Homebrew Broadcast Warehouse Based LPFM Transmitter
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I lifted the trace on LED2, it's mounted under the board. Pre-emphasis caps are polystyrene. Limiting LED3 is panel mounted. Set the limiting adjust (20k single turn pots) to maximum (fully clockwise). Mount board on nylon standoffs to limit microphonics/ground loops.
Stero/mono switch is panel mounted. Onboard SSM2143 is jumpered (not needed). Onboard pre-emphasis is disabled - enabled on limiter. Post 15 kHz filter clipping is on. Pilot level is adjustable via a 10k pot inbetween R20 and C24, replace R20 with a 6.8k. Replaced the final two op-amps with LT1055. Mount board on nylon standoffs to limit microphonics/ground loops.
Pre-emphasis is disabled. Replaced LF351 loop filter op-amp with a OP27. Audio/loop filter resistors are 1% metal-film, where available. 1/8 watt resistors replaced with 1/4 watt to improve heat dissipation (probably overkill). PLL lock LED panel mounted (LEDs rule). Parallel 1.2k LED limit resistor for brighter LED. Ferrite on the LCD control cable. Set dipswitches to 555 (?) for front mount LCD frequency control (a must for electronic warfare apps). Glue down RFT1. Mount board on nylon standoffs to limit microphonics/ground loops.
Rack mount case from old cable TV video equipment. 12V for the audio section, seperate 15V regulator for the exciter board. Keep RF output and exciter audio input well shielded (telfon coax and metal RCA plugs). Front panel isn't done yet, will add LCD bezel and blue power LED. LED holders from Radio Shack. Not shown is an external AC line filter. Ferrites on all control/power lines.
Broadcast Warehouse PLL PLUS manual My own version