#USE TANK CIRCUIT AS TIMER DRIVER#
Coil can be wound around a Screw driver (with the same diameter as that of the coil). Then only the inductor resonates in the 88-108 band FM frequency. The length, inner diameter, number of turns etc are the important parameters to be considered while making the inductor. Even the Hook up wire can be experimented. Inductor for FM transmitter can be made from enameled copper wire with gauge from 22 – 26 SWG ( Standard Wire Gauge). The purely reactive elements, the C (Capacitor) and the L (Inductor Coil) simply stores energy to be returned to the system. T he name ‘Tank’ circuit comes from the ability of the LC circuit to store energy for oscillations. The FM transmitter needs an oscillator to generate the radio Frequency (RF) carrier waves. The most important part of an FM transmitter is the Tank Circuit. Coil diameter, length, number of turns and gauge of the wire used for coil winding. Transmitter frequency, output power and range of transmission.ģ. These are the important parameters for the optimum performance of an FM transmitter.ġ. Length of the Antenna used to transmit the frequency. Even a slight change in the Coil specification or slight change in the Variable capacitor value can shift the harmonic frequency instead of the 88-108 MHz FM band.Ģ. Tuning of the FM transmitter to the desired frequency. The performance of an FM transmitter depends on two important aspects.ġ. It is necessary to consider a number of factors during the design of an FM transmitter. See the important aspects of FM transmission and the Design of an FM transmitter using IC UPA 1651. Usually 87.5 – 108.0 MHz is used to transmit and receive the FM signals.
The broadcast band of FM falls within the VHF part of the Radio spectrum. Change it to 63 ohms and the overshoot will vanish.The Frequency Modulation ( FM) system conveys information over a carrier wave by varying its frequency. Change the DC resistance to 50 ohms and you'll only see a slight overshoot like you have. You'll clearly see four cycles of ringing before it decays into insignificance. So you can see what you are up against, here's a LTspice sim with 11.5 ohms inductor's DC resistance.
#USE TANK CIRCUIT AS TIMER SERIES#
Measure its DC resistance and post it, and given the inductance and capacitance, we can calculate if that is the case, from the equation for the series critical damping condition: R 2=4L/C which gives fractionally over 63 ohms for your choice of a 1uF capacitor and a 1mH inductor. Therefore, its likely that your LC circuit is heavily damped, possibly over-damped, hence the lack of visible ringing. High value small axial inductors have considerable DC resistance. Some cheap USB scopes and handheld scope kits have very limited input voltage ratings. With a x10 probe it will be OK as long as the scope is rated for >15V max input. * Caution: If your scope isn't rated for >150V max input, the NE2 neon bulb will NOT provide adequate protection if you use a x1 probe. The traditional way to avoid contact bounce would be to use a mercury wetted relay, which can still be found NOS, but I wouldn't even entertain getting one unless it was a hermetically sealed miniature one. The biggest problem will be contact bounce. Assuming a positive supply,when you connect the inductor to the capacitor you'll get a sharp positive edge the scope can easily trigger on.
Put a NE2 wire-ended neon bulb (without a resistor) directly across the inductor to protect the scope * by clamping the back-EMF in case the inductor gets disconnected before the damped oscillation has died out. Connect a x10 scope probe to the non-grounded end of the inductor, so it doesn't load the charging circuit till you connect the inductor to the capacitor. For your 1uF capacitor, give it five seconds. Anything up to 200nF will pretty much fully charge in under a second through a 1 Meg resistor, which will have negligible damping effect on the LC tank circuit. Charge the capacitor through a high value resistor so you don't have to disconnect the charging circuit. Circlotron is on the right track, but rather than fumble around disconnecting the capacitor from its charging supply and transferring it to across the inductor, lets make it easy to work.