Long Range FM Transmitter
Presented here is a Long Range FM Transmitter. This circuit is a super-sensitive, mini-powered FM transmitter consisting of a RF (radio Frequency) oscillator section interfaced with a high sensitivity, wide pass-band audio amplifier and capacitance mike with a built-in FET (Field Effect Transistor) that modulates the base of the RF oscillator transistor. Transistor Q1 forms a relatively stable RF oscillator whose frequency and is determined by the value of coil L1 and turning capacitor C4.
Long Range FM Transmitter Circuit
This circuit is a circuit diagram fm transmitter. This circuit is somewhat different from the previous fm transmitter circuit. Transmitter circuit described here has the additional RF power amplifier stage, after the oscillator stage, to increase the power output of 200-250 milliwatts. With a good matching 50-ohm ground plane antenna or multi-element yagi antenna, this transmitter can provide a good enough signal strength to a distance of about 2 kilometers.
Low Pass Filter For FM 88-108 MHz
Filter used for eliminate unwanted harmonic frequency at second and third. Notch filter, Band Pass Filter (BPF), and High Pass Filter (HPF) sometime combined in constructing LPF design.
Schematic below for FM Broadcast Lowpass Filter 88-108 MHz. It has been tested with a good result.
Note : Make the coils at 74 nH and trim them to adjust exact value.
Low Power FM Transmitter
This low power fm transmitter is designed to use an input from another sound source and transmits on the commercial FM band. This low power fm radio transmitter it is actually quite powerful.
The first stage is the oscillator, and is tuned with the variable capacitor. Select an unused frequency, and carefully adjust C3 until the background noise is removed.
The schematic you find here comes from another site on the internet, but because it's on so many sites, we don't know who actually designed it. However it's a nice one.
C1,C4 22pF cer.
C2,C3 51pF cer.
L1,L2,L3 #18 bus wire, 1/4"diameter, 3 turns
* Form the leads from the capacitors as shown in the little figure below. Then solder them from the pad to the outside ground area.
* Be sure that the turns from the coil are seperated by the same distance as the diameter of the wire
* Form the leads from the coils as shown in the little figure below. Then solder them in place.
* Place the filter in a metal box, with rf-connectors on both ends ( SO239(=PL259), BNC or N-connectors)
MC145170 PLL FM Transmitter
In order to simplify the transmitter design, we've used the new pll circuit from Motorola :the MC145170.
This PLL includes the prescaler and a serial standard bus called SPI.
Micro Spy PLL FM Transmitter
This micro spy PLL FM Transmitter transmits on the 160MHz frequency (if we use a 40MHz quartz) and therefore can be listened through a receiver tuned on this frequency. This circuit can be used to on various frequencies, for example on the FM band 88-108 just modifying some components, among which the quartz (25MHz).
Voice is detected by an electret microphone, then it is amplified and filtered by U1 pass-band in order then to be modulated from the carrier section, where through the varicap diode it "mixes" with the frequency generated by the quartz, that guarantees an adapted stability. Practically the modulating voltage is obtained applying the audio signal to the resonating circuit varicap diode that determines the carrier oscillation. The carrier frequency (160 MHz) must be greater than the modulating frequency (300-3300 Hz) audio band.
The transmission is on the fourth harmonic, therefore 160MHz, the oscillation frequency of the driver RF transistor Q1.
A small calibration is allowed acting on the L1 inductance and the C1 Trimmer Capacitor.
Micro Transmitter Bug
Presented FM transmitter bug is built using BF414 / BF324 / BF606 transistor. The 30cm antenna has a range of about 30m in the building, more in the open field. Power supply 2x AAA batteries have been used with voltage of 2.75 V. I added resistor 10K in parallel with 1.5pF capacitor so that the system works well when connected to an external source (mp3 player / computer). On the computer I had to reduce sound to about 35% of capacity, so that I do not have clipping. I managed to improve transmitter stability with simple shielding. The coil is 5 turns of enameled copper wire wound on 1 mm ø = 5 mm.
Mini FM Broadcast Transmitter
Build your own simple mini FM transmitter. This fun project will show you how to build a mini broadcasting transmitter that can transmit an audio signal up to a quarter mile to any FM receiver. It's easy to build and a good learning experience. It serves as a hands-on learning tool for students or anybody interested in electronics. Having a range of up to a quarter mile, it's great for a house security system, baby monitoring device or simply a listening gadget that you can place anywhere!
Mini FM Radio Broadcast Transmitter
Have you ever wanted to broadcast your own radio station within your neighborhood? This small and simple 87-108MHz FM transmitter is the toy that geeks have always wanted. This tutorial includes the PCB layout and the schematics. It has a range of up to 1/4 mile or more. It's great for room monitoring, baby listening and nature research.