1km Coiless AM transmitter

Okay so I've been working on a way to make an AM radio transmitter without the use of any inductors chokes and stuff. Juat plain old op amps. A TL072 should do just fine. Whatever else you have at hand will also work but be sure to check the maximum frequency it can operate. For the sake of the simulation the carrier frequency is 75Khz. That won't do you any good. On the carrier generator the RC feedback must be 100pF and 10k potentiometer. The potentiometer also provides easy tuning throughout the whole AM spectrum (500Khz-1.5Mhz). The MOSFET is any general purpose low power mosfet. Now a little disambiguation on the power stage. Usually class AB amplifiers are rare in RF circuits but for the sake of inductorless circuit i used one. It seems to be working perfectly and is quite power friendly. 50% efficiency is normal for these kind of amps. The power transistors can be of any type. Just look for >0.8W transistors @2Mhz. I think even TIP41/TIP42 will do. The output power of the AM transmitter is a little above legal rating at 0.57W which will most probably cast a range of a km or so, so i recommend setting a limit to the circuit by lowering the supply voltage to 9V. At 16V i estimate the output will reach above 1W. Interestingly enough this veeery simple design seems to be fixing a lot of issues that occur in RF circuits. For instance AM transmitters most often are not simple to tune to different frequencies. Especially quartz stabilised ones but this one can tune into the whole AM bandwidth without needing to change output resonance filters and stuff. 2nd usually leaving a transmitter antennaless is destructive for the output device but class AB amps don't suffer that problem. Also this circuit should have a broader frequency response than usual but still AM is far inferior to FM. If you want Hi-Fi transmitter this is not your thing.

published 10 years ago