crystal radios following plans I could find and based on what I could find for parts.
All worked just fine.
A few months later this dufus ham shows up and asks me for "his parts".
I aks him what parts and he says the there was a charge for his advice.
I pointed out that I took none of his advice and produced the drawings I did of the material I copied.
My very first experience of US hams.
The French ham I met who showed me woodworking helped me build all of the cabinets and forms needed.
I was called into the principals office, the gent argued that I had stolen from him.
I requested a complete and detailed explanation of what it was that I had stolen.
One week later I presented the 5 complete and working crystal radios, complete with spare parts I had fabricated.
It was clear that none of this was anything like what he brought, it was so much better!
Headphones? how about 5 pairs of rebuilt ones with modern omnimagnet diaphragms?
This is a very thin sheet of very magnetic alloy that produces a massive increase in volume over common sheet steel that is used.
You will find this in some horn speakers but can make your own easy enough.
And, speaking of speakers, I built a pair of them also. ;)
I later built a "phono ocillator" with one tube, a TV sweep tube!
Proper filtering was applied and so it ran clean, but there was zero chance it was within part 15 output specs!
This was a new tube I got cheap with the idea that I was to get my ticket soon.
There was a 4 transistor circuit driving this tube, all built inside the chassis of an old 5 tube AC/DC farm radio that was rebuilt for operation from AC from a TV transformer.
You could pull the back cover and everything looked normal, transistor circuits were under the chassis and the output tube was inside the battery box.
Turn it on and it worked like any radio, to transmit you would push the volume/power knob in.
I could carry it everywhere as it looked like any radio.
I got the idea from East Germany, where converting car radios to 2 way service must have been a national pastime. ;)

[PA5COR]

Carl
Your diodes are on ther way since this afternoon.
Hope the mailman is a bit fast ;)

Have fun with thm,

Cor

Continuous grommets, sometimes called caterpillar grommets, are a good, cheap way to make air wound coils.

[NQ6U]

Carl
Your diodes are on ther way since this afternoon.
Hope the mailman is a bit fast ;)

Have fun with thm,

Cor

Okay, Cor, thanks a bunch! I'm trying to get my ten-year-old grandson interested in radio (or, for that matter, anything other than himself) and I thought building up a working radio starting from a simple crystal set might be the way to do it.

[PA5COR]

Start with a simple Chrystal set, and show" see kid, no electricity and working fine" does open his eyes.
Use a decent length of antenna wire, and a good ground.

You can go from there to more sophisticated radio's adding amplification and selectivity and speaker.
But most kids turn on from seeing actually a radio work without electricity and listening to the earphone ( Hi Impedance) to the stations.

[kd8dey]

Grabbed a couple cheap plastic cutting boards from the local dollar store to make a couple spider coil forms.
planning on using 290uh for the inductance along with a 15-410pf capacitor from peebles if still in stock.

should give me plenty of leeway to cover the entire broadcast band.

The grandson's wrestling coach does woodwork. Since I don't have any hand-tools as far working dense plastic perhaps.... :)