BF-900 Oscillator (VFO) devresi

Konusu 'Fm Verici Devreleri' forumundadır ve guclusat tarafından 17 Mayıs 2010 başlatılmıştır.

  1. guclusat

    guclusat Tanınmış Üye Süper Moderatör

    14 Haziran 2009
    Ödül Puanları:
    Oszillator mit BF900

    Hier der Originaltext aus dem www, weiter unten gibts dann noch eine Erweiterung der Schaltung, einen Buffer / Vorverstärker für den Oszillator.


    This package contains the schematic and a PCB-layout for a FM oscillator using the BF900 Dual Gate Mosfet, and can be used between 90 and 110 MHz. Specific things about this oscillator is that it has very low noise, and it is very stable. If you use proper buffering, a PLL shouldn't be necessary any more (although it is ofcourse possible to use one).

    The frequency is first set by trimmer C4. Adjustments can be made with R8 (VFO range is about 4 MHz).

    Some testing gave me next results:

    (Frequency = 100 MHz; Output = 50 Ohm Dummy (20 * 1K/1W par; homebrew)

    Input = Sweeposcillator 0.5-55 kHz (Stereo Coder)

    Power Supply : 15 V DC ('no ripple')

    Input Current : 50 mA

    RF Output : 55 mVpp

    Freq. Deviation : 0.005 MHz (after 10 hours; the deviation had taken place during the first hour, after that no deviation)


    Use a good quality PCB, the other side is copper, make some connections between the two sides. Build the oscillator in a RF-proof casing, use good connectors and cable, and be aware of all the other RF-rules of building.

    To mount the BF900 a hole (diameter about 6 mm) must be made where the casing can hang in. I myself had problems with the 'other side copper' thing, because my oscillator wouldn't turn on (not too enough noise?? just kidding). It was solved when I removed the copper under the BF900 (about 1 - 1.5 cm diameter).

    If someone has an explanation for it, let me know...

    Don't use other kind of resistors!

    You could use a zener-stabilisation instead of the 7800-regulator. The only problem is that it could cause a DC-ripple on the oscillator, and that will be noticed as humm. A voltage regulator isn't so expensive, so don't cut down expenses on it.

    Instead of the BF900, a BF905 or BF907 can be used without any problems. Maybe a BF981 would do also, but that I haven't tested.


    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: (at least untill October 1994)

    Ofcourse you can use the same adress for other questions or comments on this schematic.

    Eric van Gorkom





    80 * 55 mm

    Component list of the FM Oscillator with the BF900


    (All resistors are metalfilm types except R1 which is a carbon resistor)

    R1 : 47k, 1/8 W
    R2 : 47k, 1/8 W
    R3 : 47k, 1/8 W
    R4 : 100E, 1/8 W
    R5 : 220k, 1/8 W
    R6 : 100k, 1/8 W
    R7 : 150E, 1/8 W
    R8 : 10k, lin. pot

    C1 : 100 nF Multilayer or ceramic
    C2 : 4.7 pF ceramic
    C3 : 100 nF ceramic (1 or 10 nF will do also)
    C4 : 40 pf trimmer
    C5 : 4.7 pF ceramic
    C6 : 10 pF ceramic
    C7 : 22 pF ceramic
    C8 : 1 nF ceramic
    C9 : 1 nF ceramic
    C10: 100 nF ceramic
    C11: 100 nF ceramic
    C12: 100 nF ceramic
    C13: 47 uF/25V
    C14: 1 nF ceramic

    L1 : 4 wdg, dia 8 mm, 1 mm CuAg, space 1 mm;
    Mounted 8 mm above PCB (Leads are 4 mm)
    L2 : 6-hole ferroxcube wideband HF-choke (5 wdg)
    L3 : 6-hole ferroxcube wideband HF-choke (5 wdg)

    Q1 : BF900
    D1 : BB405,BB102 or equal (most varicaps with C = 2-20 pF (approx) will do)
    U1 : uA78L08, uA7809, uA7810 or equal (MC78LXX, UC78LXX etc

    Ekli Dosyalar:

    Son düzenleme: 29 Ekim 2017
Benzer Konular - 900 Oscillator (VFO)
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