Analog Power Busses Introduction


Stage Functionality

This stage of the build introduces the 12V, 5V, and 3.3V power busses for the analog "side" of the board. Since these busses are derived from the Softrock RXTX's 12V power feed, it is appropriate at this time to add the footers which provide communication between MOBO and Softrock boards.

The footers - installed to the bottomside of the board - provide the following connections:

The Softrock RXTX V6.3

The Softrock Lite + Xtal RXTX V6.3 must be built as documented in the WB5RVZ Enhanced Notes therefor, with the following exceptions:

It is always a good idea to double check the bill of materials in this set of documentation with the official BOM on the Mobo site. Discrepancies may be introduced inadvertently, as the changes are sometimes not communicated or discovered, making timely update of this site a problem.

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Analog Power Busses Schematic

(Click for Full Schematic)
Analog Power Bussesschematic


(above schematic has clickable areas that can be used for navigation)

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Analog Power Busses Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

11N5822 Shottky 3A diode1N5822Axial
1header, 2-pin Header
1header, 2-pin Header
2header, 2-pin RA Header
1header, 3-pin Header
1header, 4-pin Header
1header, 4-pin Header
1header, 5-pin Header
1header,right_angle, 3-pin Header
2header,right_angle, 3-pin Header
1misc hookup wireHookup
1shunt, 2-pin Shunt
40.1 uFSMT 0805
14.7 k ohm 5%SMT 0805 1/8W
20.1 uF(smt) black stripe (smt) black stripeSMT 1206
1header socket, female, 4-pin Socket
1header socket,female, 2 pin Socket
17805 voltage regulator7805 7805TO-220

Analog Power Busses Summary Build Notes

Analog Power Busses Detailed Build Notes

Bottom of the Board

Analog Power Busses Bottom View

Install Bottomside Rs, Cs, and Ics

C010.1 uFSMT 0805
C020.1 uFSMT 0805
C300.1 uFSMT 0805
R014.7 k ohm 5%SMT 0805 1/8W

Top of the Board

Analog Power Busses Top View

Install topside Rs and Cs

C240.1 uF(smt) black stripe (smt) black stripeSMT 1206
C250.1 uF(smt) black stripe (smt) black stripeSMT 1206
C430.1 uFSMT 0805
K01_Shuntshunt, 2-pin Shunt
Normal placement is on K1-1 and K1-2
K01header,right_angle, 3-pin Header
Normal operation: jumper across Pins 1 and 2

Install 5V Voltage Regulator

Install 5V Voltage Regulator photo
U017805 voltage regulator7805 7805TO-220

Prepare SR RXTX Board

This step prepares the RXTX board to accept the I2C bus lines and the PTT-I signal from the MOBO. It assumes you have already built the RXTX board (without the DIP switch or with the DIP switch removed) and with all of the jacks (J1-J4 installed.

Don't forget to remove the PIC (U6) from its socket on the RXTX before plugging in the MOBO - it is not needed when the MOBO is "in control". If concurrently building the RXTX V6.3, do not install the DIP switch and the PIC chip socket. If you have installed the PIC chip, you can just remove it from the socket and leave the socket there.

There is a jumper to select between +5V and +3v3 for pin 1 of the 4- pin header in the 2nd row under the DIP switch. Solder the jumper for +3v3.

The 6 footers of the Mobo mate with 6 corresponding female receptacles on the SR v6.3. Solder the receptacles with care to ensure they are perfectly perpendicular to the pcb. This will make it easier to have a perfect mating with the footers from the Mobo.

Use right angled header connectors for I/Q input and output pins, the +12V/GND power connector, and the ANT connector, as these connections have to emerge from underneath the Mobo.

One final modification to the RXTX V6.3 board is the replacement of the 1n4003 reverse polarity protection diode with a Schottky diode (3A current rating) or a !N5819 1A diode. This change will allow increased max RF power output from the Mobo, by at least 0.5W.

Prepare SR RXTX Board photo
Dxx1N5822 Shottky 3A diode1N5822Axial 
User-provided replacement fot RXTX V6.3's D1
P32_Mateheader socket,female, 2 pin Socket
Prepare the SR PTT_I/GND with mating female receptacle
P30_Mateheader socket, female, 4-pin Socket
Prepare the 2nd row under DIP of SR RFXTX to accept the 4 pin footer for I2C bus
JP1misc hookup wireHookup 
Install a pice of hookup wire at JP1 to provide 3.3Vdc to P30's pin 1.
ANTheader, 2-pin RA Header 
Recommended; Not supplied with kit
SR_PWRheader, 2-pin RA Header 
Recommended; Not supplied with kit
IQ_RXheader,right_angle, 3-pin Header 
Recommended; Not supplied with kit
IQ_TXheader,right_angle, 3-pin Header 
Recommended; Not supplied with kit

Install Board Interconnect Headers ("Footers")

This step installs the 6 sets of male header pins that serve as "footers" for the MOBO's connections to the SR RXTX. All of the footers are installed with their long pins protruding from the bottom of the MOBO board and their short pins soldered into the MOBO boards holes. Footer locations are shown in the graphic.

As an aid to getting correct footer alignment, plug each of the 6 male footers (P15, P17,K4, P19, P30, P32) into the corresponding female receptacles on the SR RXTX v6.3, using the SR as a "jig" to hold the pins in correct alignment for soldering. Then solder the footers onto the MOBO4.3 board while they are plugged into the SR receptacles.


Install Board Interconnect Headers (
P19header, 4-pin Header
J1 of SR (footer)
Connects to J1 on RXTX (S12V and QSE I and Q signals)
P15header, 5-pin Header
J2 of SR (footer)
Connects to J2 of SR RXTX V6.3
P17header, 2-pin Header
J3 of SR (footer)
Connects to RXTX J3 (Ant and Gnd)
K04header, 3-pin Header
J4 of SR (footer)
Connects to J4 of Softrock RXTX V6.3 (to QSD)
P30header, 4-pin Header
I2C connector (footer)
Footer to plug into 2nd row under DIP of SR RFXTX
P32header, 2-pin Header
Footer to plug into SR PTT_I
Prepare the SR PTT_I/GND with mating female receptacle

Analog Power Busses Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Analog Power Busses Testing

Voltage tests

Test Setup

Using your DMM and connecting the board to the RXTX V6.3, power up the RXTX V6.3

Measure the rail voltages (with respect to analog ground) at the testpoints indicated in the graphic below

Note (tx to Mike Collins, KF4BQ): If you happened to get around 0V on P32-1 wrt P32-2, you may have missed installing R01. That is the pullup on the PTT signal for the MOBO. If R01 is installed the voltage should be 3.6V: ((5V - Vbe)* 10K/14.7K)+.Vbe)

Voltage tests

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Pin 1 (rightmost pin) wrt Pin 2 (leftmost pin) of P32V dc~3.6tbd_______
Point A with respect to Point BV dc3.3tbd_______
Point C with Respect to Point DV dc5tbd_______
Point E with respect to Point FV dc12tbd_______
View RXTX V6.3 Specs for I2C bus connections View RXTX V6.3 RX Schematic with J3 and J4 View RXTX V6.3 TX Schematic and J1/P200 co9nnection view RXTX V6.3 TX Schematic with J2/P201 connection View RXTX V6.3 PTT Control stage builders notes