Eric's "Crystal Radio Initiative" Challenge

[Jeff Pearson]

Did the calculations for this in January finally building it. 1340Khz. 1/8 inch tubing would be close to the ideal conductor but winding it with what I got right now. I think its 20awg

[LeeBob84]

Did the calculations for this in January finally building it. 1340Khz. 3/4 inch tubing would be close to the ideal conductor but winding it with what I got right now. I think its 20awg

Nice work

So i guess there is someone else out there who is doing this.. I was beginning to think I was the only person working on this

Best part is the way my neighbors look at this 5ft tall 4 ft diameter coil in my back yard. Some think its a chicken coop, some think its a fort for my kids, and I'm sure there are a few who think its some sort of ufo landing pad lol ... So far I have only met one person (in person, not on the net) who actually appreciates what this is actually designed for, and kinda understands what I'm talking about when I try to explain it, and he is an old military guy.

Hope u keep posting updates here. Will be nice to have someone to bounce ideas off of who is building one too.

[LeeBob84]

CRI Update

Did some calculating for my capacitor and have built a fairly crude looking but hopefully effective capacitor.IMG_0705.jpgIMG_0706.jpgIMG_0707.jpgIMG_0708.jpg The size of plates and how many is based on surface area of the secondary coil windings surface area. I calculated the surface area of the entire coil and adjusted my primary as well IMG_0709.jpgIMG_0710.jpg so that the surface area of all 3 components is within 100sq/in of eachother. This hopefully will cause the coil to resonate better. Also I have got the material now for the extra coil so I will be starting work on it next. This coil will be 1'6" tall and wide, it is a 1:1 ratio coil. Coil will be 90 turns with a wire length of 439'4" and close to 10awg so that is what i am going to use. Also I am changing my topload, The copper hemisphere I have built could possibly cause what looks like a dead short in the coil so i will be replacing it with 2 Toroids made from 6" aluminum foil ducting which will be capped with an insulator on each end to prevent this dead short in the coil.The big toroid will be around 3 ft in diameter and the smaller will be around 2 ft.

[Jeff Pearson]

CRI coil for 1340Khz Kvot

Corrected 1/4 wavelength= 142.25 ft.
using .7752 correction factor. 102% velocity factor X 76% burden factor.
I avoided all rounding till the end
Length per turn= 85.35 inches
At this point I figured for an octagon instead of a circle since my coil form is an octagon and I'm trying to be as accurate as possible so I calculated 10.67 inches per facet of octagon
Diameter of circle would be 27.18 inches
Height= 5.44 inches

The tuning seems to be right on. With topload and ground connected I can hear the radio station clearly through a regular crystal detector consisting of a germanium diode, demodulation capacitor, load resistor and crystal earpiece. It makes noise but unintelligable with no ground or top load.
At the moment the detector is connected across the secondary. I put together a simple amplifier using a LM386 IC driving a piezo element.
With the amplifier 1340Khz comes in clear with the secondary connected to nothing. When I add the top load the signal gets a little bit stronger and when I connect the ground the signal gets a lot stronger. I have tuned it up to 1510Khz by tapping the top load at the 16th or 17th turn. And I have accidentally tuned it down to 950Khz by adding a long ground wire one day when I didn't want to carry it out to the ground rod.
That's what I have done for testing so far. Oh and I did put a temporary primary on it with variable capacitor. There is a sweet spot where it raises the power of the secondary. Getting ready to rewind the whole thing. I am happy with the frame. More appropriate wire for the secondary and some 4 inch wide copper flashing for the primary coming soon.

Great Looking coil Leebob.

[Jeff Pearson]

Also, there is about a thousand foot deep rift in the earth between here and town "Rio Grande Gorge" I wonder what that does to the ground signal. I'm gonna have to take it to the other side of the Gorge and do testing there also

[LeeBob84]

CRI Update

Woo Hoo I won the CRI

Just want to throw out a special thanks to Aaron and Eric for the "Crystal Radio Initiative". It has been a time consuming build but very educational for me. Also a shout out to the annonymous donor of funds for the CRI Challenge. The funds are going to good use on the build.

I have now finished the extra coilIMG_0719.jpg and have added a precision adjustor to my capacitorIMG_0717.jpg IMG_0718.jpg Lol. Crude but effective. This is the beast with the extra coil and new toploadIMG_0716.jpg. I have pounded my holes in the grounding and am just waiting to receive funds for the aluminum to fill themIMG_0720.jpg. I have also decided that instead of using the 4awg copper, i am going to dig a thin trench about 12" deep and pour aluminum between all holes. I will also be pouring an extra eight holes in addition to these in the same pattern only 10 feet out. Also connected the same way. I am hoping i can get about 200lbs+ of aluminum in the ground. This should be effective as a good grounding system for now.

[LeeBob84]

Also, there is about a thousand foot deep rift in the earth between here and town "Rio Grande Gorge" I wonder what that does to the ground signal. I'm gonna have to take it to the other side of the Gorge and do testing there also

What is your ground?

[Jeff Pearson]

CKLW is a 50,000 watt, Class B, AM radio station . Is this the station your trying to pick up and have you done any receiving yet LeeBob. The local station I built for only puts out a thousand watts. I think maybe I could do pretty good by taking it to town and connecting to a fire hydrant for ground.

[Jeff Pearson]

ground here is dry sandy clay. I pounded a 4ft piece of rebar for a ground to start with. Then I tried my roof. I am building a concrete dome on top of rammed earth walls. There is a 3ft piece of rebar every 30 inches driven into the rammed earth walls to connect the bond beam to the metal skeleton of the roof. The CRI coil and the crystal radio both work better using this for ground than a standard ground rod. I have not made an actual ground plane yet but I do have the room to do so. the rammed earth walls are a 20ft diameter on the inside circle and the walls are about 30inches thick so the connection to earth is good as far as surface area goes

[LeeBob84]

CRI coil for 1340Khz Kvot

Corrected 1/4 wavelength= 142.25 ft.
using .7752 correction factor. 102% velocity factor X 76% burden factor.
I avoided all rounding till the end
Length per turn= 85.35 inches
At this point I figured for an octagon instead of a circle since my coil form is an octagon and I'm trying to be as accurate as possible so I calculated 10.67 inches per facet of octagon
Diameter of circle would be 27.18 inches
Height= 5.44 inches

The tuning seems to be right on. With topload and ground connected I can hear the radio station clearly through a regular crystal detector consisting of a germanium diode, demodulation capacitor, load resistor and crystal earpiece. It makes noise but unintelligable with no ground or top load.
At the moment the detector is connected across the secondary. I put together a simple amplifier using a LM386 IC driving a piezo element.
With the amplifier 1340Khz comes in clear with the secondary connected to nothing. When I add the top load the signal gets a little bit stronger and when I connect the ground the signal gets a lot stronger. I have tuned it up to 1510Khz by tapping the top load at the 16th or 17th turn. And I have accidentally tuned it down to 950Khz by adding a long ground wire one day when I didn't want to carry it out to the ground rod.
That's what I have done for testing so far. Oh and I did put a temporary primary on it with variable capacitor. There is a sweet spot where it raises the power of the secondary. Getting ready to rewind the whole thing. I am happy with the frame. More appropriate wire for the secondary and some 4 inch wide copper flashing for the primary coming soon.

Great Looking coil Leebob.

Thanks Jeff

Your coil sounds like its coming along nicely. How far are u from the station u are tuning for. And as for the rift it shouldn't effect your signal to badly as it is still connected down there somewhere. I am about 25 miles from the radio station which i am trying to recieve and have a hard time to get the station on my Iphone doc with the antenna at exactly 90 degreesIMG_0721.jpg to the station signal. The interesting thing i accidently discovered after messing around with the coil yesterday is that with it plugged into just the house ground and the extra coil and topload in the circuit i was able to lay the antenna coil from the iphone doc flat on the tableIMG_0722.jpg and the station would come in clearly. I thought at first that maybe it was just the weather at the time or something but as soon as i unplugged it from ground the station would cut out.

[LeeBob84]

ground here is dry sandy clay. I pounded a 4ft piece of rebar for a ground to start with. Then I tried my roof. I am building a concrete dome on top of rammed earth walls. There is a 3ft piece of rebar every 30 inches driven into the rammed earth walls to connect the bond beam to the metal skeleton of the roof. The CRI coil and the crystal radio both work better using this for ground than a standard ground rod. I have not made an actual ground plane yet but I do have the room to do so. the rammed earth walls are a 20ft diameter on the inside circle and the walls are about 30inches thick so the connection to earth is good as far as surface area goes

Just as a suggestion for when u put in your ground network, maybe run some pvc pipe beside ur ground rods and wires with holes drilled so u can flush an electrolitic solution down to the conductors to help them. I have done this before with gardens for feeding the plants. It will saturate the soil and the conductor giving u a larger conductive surface area. I was going to do this with my system but my water table here is less than 4' from the surface so it is kinda pointless here.

[LeeBob84]

I would like T-Rex to join the conversation if he has any suggestions?

[Jeff Pearson]

Sounds like the Iphone picks up the resonance from your CRI coil. NICE!!

[LeeBob84]

CKLW is a 50,000 watt, Class B, AM radio station . Is this the station your trying to pick up and have you done any receiving yet LeeBob. The local station I built for only puts out a thousand watts. I think maybe I could do pretty good by taking it to town and connecting to a fire hydrant for ground.

No this is the station I am trying to tune too is CJBQ 800 in belleville ontario. 800 am cjbq - Google Maps.pdf it is a 10,000 watt station.

[Jeff Pearson]

Looking into what to purchase to wind the secondary with and am really getting confused. I am looking for a 6 AWG size conductor. 1/8th inch copper tubing and 6 AWG welding wire cost about the same. The welding wire is made of many small conductors so should be good for skin effect. I saw some 6 AWG Litz wire on Ebay made of magnet wire but that guy didnt have a long enough length. Might look into a spool of that. A cheap solution is 1/8th inch wide copper tape. Lots of surface area low mass???. And the there is the suggested teflon insulated coax. What would i be looking for in coax that has an outer conductor the right size??? Any suggestions and or pros and cons of each choice would be much appreciated. Today I got an antenna 29 feet into the air and am messing with a standard crystal radio.


oh and I am 15.87 miles away from my thousand watt station with the rift a little closer to me as per attachment on post #38..........and yes have done the PVC pipe trick for trees out here in the desert I will do that for my ground rods when I get them.