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= FM TRANSMITTER 3 - 3.5 W =
= Type 1
=
========Version 1.00=========
25-01-94
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.
3) Problems?
If you have certain problems, you have to try to solve them yourself first.
But if no solutions can be found you can contact me, so we can try to work it out. This circuit is build by me and it works.
You can also contact me if you have some interesting schematics or material, use E-mail: ericg@stack.urc.tue.nl (at least untill October 1994).
Ofcourse you can use the same adress for other questions or comments on this schematic.
Eric van Gorkom
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 : BB405, BB102 or equal (most varicaps with C = 2-20 pF (approx) will do)
U1 : uA78L08, uA7809, uA7810 or equal (MC78LXX, UC78LXX etc)