Tunable 555 Direct Conversion AM Transmitter

315

03:12:50

Filter gain drop off exponentially after the LC resonant frequency which is tuned at around 914 kHz

Transmitter designed for 540kHz to 1400kHz

Input is +-30mv

The local oscillator is realized using 555 as VCO, you can control the frequency by adjusting the voltage in CONT pin.

The message is mixed using H-bridge transistor driven by local oscillator, then the RF output is filtered  to reduce the harmonics.

published 6 years ago

hurz

6 years ago

i never heard about a direct conversion concept for a transmitter. For receiver yes, but transmitter??? Actually all transmitter are "direct" on transmitter frequency. So you transmitt on 540kHz you need an oscillator on 540kHz, right. Thats it. Indirect would be a special case to transmitt on 540kHz but start at 300 and then add missing 240 by mixing upto 540. Have you seen such a concept before? But this would be indirect and not direct. Something is missing ...

prinzrainer

6 years ago

When we went to some radio station during our educational tour they have IF prior to the final upconversion. I don't know the reason.

hurz

6 years ago

for receiver, right. But transmitter?

hurz

6 years ago

in early days of mobile phones, there where transmitter concepts to triple the output to the final transmitter frequency around 900MHz so they work controlled on 300MHz and with the third harmonic they transmitt. This can be seen as an indirect way to transmitt. And finaly they all have a vco directly on transmitter frequency, so no need to tripple. All todays transmitter are direct conversion in this sense.

zorgrian

3 years ago

He means to say DSB-RC (double sideband reduced carrier)

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