The Power Distribution Board is the first board that should be constructed. Having a power distribution board greatly simplifies the testing process as the various boards are built and put in operation. Without a power distribution board, the process of wiring and switching power to multiple boards (receiver subsystems) quickly becomes unmanageable.
The Power Distribution Board is a dual use board. As the ExpressPCB mini board service provides 3 boards, it makes sense to design dual use PCBs where possible. One population option provides power distribution for the Express Receiver. Two boards were built in this configuration, one used in the Express Receiver and a second one used on the test bench. A second population option provides a power supply for Paul Kiciak’s N2PK Vector Network Analyzer, built on a PCB from Ivan Makarov, VE3IVM. I highly recommend the N2PK Vector Network Analyzer (VNA) for anyone undertaking a receiver project such as this. The VNA was used to align the RF band pass filters and verify proper operation of the 9-MHz IF filter boards.
The Power Distribution Board configuration for the Express Receiver provides four connection points for the 13V unregulated supply, and eight connection points for the 12V regulated supply. Three of the unregulated 13V connection points are used to power the three Display and Control Boards. All other boards that require separate power connections are connected to one of the eight regulated 12V connection points. Regulation for lower supply voltages, e.g., 9V, 5V and 3.3V, is provided on individual boards as required.
Diode D1 provides reverse polarity protection. The power switched is connected to J2. The center pin of J2 is ground to support power switches with an integrated LED indicator as shown on the schematic. The power switched used in the Express Receiver was obtained from Sparkfun, part number COM-11155, a round rocker switch with a blue LED.
U1 is a Micrel MIC29150 high current, high accuracy, low-dropout voltage regulator. L1, C4 and C5 provide noise filtering for the regulated 12V supply. Ferrite beads FB1 through FB12 in combination with C7 through C18, respectively, provide RF filtering and isolation of each of the connection points to the unregulated 13V and regulated 12V supplies. LED 1 provides indication that the regulated 12V supply is operational.
The ExpressPCB file for the board can be provided upon request.
A regulated 5V power supply is populated on the Power Distribution Board for use with the N2PK VNA.
U2 is a Micrel LM2574 adjustable switching voltage regulator. This regulator was chosen for its high efficiency to minimize heating in the VNA. No heat sink is required as adequate heat transfer is provided by soldering all package pins to the PCB. Careful attention needs to be given to filtering the power supply lines to achieve the lowest possible VNA noise floor. C20 – C25 and L3 provide filtering of the LM2574 5V output. LED 2 provides indication that the regulated 5V supply is operational.
Refer to the RF Band Pass Filter page for information on the connectors J1 through J15.
All 470uF capacitors are 16V radial lead devices, Digikey PN P15342CT-ND.
Capacitor C19 is 330uF, 25V radial lead device, Digikey PN P15357CT-ND.
All 0.1uF capacitors are SMD 1206 style chip capacitors.
R1 and R6 are 1K and 240 ohm, respectively, 0.5W 1206 SMD resistors.
R3 & R5 are 2.2K and 6.8K ohm, respectively, 1% tolerance 1206 SMD resistors, that set the output voltage of the LM2574 switching regulator.
L1 and L3 are 22uH VHF chokes, Digikey PN 495-5590-1-ND.
L2 is a 470uH VHF choke, Digikey PN 495-5595-1-ND.
LED 1 & 2 are clear green LEDs, Mouser PN 645-598-8270-107F.
The version of the Power Distribution Board shown in the photos above includes a fast acting fuse immediately after J3 (power switch connector) and in the 5V regulated power supply. These fuses we subsequently removed from the design.
© 2014 – 2020 Rod Gatehouse AD5GH