Ground Sphere CubeSat Ground Station

h1. Ground Sphere Prototype Assembly Instructions v0.1 (OUTDATED)

{{toc}}

h2. Introduction

Version 0.2 is the second prototype, which sacrifices some of the flexibility of v0.1 in order to move toward a more polished kit version of the ground station. The overall design is the same between v0.1 and v0.2, but the details and several components have changed. Below are the assembly instructions for v0.2.

h2. The Antenna Base

The first component to build is the antenna base.  It is made from plumbing components available at any large hardware store.   The diameter and length of the pipe was chosen to allow the preamp to fit inside the base to electrically shield the preamp and give the antenna a weighted base for stability.  The use of a pipe thread to PVC adapter as a Coupler (ANT04) allows the antenna body to press fit into the base, making the antenna easy to assemble, disassemble, and tune.

# Cut a 3” section of 1 ¼” galvanized pipe to fabricate the Preamp Shield (ANT02) making sure to include the threads in component

# Screw the Weighted Base (ANT03) onto Preamp Shield (ANT02). 

# Screw the Coupler (ANT04) onto the Preamp Shield (ANT02) 

h2. The Ground Plane

The Ground Plane is sizes using the dimensions in the "GScalc spreadsheet available here":http://opendesignengine.net/dmsf_files/271?download=. 

# Cut out round pieces of conductive fabric (ANT14) and cotton muslin (ANT15) 7” in diameter

# Cut out with a 1” diameter hole in the center of the fabric disks (ANT14 and ANT15)  

# Quilt fabric discs together using conductive thread (ANT18).  Ensure all of the quilting threads end at common location near the center opening of the ground plane so that this may be connected to the ground line  

# Attach a small gauge ring terminal (ANT09) to the quilting threads with about 2” of slack between the top of the ground plane and the crimp

# Sew 6 small pockets on the muslin side of the Ground Plane to create the ground plane strut sleeves (ANT16); the pockets should extend from the center of the ground plane disk directly to the outer edge at 45 degree intervals like spokes on a wheel

# Fabricate the ground plane supports (ANT17)

## Cut 6 sections of 1/8" steel rod into 3" lengths  

## Bend the 6 sections of 18" steel rod to 90 degree angles 2" from one end

# Insert the long side of the Ground Plane Supports (ANT17) into the 6 ground plane strut sleeves (ANT16) on the bottom of the ground plane assembly 

h2. The Antenna Body

The Antenna Body is made from a 6" long section of 1" PVC electrical conduit.

# Cut a 6" long section of 1" PVC electrical conduit and debur it to form the antenna body (ANT01);  

# Test fit the Antenna Body (ANT01) into the non-threaded portion of the Coupler (ANT04); ensure it fits fully and snugly  

# Temporarily place the ground plane assembly on the antenna body so the support struts (ANT16) are flush against Antenna Body (ANT01) and the Coupler (ANT04). 

# Attach the Aerial Terminals (ANT06)

## Take one of the Aerial Terminals (ANT06) and position it so that the mounting hole is toward the ground plane assembly with the long portion in line with the Antenna Body (ANT01).  

## Adjust the distance from the top (screw side) of the Aerial Terminal (ANT06) to the top of the Ground Plane assembly so that it matches the D Plane figure in the "GScalc spreadsheet":http://opendesignengine.net/dmsf_files/271?download=  

## Mark the position of the Aerial Terminal (ANT06) on the Antenna Body (ANT01).

## Draw a line around the Antenna Body (ANT01) at the position of the first Aerial Terminal (ANT06)  

## Along this line mark 3 additional positions 90 degrees apart starting at the first Aerial Terminal (ANT06) mark.  

## Drill a 3/16” hole in each of the 4 position (a drill press is recommended)

## Drill another 3/16” hole ½” below one of the mounting holes from the previous step.  This will be for the RF line (coax) to exit the Antenna Body (ANT01) and connect to the Aerial Terminals (ANT06)

## Attach the Aerial Terminals (ANT06) at each of the first four holes with #10 nut and bolt (ANT07, ANT08) hand tight.  Note - these are temporary connections as these bolts are used for electrical connections in future steps 

# Place the End Cap (ANT05) on top of the Antenna Body (ANT01), but do not secure it with pipe cement or any other adhesive

h2. Antenna Line

# Fabricate the Antenna Line (ANT11) by cuttin an arbitrary length of 50 ohm coax cable; Note - the Antenna Line should be long enough to go all the way around the antenna body, down the hole drilled for it, and out the bottom of the antenna body with 3” to spare

# Carefully strip back 2” of the outer cladding of the coaxial cable and gently pull it free without damaging the braided shield below.  

# Gently push the braided shield back along the coax cable toward the insulation.  This will gather and expand the braid like a Chinese finger trap; allow it to expand.  

# Gently widen a gap in the side of the braid near the insulation and fish the center conductor out this hole with a fine screwdriver or dental pick, taking care not to unbraid the braided shield or breaking wires unnecessarily.  Inevitably one or two may break, but this is okay.  

# Gently pull the braid from the end in order to collapse it back down... help it a bit by smoothing it with your fingers.  

# Gently remove any broken wires from the braid.  Once thin and smooth, you may wish to place the section of coax insulation you previously removed over the exposed coax braid.  Without the center conductor in the braid, the insulation will slide over the braid easily protecting and insulating the ground from inadvertent contact.  

# Strip back about ¼” from the end of the center conductor and crimp a ring terminal (ANT09) on it.  Use the smallest wire rating for this ring terminal that will accept #10 hardware (red jacket).  You may wish to put a small loop in the end of the exposed wire before inserting it into the ring terminal in order to give the crimp more to hold on to.  

# Crimp a second ring terminal (ANT09) to the ground side.  For this you will need a larger lug (yellow jacket).  

# Slide the ground plane assembly over the bottom of the antenna body with the conductive fabric side up and the struts on the bottom.  

# Thread the unstripped side of the coax through the lower hole in the antenna body from the outside to the inside of the antenna body (ANT01), leaving ½” or so and the stripped and crimped ends hang out of the hole.  

# Mount the Coupler (ANT04) on the Antenna Body (ANT01).  Secure these parts with PVC cement if you wish. 

# Strip ½” of insulation from the coax and unbraid the shield from the coax hanging out the bottom of the Coupler (ANT04)  

# Gather the shield on either side of the center conductor and twist to form two ground leads.  

# Strip the center conductor back about ¼" to 3/16”, ensuring that the center conductor has enough insulation to prevent the ground wires from making contact with some margin.  

# Solder the center conductor to the input side of the preamp (RAD02) and the ground leads to the ground shield on either side of the input line on the PC board

h2. Phasing Loop

# Cut a section of 90ohm cable to a little over 2 ¾” in length to make the Phasing Loop (ANT12); Note - the math comes to 2.77456 or about 2 199/256”, but don’t sweat the accuracy... just measure 2 ¾” precisely and add the width of an Xacto knife blade.  The more accurately you can make this cut, the higher gain the antenna will have at the desired frequency.

# Strip the cable ¾” back on both ends and push the insulation back and fish the center conductor out as you did before on the RF line.  

# Strip back about ¼” from the end of the center conductor on each end and crimp ring terminals (ANT09) on the ends.  Use the smallest wire rating for this ring terminal that will accept #10 hardware (red jacket).  You may wish to put a small loop in the end of the exposed wire before inserting it into the ring terminal in order to give the crimp more to hold on to.  

# Crimp larger ring terminals (yellow jacket) to the ground braids.

h2. Preamp Line

# Fabricate Preamp Line (ANT12) by take the antenna assembly which came with the SDR (RAD01) and cutting it close to the antenna 

# Take the cut end (not the side of the cable terminated with the MCX connector) and strip ½” of insulation from the coax and unbraid the shield.  

# Gather the shield on either side of the center conductor and twist to form two ground leads.  

# Strip the center conductor back about ¼" to 3/16”, ensuring that the center conductor has enough insulation to prevent the ground wires from making contact with some margin.  

# Solder the center conductor to the output side of the preamp (RAD02) and the ground leads to the ground shield on either side of the output line on the PC board.

h2. Preamp Power Connector

# Fabricate the power jack (RAD03), by soldering the red lead to the input side of the preamp (RAD02) voltage regulator to a pre-wired barrel connector .  This can be best accomplished by soldering it to the pad labeled L5 on the side closest to IC1, the voltage regulator.  

# Solder the black lead to the ground shield at a convenient point around the outside of the preamp (RAD02) PCB.

This connection scheme will allow any standard power supply with a center positive barrel connector to be used, as the regulator can handle any voltage from 6V to 18VDC.  In a pinch, the power supply can be connected directly to the preamp PCB (RAD02).  The expected current draw of the preamp is around 35mA, so a good value for a fuse would be 1/4A, though most “wall wart” power supplies rated at 100mA will fail before then, so there is little point in putting a fuse inline, but plenty of reasons to double check your work.

h2. Assembly

# Remove the hardware (ANT07, ANT08) connecting the four Aerial Terminals (ANT06) to the Antenna Body (ANT01).  

# As you look at the antenna body with the top up and the hole where the wire exits facing you, arrange the antenna line (ANT11) coax so that the ground shield goes to the right and the center conductor to the left.  These are somewhat arbitrary, but it is necessary to know where things are in order to connect the phasing loop correctly.  

# Connect the ground of the antenna line (ANT11), the ground of the ground plane assembly (the conductive thread pigtail), and the ground of one of the ends of the phasing loop together by stacking the ring terminals on the #10 screw (ANT07).  Ensure the antenna line connector angles toward the antenna line hole in the antenna body, the ground plane ground goes straight down, and the phasing loop’s angles away from the antenna line hole.  

# Place the ground lug (ANT06) on the screw (ANT07) last with the screw terminal at the top

# Insert the screw into the hole in the antenna body (ANT01) on the right side as viewed with the antenna line hole facing you.  

# Tighten the screw securely with a nut (ANT08) on the inside of the antenna body making sure the ground lug (ANT06) remains in line with the axis of the antenna body (ANT01) and the ring terminals (ANT09) do not rotate causing strain on the wire crimp connections.

# Do the same with the center conductor on the antenna line (ANT11) and the center conductor from the same side as the ground used in the previous steps on the phasing loop (ANT13) bolting them and another ground lug (ANT06) to the hole on the left of the antenna body (ANT01) when viewed with the antenna line hole facing you.  What this should look like is the antenna line (ANT11) conductors straddle the antenna body (ANT01) on one side, while the phasing loop (ANT13) conductors straddle the antenna body (ANT01) on the other.

# Rotate the antenna body 180 degrees so that the antenna line hole in the antenna body (ANT01) is facing away from you

# Take the phasing loop (ANT13) and gently turn it to the right wrapping it around the antenna body (ANT01).  Heating it a little with a heat gun or placing the assembly in sunshine may help it the phasing loop proves to be stiff.  

# Connect the ground wire on the phasing loop (ANT13) to the ground lug (ANT06) directly above the antenna line hole and the center conductor to the ground lug (ANT06) in the remaining hole 180 degrees opposite of the antenna line’s exit hole.  Tighten as before, making sure the ground lug remains in line with the axis of the antenna body (ANT01) and the ring terminals (ANT09) do not rotate causing strain on the wire crimp connections. 

h2. Fabricating and Installing the Aerials

Note, in the "GScalc spreadsheet":http://opendesignengine.net/dmsf_files/271?download= the aerials (ANT10) are defined as loops 13.71 inches long.   

# Cut two pieces of romex house wiring, leaving at least one piece insulated, to a length of 14 ¼”.  

# Strip off ¼” of insulation on both ends of the insulated arial(s).  

# Position a pair of pliers to grip on the bare wire directly against the insulation, and bend the end 90 degrees.  Do the same for the other end, taking care to bent them in the same direction.  To be clear: If the wire is placed on the ground with one stripped end pointing up, the other would be pointing upward also.  

# Repeat this process with the second aerial.

# Take one of the aerials between thumb and forefinger clamping with a bit of pressure and pull it through with your other hand in order to curve the wire, As you do so, ensure that the stripped ends end up on the outside of the curve.  To be clear:  when the wire comes full circle, so that the ends touched, the stripped ends point away from the center of the circle. 

# Repeat this process with the second aerial taking care with both to form a smooth arc.

# Partially unscrew the set screws from the Aerial Terminals (ANT06) on the side of the antenna body (not the ground lug mounting screws).  Insert the loops into opposite ground lugs and tighten, taking care not to torque the lugs off true.  A large amount of torque is not required.  If the Aerial Terminals are numbered 1 thru 4, one loop would connect 1 and 3, while the other would connect 2 and 4.  

# Once tightened, arrange the loops to be circular and when viewed from the top, cross at the center of the antenna body (ANT01) and at right angles.

h2. Installation and Testing

# Secure the ground plane struts (ANT17) to the antenna body (ANT01) with a zip tie or two, making sure the ends are in contact with the Coupler (ANT04) under them and are in line with the antenna body (ANT01).  

# Arrange the struts to make the ground plane as flat as possible.  

# Thread the preamp output line (ANT12) and preamp (RAD02) through the steel pipe and pipe flange base.  

# Without torquing the preamp, thread the base on the antenna body.  At this point you may wish to cover the preamp with electrical tape or heat shrink tubing to insulate it, but any part of the preamp PCB that can touch the sides of the pipe should be a ground anyway.  

# Gently push the preamp assembly into the base of the pipe.  

# Place some rubber or felt feet on the base of the antenna base (ANT03) to keep from scratching paint or furniture.  

# Plug the amplifier (RAD02) into a 12VDC source.  Current draw should measure about 35mA +/-5mA.  If not, inspect the unit for damage or poor solder connections.  

# Connect the MCX connector on the preamp line (ANT12) to the SDR dongle (RAD01) and tune the SDR software to 900 MHz.  

# Using a cordless phone or other 900 MHz source verify that the antenna is receiving and amplifying signals.  Further testing of the preamp (RAD02) is out of the scope of the average hobbyist.

Tuning the antenna is a trial and error process, adjusting the length of the aerials (ANT10), phasing loop (ANT013), and distance between the aerials and the ground plane assembly by adjusting the position of the ground plane struts.  Remember that larger components and dimensions tune for lower frequencies and smaller components and dimensions tune higher frequencies.  Tweaking and replacing parts while observing the effects will allow you to tune the antenna and align your GroundSphere satellite ground station to peak performance.