Although lentil is a valuable source of protein in human diet, and its straw is a highly valued animal feed, its production in West Asia and North Africa is limited, mainly due to problems associated with harvesting. Mechanical harvesting has not been successful because: 1)Seed and leaf shattering occurs when plants are mature; 2) low cutting heights are required since lentils tend to be short (only 20-30 cm tall) with pods borne close to the ground; 3) lentils are usually grown in marginal stony fields where stones cause damage to essential parts of harvesters; and 4) uneven ripening. Hand harvesting cause minimal losses, but it is labor intensive and labor is becoming increasingly scarce.--The objective of this study was to design and test a prototype lentil harvester for small farms with focus on the cutting/feeding mechanism. A hand held preliminary system was first designed and tested and the results were then used to develop a self-propelled prototype, which cuts and collects whole plants without threshing. Very low (5 cm average) and clean cut with negligible seed and leaf losses were achieved under various field conditions (stony, weedy and weeded), wide range of plant moisture (54.7% to 8.7% wet basis) and operation speeds (up to maximum design speed of 4 Km/h). The results were superior to combine and forage harvesters while comparable to--typical hand harvesting (hand pulling). Nevertheless, the ability of the prototype to harvest very dry crop with minimal losses allows farmers to delay harvest until most of the lentils is mature, thus overcoming the the problem of uneven maturity.
--The objective of this study was to design and test a prototype lentil harvester for small farms with focus on the cutting/feeding mechanism.
Radio frequency power amplifiers (PAs) are the most challenging part of the design of radio systems since they dictate the overall system's performance in terms of power efficiency and distortion generation. The performance is further challenged by modern modulation schemes which are characterized by highly varying signal envelopes. In order to meet the spectrum mask requirements, PAs are usually operated at high power back-off to ensure linearity, at the cost of efficiency. To tackle this issue, many efficiency enhancement techniques have been presented in the literature. In fact, these techniques do increase the PA power efficiency at back-off, however, efficiency enhancement techniques do not ensure the linearity of the PA. Furthermore, these techniques may lead to additional distortion. On the other hand, several linearization techniques have been developed to mitigate the PA nonlinearity problem and allow the PA to operate at less back-off. Digital Pre-Distortion (DPD) technique is gaining more attention, as compared to other linearization techniques, thanks to its simple concept and advancements in digital signal processors (DSP) and signal converters. DPD technique consists of introducing a nonlinear function before the PA so that the overall cascaded system behaves linearly. It was clear from the literature that this technique showed good performance. Yet, it has primarily been validated using commercial test equipment, which has good capabilities, and far from the real world environment in which this technique would be implemented. Indeed, DPDs would need to be implemented in signal processors characterised by limited resources and computational accuracy. This thesis presents an implementation of several DPD models, namely look-up table (LUT), memoryless polynomial and memory polynomial (MP), on a field programmable gate array (FPGA).
Radio frequency power amplifiers (PAs) are the most challenging part of the design of radio systems since they dictate the overall system's performance in terms of power efficiency and distortion generation.
