: Repository-circuits

Posted on Feb 6, 2014

This package contains the schematic for an FM transmitter with 3 to 3.5 W output power, and can be used between 90 and 110 Mhz. Although the stability Although the stability isn't so bad, a PLL can be used on this circuit. This is a circuit that I've build a few years ago for a friend, who used it in combination with the BLY88 amplifier to obtain 20 W output power (for that schematic, get the LINBLY88.EXE file). From the notes that I made at the original schematic, it worked fine with a SWR of 1 : 1.05 (quite normal at my place with my antenna). He didn't use it for stereo broadcasting, but that shouldn't be a problem. BTW: I'm sorry about the mess my OrCAD Annotate made of the component numbers. 2) Components/Hints I don't have a PCB-layout for it, but as I remember I've made it on a normal RF-testing breadboard (with one side copper). Make some connections between the two sides. Build the transmitter in a RF-proof casing, use good connectors and cable, make a shielding between the different stages, and be aware of all the other RF-rules of building. Q1 and Q5 should be cooled with a heatsink. The case-pin of Q4 should be grounded. Adjustments: C24 is for the frequency adjustment. The other trimmers must be adjusted to maximum output power with minimum SWR and input current.

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Component list of the 3 - 3.5 W FM transmitter (Type 1) Resistors: (All resistors are 1/4 W carbon or metalfilm types) R1 : 10k R6 : 680E R11: 680E R2 : 22k R7 : 150E R12: 100E R3 : 22k R8 : 100E R13: 3.9k R4 : 10k R9 : 68E R14: 10k R5 : 3.9k R10: 6.8k R15: 10k Capacitors: C1 : 4.7 pF ceramic C11: 100 nF ceramic C21: 40 pF trimmer C2 : 100 nF ceramic C12: 100 nF ceramic C22: 40 pF trimmer C3 : 100 nF ceramic C13: 82 pF ceramic C23: 40 pF trimmer C4 : 100 nF ceramic C14: 60 pF trimmer C24: 40 pF trimmer C5 : 100 nF ceramic C15: 27 pF ceramic C25: 5 pF ceramic C6 : 10 nF ceramic C16: 22 pF ceramic C7 : 100 nF ceramic C17: 10 uF/25V C8 : 60 pF trimmer C18: 33 pF ceramic C9 : 10 nF ceramic C19: 18 pF ceramic C10: 10 nF ceramic C20: 12 pF ceramic Inductors: L1 : 5 wdg, dia 6 mm, 1 mm CuAg, space 1 mm L2 : 6-hole ferroxcube wideband HF-choke (5 wdg) L3 : 6-hole ferroxcube wideband HF-choke (5 wdg) L4 : 1.5 wdg, dia 6 mm, 1 mm CuAg, space 1 mm L5 : 6-hole ferroxcube wideband HF-choke (5 wdg) L6 : 1.5 wdg, dia 6 mm, 1 mm CuAg, space 1 mm L7 : 6-hole ferroxcube wideband HF-choke (5 wdg) L8 : 1.5 wdg, dia 6 mm, 1 mm CuAg, space 1 mm L9 : 6-hole ferroxcube wideband HF-choke (5 wdg) L10: 8 wdg, dia 5 mm, 1 mm CuAg, space 1 mm Transistors: Q1 : 2N3866 Q2 : 2N2219A Q3 : BF115 Q4 : 2N2219A Q5 : 2N3553 Others: D1...

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