Enclosures

__**Enclosures**__

The project itself is split between three separate enclosures. The first enclosure houses the RF frontend and the power board and in the second enclosure the ADC and FPGA. The third box contains an audio mixer board which is used for system testing to ensure the RF front end is working properly. There are several terminals and connectors on each of the enclosures.

RF Frontend and Power Board Enclosure
 The box chosen for this enclosure was a prefabricated unpainted aluminum case from Hammond Manufacturing, specifically the J-884 PL/UNPD which separates into two U-shaped pieces. The two pieces of the enclosure slide into each other and lock into place when the rivets of the top half pop into the holes of bottom half. The box can quickly be opened up by simply applying pressure to both sides of the box and removing the top half.

On the front face of the enclosure there are two banana plugs which can be used to power the system with a DC source such as a battery or benchtop power supply. The color of each plug represents the expected polarity; Red for positive and black for negative. There is also a 2.1mm DC power jack which can be used to power the system from a wall transformer. To properly power the system, a voltage of 13V – 20V is expected with the capacity to deliver 1.5A of current. Also on the front face of the enclosure just above the power terminals is a three position switch which can be used to select the power source or turn the system off entirely. The left most position of the switch selects the wall transformer supply while the right most position selects the banana plug terminals. The middle position of the neutral position where neither side is selected. On the back face of the enclosure is also another 2.1mm DC power jack which is used to power the ADC in the second enclosure.

There are also two female, panel mounted, BNC connectors on the RF frontend and power board enclosure. The BNC connector on the front panel is designated for the antenna input while the BNC connector on the back panel is used to connect the RF front end to the ADC.

The board assembly is supported and mounted to the enclosure using aluminum standoffs which electrically ground both the RF frontend and the power board to the aluminum enclosure. The aluminum case helps to shield the sensitive RF frontend from outside sources of RF radiation as well as act as an excellent heatsink. Rubber feet on the bottom of the enclosure ensure that there is clearance between the bottom of the box and what ever it may be resting on. This is particularly important if it is placed on anything metallic which may have a ground at a different reference level, as this may reduce the performance of the RF front end or even potentially damage the sensitive analog components.

ADC and FPGA Enclosure
 The enclosure chosen to house the ADC and FPGA is the 1415F produced by Hammond Manufacturing. This relatively large enclosure is made of 18 gauge steel and has two end panels which can be removed by unscrewing six screws from each panel. This particular enclosure was chosen because of the unique ADC and FPGA board assembly which requires a larger area to mount the boards.

This enclosure only has two external panel mounted connectors, where one of the connectors is for the input signal from the RF frontend and the other connector is a 2.1mm DC power jack used to power the ADC. Both the ADC and FPGA are mounted to the enclosure using nylon standoffs which ensure that neither the ADC’s nor the FPGA’s ground references are electrically connected to the case.

One of the reasons a multiple enclosure scheme was utilized was for modular testing purposes (the RF frontend and power board could easily be tested separate from the ADC and FPGA), and to keep the RF ground, Analog ground, and Digital ground separate to reduce the amount of noise fed to the digital side of the project which could drastically effect the performance of the ADC.

Audio Mixer Enclosure
 The enclosure chosen for the audio mixer is a small aluminum project box purchased from RadioShack. The mixer printed circuit board is just the right size for this enclosure. There are two access holes drilled into the front face and side of the box. On the front face of the box is a 2.1mm DC power jack and on the side of the box there is an SMA connector extends out from the box. The audio mixer is only used to test the operation of the RF frontend and as such, the ADC and FPGA will not be connected to either power or signal out. Instead, the audio mixer is powered from the barrel jack on the RF frontend and the output signal from the RF frontend is connected to the mixer circuit.

Opposite the DC power jack is a 3.5mm male stereo cable. This cable can be connected to the microphone jack on the personal computer and with a single command in the terminal window, enable the audio from the stereo jack to be played through the computers internal or external speakers. Alternatively, a female to female adaptor cable may be used if headphones are the preferred method of playing the mixer audio.