- This topic has 1 reply, 1 voice, and was last updated 2 years, 4 months ago by Guenther.
2020-February-26 at 07:51 #8334GuentherSpectator
The good old ZN414 made by Ferranti (and their clones MK484, TA7642, LA1050, …) is a powerful AM receiver up to ~ 2 MHz / mcps with 10 transistors and AGC. The application was designed for 1.5V and solar powered mini-radios for AM BC and known since 1973.
It is important that the voltage is max. 1.5V, so I decided to build a special block with voltage stabilization and the always (!) required components to reduce the amount of additional Lectron blocks.
A simple radio circuit with AF amplifier and loudspeaker may look like this:
The LM386 block is a powerful amplifier, and between pin 1 and 6 can be soldered an electrolytic capacitor to increase the amplification (not on the photo / block cover). The tuner block is a multi-functional one for later / universal use.
A superhet can be easily established by simply changing my (well known) tuner block with a plugged-in silicon npn transistor and adding the IF filter block:
Now the ZN414 acts as an IF amplifier and demodulator and – together with the built-in AGC function – give best results.
Changing the AM BC tuner block by a SW tuner block shortwave stations can be received – depending on the used coils and varcaps, possible from 4 … 20 MHz / mcps. The amplifier (TDA7052) is prepared by me to have a long life… because the IC is for max. 6V, and an open input “kills” one or both output stages because of wild oscillation. So the input is blocked with 10kΩ to Ground, and the voltage has 2 diodes 1N4001 serial, together with a 100µF cap to Ground.
This tuner version was a prototype, meanwhile the ready-built block looks like this (photo is the pnp version, changing a few parts = npn):
The SW tuner block has 2 simple coils, no ferrit antenna – these cannot be used for higher frequencies than 12…14 MHz / mcps. These tuners have 2 equal varcap packs, e.g. 2 x 345 pF, because receiving and oscillator frequency differ only by 455 kHz / kcps.
Without ferrit antenna all receivers need a long antenna wire – depending on the actual location, perhaps a good “earth” connection, too. In the cold seasons the reception of sw stations is much better.
AM BC varcap packs have 90 + 180 pF, so a combination of AM BC and SW reception is not possible.
For the adjustment of superhets please refer to existing literature – otherwise wait for my article showing my simple AM modulator with one pnp Germanium transistor 😉
Always good reception!
- This topic was modified 2 years, 4 months ago by Guenther.
- This topic was modified 2 years, 4 months ago by Michael. Reason: Changed font and size styling for easier reading
2020-February-28 at 06:53 #8400GuentherSpectator
… I forgot to add another SW receiver block – the NE612 as mixer with a wideband input and oscillator circuit (variable capacitor + SW coil) together with the above ZN414 (or clone) as IF amplifier:
The output with speaker or my special block to use (stereo) headphones as parallel (mono).
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