Winter 2024/25 crystal radio.
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| It`s crystal
radio season again with early darkness so here my this winter x-tal radio
with new coil. |
| Do not ask the
price of this radio,... you do not want to know. R40C1 toroids more then $4.00/piece, litz $40/60ft. And all the PTFE and other parts. Same for the antenna tuner side. |
| I`ve made a
High Q coil using those R40C1 toroids. To be correct, a contra-wound one
using 660/46 Litz. I used 25 of these separated by PTFE foil. Stands are PolyPropylene. Coil value in series 221µH, parallel 58µH. |
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| Radio is build onto a polypropylene breadboard
(25x37cm) you can buy in a store for kitchen supplies. I use the
boards also to cut them in pieces to make parts out of it. The coils serial / parallel switch is made out of PTFE, same for the diode selector switch. The diodes and coil switch are switched using reed contacts and neodymium magnets. There can be a selection of differend diodes, or using more magnets two diodes or more in parallel. Vernier reduction is 1:50 from a General Electric drive. A wormdrive rotating a slack free gear. Connected using a nylon round rod towards the variable capacitor, I do not have PTFE or PP rod. Everything bolted together using nylon screws. Audio transformer can be connected directly to the diode surfboard and capacitor out connection using M3 thumbscrews. Output of diodes are all connected together and copper/brass parts in the selector are silver plated. The coil is as mentioned made using 660/46 Litz. But when connected in parallel it`s one coil 1320/46. To connect it to the variable capacitor I used from the switch to the variable capacitor 1300/44 Litz. Connection from capacitor to diodes and audio out I used 660/46 Litz. Litz screwed to terminals using brass cable ring lugs crimped onto the litz and soldered using lead-free solder with silver in it. And a piece of heat shink on it. |
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| Same for the tuner section. Everything bolted
onto a PP breadboard. Here a 25x R40C1 toroid coil, but now one single
coil with a value of 221µH using 660/46 litz. Same type of variable cap
and reduction drive as the detoctor stage. Included a 170pF antenna tuner capacitor. All wires in the tuner 660/46 Litz. Below the complete setup including the audio transformer unit. Still in the making is a newer audio transformer unit with 16/32Ω out and 2 or 3MΩ input impedance. |
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| Here the Q measurement of the antenna and
detector stage. Antenna tuner Q=1513 at 530Khz, Q=908 at 1004Khz, Q=588 at 1407Khz Detector measured in serial setting (221µH) is Q=1160 at 530Khz, Q=560 at 1400Khz Detector measured in parallel setting (58µH) is Q=804 at 1044Khz, Q=733 at 1600Khz |
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About this coil and Q-values. But,...If you make a nice job creating a spider using 660/46 litz I think the spider won`t be any worser then this expensive toroid coil. In my opinion the toroid coil is to expensive to get real gain compared to a spiderweb coil. The experiments Mr. Han Hong did were worth to try to get a Q2000 coil. But drying the coil for hours and measure it using a Q-meter with a holy grail capacitor in it isn`t a real world crystal radio with readily available parts. I`m not gonna rip a Q-meter just for the variable capacitor. I would love to see Mr. Han Hong`s real world working crystal radio and measurements. |
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For the difference in Q between the antenna tuner coil and the detector
coil, although same capacitor and inductance is the serial/parallel
switch. This reduces the Q of the detector circuit. And a small part the
connection to the diode switch. I`ve noticed I can upgrade the capacitor even more. Discard the nuts/bolts through the ceramic parts and put some PTFE or Polypropylene bolts/nuts in it with a sheet of very thin PTFE (0.3mm) between ceramic and body. |
| Things to make are a Audio matching transformer
with more impedance, more then 1-Mega-ohm and a tap for the 100V
system speaker driver. And erect the 18meters tall fishing pole to make a new inverted L towards east. Results published here after newyear 2025. |
