For Assemblying this FM transmitter kit, a beginner will take about 3 hours to tinker the issuer, an electronics hobbyist will have built in about 30 minutes.

FM Transmitter Construction
It is not necessary to drill the transmitter PCB. All components will be soldered to the plate with their legs folded, like this:
The two transistors and the LEDs are polarized:
The transistor has a flat side, the LED a foot longer than the other is the anode (A), the other is the cathode (K). The audio cable (minijack) must be transformed from a stereo cable into a cable.

Mono Sound:
Soldering together the white and red cables, leaving aside the yellow cable (mass). The frequency setting will be turning the variable capacitor gently with a screwdriver or thin cardboard but rigid.

FM Transmitter Parts List

• 1 Ohm resistor 510 (green – brown – brown)
• 100 resistor 1 kOhm (brown – black – yellow)
• 1 MOhm resistors (brown – black – green)
• 1 capacitor 0.1 uF (0.1)
• 1 nF capacitor 47 (0.047)
• 1 capacitor 4.7 pF (479)
• 2 pF capacitors 22 (22)
• 1 variable capacitor 1.5 pF … 15
• 2 transistor BF 246 (F246A)
• 1 red LED
• 1 audio cable (minijack)

Source: Pi-Radio Mini-Shop

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!

C4 is a small, screw-adjustable, trimmer capacitor. Set your FM receiver for a clear, blank space. Then, with a non-conductive tool, adjust this capacitor for the clearest reception. Although this transmitter is designed for the FM broadcast band, it can be tuned to 2 meters, and other VHF bands by changing values of C4 and L1.

L1 is 9 turns of #22 gauge solid wire (air-wound) 1/4 inch diameter coil. Use a 1/4 inch diameter bolt and wrap the wire in the threads. After mounting the coil, back out the bolt.

C1, C2, C3, and C5 are ceramic type capacitors, preferably npo (low noise) or equivalent. However, you can use any type you have around, but do not use electrolytic or tantalum capacitors.

A 2N3904 transistor was used for Q1 and Q2. The 2N3904 is a general purpose silicon NPN bipolar transistor used for switching and amplifier applications. However, you may substitute the 2N3904 with a 2N2222 or a 2N3906, these are also general purpose transistors.

The antenna is 8” to 18” of any type wire.

Try to keep all leads as short as possible to prevent stray capacitance.

Transmitter Parts:
R1, R4, R6 10K resistor
R2 1Meg resistor
R3 100K resistor
R5 100 ohm resistor
R7 1K resistor
C1, C2 0.1uf capacitor
C3 0.01uf capacitor
C4 5 – 30pf variable capacitor
C5 4.7pf capacitor
Q1, Q2 2N3904 transistor
L1 9 turns of #22 gauge
Microphone Electret Mic
Circuit Board
Battery Clip

You can buy these parts at any electronics store.

Source: Free Kit Plan – FM Transmitter