University engineering student clubs often find themselves with inactive members for lack of interesting design projects. I propose a variety of projects useful for the general public, for amateur radio and radar experimenters.
“ChildNet” child location tracking and alert system
A child-locator application using the latest SiRFStar-III chipsets and a low-power UHF (900MHz) data transceiver to be embedded into the child’s shoe.
The transceiver would only be powered on when the pressure switch embedded had experienced EITHER walking activity in the last hour, or a deviation from the upright position (child not standing, and the shoe is not at rest in an upright position).
The shoe would send a “danger” condition if the GPS detected child travel outside a geo-fenced area, or upon loss of the “heartbeat” signal sent at 0.1% of normal power level by the home transmitter. UHF antenna elements would exist at the toe and heel of the shoe to help ensure optimal transmission in a variety of shoe orientations.
A network of “ChildNet” transceivers could be installed on lampposts and cell phone towers to receive uniquely-identified shoe transmissions when the child had strayed too far from the home base to have direct data communications. SMS text could be sent to parents’ cell phones, or a handheld GPS Parent transceiver could be used in areas away from home, that set an automatic geo-fence centered on the Parent transceiver.
Using safe rechargeable batteries, a magnetic coupling charging mat that the shoes would be placed on each night would keep the ChildNet shoe safety system active with minimal user intervention. Dozens of children could use the ChildNet system on the same playground, and teachers could equip themselves with a Guardian transceiver that would send heartbeat pulses at 0.1% power, serving all the children on the playground with the ChildNet system in their shoes.
The first task to be accomplished is an experiment with a lossy dielectric brick on top of a SiRFStar-III GPS unit that is lying on the ground to see what lowest angle (e.g. 35 degrees) the GPS satellites can reliably (95%+) be received at in average terrain.
Then, a study should be run establishing what percent of the time at least 3 satellites are at or above that elevation.
Outboard Compandor for two-way radio
Inexpensive integrated circuits like the On Semiconductor SA572 allow compandored audio. Compandored audio increases the perceived SNR by greatly reducing audio gain for signals below a threshold, and greatly increasing gain for signals above that threshold. It would be of interest to amateur radio operators to have such a circuit for noisy HF SSB.
A circuit should be constructed allowing amateur radio operators to connect this unit inline with their existing microphones, and also explore making a version small enough to embed in the handheld microphones.
The project suggested is one that could potentially benefit any amateur radio operator using analog voice communications. The idea is to use a compandor IC such as used in commercial two-way radio to improve the signal to noise ratio of ham radio analog voice communications, whether AM/FM/SSB. The circuit intelligently and aggressively compresses transmitted audio, in a “better” fashion than the simpler clipping circuits commonly used in ham radio.
The circuit also has the capacity to “expand” the receive audio when the transmitting station is transmitting “compressed” audio. This provides a further S/N boost.
The apparent S/N increase is said to be on the order of 20 dB. Note that this apparent increase is caused by increasing the average power of the transmission; peak power is still limited by the radio. You don’t need to have this circuit on both ends to get the improvement, though greater improvement is provided when the circuit is on both ends.
Once the circuit is proven to work, a surface-mount version could be created that would fit inside mobile radios and the speaker-microphone of hand-held radios.
The compandor IC I’m thinking of is the SA572NG, available from Mouser for $6.83. It needs a few common resistors and capacitors external to the IC as well.
Digital “back-end” for high performance radio transceivers
Initial trial would take a low-cost yet high-performing architecture (Elecraft K2) and bypass the analog demodulator/modulator, instead using a National Instruments DAC and Labview to create an IF software suite. The theoretical gains modeled in Matlab could then be experimentally tested.
The next stage is development of a black-box that will attach into the host radio’s TX & RX IF, perhaps using the Analog Devices Blackfin (e.g. ADSP-BF523) series. A more advanced prototype would be configurable to send/receive CAT commands with the specific transceiver to achieve transparent operations. For example, the host transceiver is commanded by the user to change from FM to SSB. The host transceiver will set its synthesizer to the appropriate offsets, and select an internal filter best matched to the requested bandwidth. The high-dynamic range ADC in the black-box will feed the Blackfin with the best quality signal that the host transceiver can achieve. Likewise, a wide range of new transmit waveforms will be possible with the Blackfin in control.
The final product could be made nearly transceiver-agnostic, assuming the transceiver IF frequency is within the DAC capabilities (and down/up-converted if it’s not). An end-user calibration to their specific transceiver would allow pre-distortion profiles to be created, allowing maximum efficiency through time-efficient use of maximum possible bandwidth, whether the host is a vacuum-tube transceiver or of a more modern architecture.
iPod “Power Booster”
Students can rock their dorm and build their own inexpensive powered speakers by using a high-gain audio IC like the TA7222.
10 meter PropNet
Look into modifying CB radios to work in the data portion of the 10 meter band for PropNet.