Crystal Radio--Ferrite Coil Model #2 (4K)

[@tsbrownie]

I realized I was not clear with the wire sizes. The original ferrite was wrapped with 32 AWG (0.2mm) == 195 uH, the blue air coil was wrapped with 20 AWG (0.8 mm) == 205 uH. The second ferrite was wrapped with 24 AWG (0.55 mm) == 205 uH. Why did I change to 24 AWG? Turns out the 20 AWG wire is too wide and would not fit on the core.

[@junkmail4613]

75-year-old retired double E. I enjoyed your video. I also built a crystal radio back in 1963 with similar components. I was 20 mi from New York City, so WABC (50 kilowatts) could be received with only a headphone and a diode. Many memories thank you very much. Ten little indians (below) reminded me of 60 foot high tree I'd never have climbed 150 feet away from my house, to string an extremely powerful antenna to my bedroom window. It was great for a kid with no money to listen to night time radio on the sly. With no lightning arrestor, my Dear-ol'-Dad would have had a cardiac had he known. Kids are so crazy!!! I loved him.

[@tsbrownie]

Thanks for sharing. I did the diode radio thing as a kid too. It was like magic. I repeated it recently. (Diode Radio) World's Simplest Radio kzbin.info/www/bejne/o52ll3R_lJpog80

[@paulromsky9527]

At 11:08 ferrite core coils work better for Heterodyne radios. That is where a dual ganged capacitor is used. One capacitor tunes the coil (just like a crystal radio), the other capactor tunes a Local Oscillator (LO) so that the mix of the two produce the radio station tuned frequency, the Local Oscillator frequency, the sum of the frequencies, and the difference of the two frequencies. Only the difference is used (using a 465KHz low pass filter). The Local Oscillator mixes and results in 455KHz (in AM radios) no matter what station frequency is tuned. That 455KHz is known as the Itermediate Frequency (IF) and is Amplitude Modulated with the exact same signal as on the station signal (the modulation does not change frequency). Using this method down converts ANY tuned radio station frequency to this one IF. Now varoius stages (quite often 3) of band pass filters and amplifers are used to amplify only the IF signal +/- 10KHz (the bandwidth of the station signal), this cuts off all other stations to either side of tuned station, leaving only the strong tuned station. This is where very high station selectivity is achieved. The signal then goes through a Germainum Diode to cut off the negative levels of the IF signal, then the signal goes through a 20KHz Low Pass Filter (leaving the human range of audio signal only). Finally that signal is greatly amplified to drive a speaker with volume control. It's simple but requires many transistors, IF transformers, and DC power. Heterodyne was first done using vacuum tubes before transistors were invented.

[@t1d100]

I am so pleased that you 1) repurposed the board and 2) continued your investigation of the ferrite core. Kudos and atta-boy! How counter-intuitive and amazingly interesting to discover that the air core is sooo much superior. I am glad that you will repurpose the wood base, yet again. I understand that 3D printing a base is super convenient, but I find it cold and barren of nostalgia. Even the termination thread on the winding is better than glue, or tape, in that regard. And, I like the "ANT" and "GND" labels, stamped in previous boards. I guess I am just old and sentimental. Either that, or I am young, hip and really into steam-punk... grins... Yeah, I really love the solid wood base (not plywood.)

[@tsbrownie]

Thank you. I've got something in mind for it; still waiting on parts. We shall see. Yes, the 3D printer covers up my lack of woodworking skills. It's not beautiful (but there is wood filament that has real wood in it and shows changes in color like wood. Hmmmmmm.) Most people who want to do this can probably see what I've done and recreate it in wood. I like the steam-punk idea. Of course crystal radios are already kind of steam-punky as-is. Actually I could change the 3D printed shapes into plumbing-looking stuff and print it in copper color! OK, we went through that already.

[@franzliszt3195]

I'm not convinced air core is better, yet. A lot of flux is lost between the air core windings that are otherwise captured by the ferrite core.

[@travismoore7849]

I saw you were supposes to us 26swg on a ferrite for a crystal radio. They used 100 turns. So I don't know about that. I hear litz is the best wire to use.

[@migalito1955]

Thanks, I almost indepently assembled a similar ferrite core crystal radio that had little sensitivity. This one wins hands down, but I'll give the air core a go instead.

[@tsbrownie]

It seems that ferrite cores and variometer based radios are not suitable for unamplified, unpowered radios. Contesters use air cores and now I see why.

[@erikdevriese671]

I am surprised you got such poor results with the ferrite rod crystal set. I built my first crystal radio (Philips Pionier 1) when I was 16, connecting an antenna of 10m and using the central heating radiator as an earth. I could hear at least 6 AM stations with acceptable selectivity and volume. The coil is wound around a ferrite rod (#62 material), has 3 x 16 windings 0.5mm and the variable capacitor is 365 pF. Looking at your coil I wonder why you need so many windings. I think the section of the variable capacitor you're using has too little capacity. Do you use both capacitors in parallel? Later I rebuilt the crystal set using thick litz wire and this gave markable improvement in sensitivity. It its also worth experimenting with the tabs on the coil. Depending on local circumstances, it might be worthwhile to switch the antenna tab and the diode tab. Improvements can also be obtained by choosing different diodes or even crystal earpieces! The old 0A79 diode is almost unobtainable now but is still is more sensitive than modern germanium diodes like the AA119. Here's a link to a pdf of the manual. It's written in Dutch but I think the drawings are self explanatory. pa3esy.nl/Philips/Bouwdozen/pionier/pdf/pionier001.pdf

[@tsbrownie]

I will have to take a close look at the diagram. Thank you. I was also surprised how poorly the one I made worked. If you have several stations nearby, it would probably be OK, but if you're in a place like the middle of the US where stations are spread out, then it seems to be too inefficient to work with weaker signals.

[@adnacraigo6590]

I am thinking that you may be correct about the ferrite consuming some of the signal. I think of it as if the coil were wrapped around a metal cylinder of sorts.

[@tsbrownie]

I agree. The people who do crystal radio contesting use air core coils.

[@franzliszt3195]

I had though air core was used because it was required by contest rules?@@tsbrownie

[@jordanch68]

What happens if you ground the ferrite rod?

[@tsbrownie]

Probably not much. Ferrite is a poor electrical conductor. I touched the rod while using it and that would be an OK ground, and there was no difference, so....

[@franzliszt3195]

Well, I wonder about your ferrite core. What is the highest frequency station you get on it?

[@tsbrownie]

1600 kHz. I tested it with a frequency generator and scope and it looks pretty efficient.

[@franzliszt3195]

If I recall, in a vid you said the relative permeability was 1000. I would think it would have blown the air inductor out of the water. Strange. Is the diode reversed? The diode white bands look orientated differently on the two recievers.@@tsbrownie

[@tsbrownie]

@franzliszt3195 The relative permeability varies from 10s to thousands, so unless you order from a mfg or qualified distributor, you rarely get that number. I don't recall the formula for it and how it's related to Q. I'm sure there must be different qualities of the stuff as well. Too many variables and not enough rock solid info.

[@superrodder2002]

There are different mixes of ferrite and some are better at AM frequency than others. The wrong mix of ferrite can have a dampening effect at some frequency and not at others

[@tsbrownie]

True. The ferrite I used was supposed to be from AM radios, but who knows when you order stuff from online in unmarked packages.

[@vintagetransistorRadio.Radio.h]

Vooo thanks for sharing ❤️ 👍 🙏 😊 ❤❤❤❤❤❤❤❤❤❤❤

[@tsbrownie]

Thanks for watching

[@hobbyrob313]

HOOWWWWwww just this: be careful not to place the two coils too close together!!!!!! it may be that one is disrupting/pulling away the signal from the other. (like a kind of dipmeter!) And have you also tried replacing the diode alone? . well, don't put it aside, that's such a shame! I'm glad you're trying to figure out what's wrong. (I'm curious now too! What makes the RX insensitive?) Healthy and Friendly Greetings from here! Rob.

[@tsbrownie]

Thank you. I used to go on business when I was younger and single. Now I'm married with children. ;)

[@hobbyrob313]

Hello again! I would say divorce and go back to the Netherlands again! ;-) LOL Healthy and Friendly Greetings again! Rob

[@tsbrownie]

@@hobbyrob313 I'll have to ask my wife if that's OK. ;)

[@tenlittleindians]

It does kind of make sense that your air core kicks out more volume. The only energy is coming through the air into the wire. The radio with more wire has more power. Those old radios in the 20's ran long 100 foot or so wires out of windows to high up in tree trunks or the side of barns to maximize input power. Now you got me wondering if those early crystal sets wound on Quaker Oats cereal containers were even better because they had even bigger windings to absorb radio energy? There were a lot of failures trying to build those old published Quaker Oats radio designs and that's because modern cereal boxes are now smaller in diameter which threw off all the winding calculations. Someone figured that out and got a modern sized box to work by adjusting the windings but I don't remember anyone doing a comparison between a full sized box and a modern smaller sized box. Unfortunately only the collectors with full sized boxes have the radios to test with.

[@y_x2]

You should measure the Q factor.