Ramsey FM100B FM Transmitter

Operation

To change the broadcast frequency on your Ramsey FM100B:

1. Press and hold both FREQ UP and FREQ DOWN buttons simultaneously (this enters frequency setup mode).
2. Release the buttons.
3. Use FREQ UP to increase the frequency or FREQ DOWN to decrease it (in 100 kHz steps, 88.0–108.0 MHz range).
4. Tune a nearby FM radio to the desired frequency and adjust until you hear the carrier (quieting signal; no audio input needed).
5. Press FREQ UP and FREQ DOWN together again to exit and lock the frequency.

MRF557

The standard Ramsey FM100B kit does include the MRF557 transistor (Q6) as part of its final amplifier stage. The GAL5 IC (U6) functions as the exciter/driver, generating the modulated VHF signal and delivering a low-level output (a few milliwatts) through a 0.001 µF capacitor to the base of the MRF557. The MRF557 then provides the necessary gain and buffering through the PI network to achieve the FM100B’s standard output of approximately 25 mW, compliant with FCC Part 15 regulations. The notion that the MRF557 is omitted in the standard model is a common misconception; it is an integral component in the standard configuration, not just in the optional 1W high-power upgrade (FM100BEX).

FM100B to FM100BWT Upgrade Kit

• 1 × MRF557 transistor (Q6 replacement – even though the stock one is the same part number, Ramsey always included a fresh one)
• 1 × 220 Ω ¼ W resistor (red-red-brown) → becomes R50
• 1 × 270 Ω ¼ W resistor (red-violet-brown) → becomes R64
• 1 × 100 pF 500 V silver-mica or ceramic disc capacitor → becomes C65 (replaces the stock 0.001 µF coupling cap)
• 1 × 15-turn molded choke, 1.5 µH (green body with brown-green-gold bands) → becomes L6
• 1 × Ferrite bead or small toroidal core + 6 inches of #28 enameled wire → to wind L2 (10–12 turns on the supplied core)
• 1 × Aluminum heat sink bar with two mounting holes (approximately 1.5" × 0.5" × 0.25") → HS1
• 1 × Small tube of heat-sink compound (silicone grease)
• 1 × FM100BEX instruction sheet (4 pages)

That is the complete, official contents of every FM100BEX kit Ramsey ever sold. No additional low-pass filter parts were needed because the stock FM100B board already has the harmonic filter built in. The ~30 dB gain jump comes from the new bias network (R50/R64), stronger drive through the 100 pF C65, and properly loading the MRF557 collector with the new L2/L6 network so it finally runs at its rated 1–1.5 W instead of the stock 25 mW.