Spread Spectrum - Frequency Hopping Demonstrator

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• published: 08 Jan 2011
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This video (appologise for the quality - unedited) shows a quick lash up to test the concept of designing a Frequency Agile Spread Spectrum communication trainer for the No1 Radio School and the APO departments at DCAE Cosford. The setup shown in the video utilises some pre-used modules from other designs made in the department, but the overal purpose of the exercise was to bring something together so that we can demonstarte the potential to the instructional departments. The setup on the bench will provide the framework to build a prototype Transmitter and Receiversystem. Normally a system like this would require GPS or satelite means to ensure synchronisation. This wont be necessary in this particular development due to the requirement being for lab use and the proximity of the TX and RX units will be in the order of a few feet. Therefore synchronisation of the units will be via hardwired synchronization cables or maybe the use of 433MHz to serve as the medium. The reason for the slow hop, typically half a second, is to provide visability to the students who will be learning on this system, a fast hop would not show up so well on the spectrum analyser due to the sampling rate of the test equipment. Using direct digital synthesis (DDS) allows us to very much simplify the means of producing our local oscillator (LO) for the receiver and the master oscillator (MO) and more importantly, eliminating lock time if we had used traditional PLL technogy. The DDS can 'retune' pretty much in the time it takes to transfer a 32 bit frequency change word from a parallel bus (taken in 2 cycles plus a command instruction to update the frequency registers inside the DDS) which is typically tens of microseconds. Its early days yet but when this project is complete the aim is to then work on a direct sequence spread spectrum system, which I think will be a little more challenging.