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53D181F450JT6_Datasheet PDF

来源:LM317 Electronics Components编辑:SolaHD时间:2021-06-15 15:37:48

Frequency error causes the group delay response of the spectrum analyzer filters to be offset on the trace, which does not present a problem if only the flatness is of interest. However if the frequency stability of the converter LO is poor then this offset will drift up and down, which causes more difficulty. Although auto scaling may help in this case, the only real solution is to stabilize the converter LO. The magnitude of this effect has been measured as typically 0.1 ns change in group delay per 1 kHz frequency error.

Testing group delay flatness on a test bench is fine for components that are relatively portable, but there are many instances where the device under test does not lend itself to this approach. A particular example is when the DUT is a complete satellite link, which clearly cannot be measured by a single instrument in a test lab. There are many reasons why satellite in-orbit testing needs to be carried out. It is generally performed following launch and prior to the release of the satellite to the customer, to verify the integrity of the communications payload and the antenna platform. Regular checks may also be carried out in service for the purpose of verifying performance or resolving anomalies.

53D181F450JT6_Datasheet PDF

Group delay over frequency, especially through frequency conversion, has proved a particularly difficult parameter to measure for satellite links. Figure 4 shows linear and parabolic group delays, which are typical of the types of delay experienced in satellite networks. Parabolic delay is usually associated with bandpass filters found in satellite transponders and communication equipment.

The sinusoidal delays are often caused by impedance mismatches in the system. Ideally, the group delay should be flat – a straight line with no slope – so that all frequencies across the carrier bandwidth experience the same time lag through the link. If this is not achieved then there will be interference between the recovered digits, making them difficult to discriminate between and thus causing errors.

Measurement system

53D181F450JT6_Datasheet PDF

The Aeroflex satellite group delay test system uses two microwave system analyzers fitted with the Group Delay Option 22, coupled with a control PC and serial modems running dedicated software to obtain a relative group delay measurement across the entire link. The test system is configured to generate the test signal to be applied to the uplink, and to analyze the transponded signal received at the downlink to obtain the group delay variation and to perform in-band gain flatness measurements. The two systems are synchronized together across the frequency sweep.

The system can be used for the measurement of group delay and other transfer characteristics of satellite links from ground stations, either colocated or remote, through the in-orbit transponder. A set-up screen enables the selection of the input, output and/or conversion frequencies and levels.

53D181F450JT6_Datasheet PDF

Transit time

The transit time to and from a satellite can be considerable, even for one that is in low earth orbit. For a geostationary satellite it is typically around 250 ms. Because the source and receiver frequencies are synchronized, this can mean in practice that the receiver, which will have an aperture of around 1 MHz, will have moved beyond the received signal, making it necessary to further offset the source and receiver frequencies to compensate for the transit time.

Phase 2: Deploy a component The objective of the component deployment phase is to test and refine the new capabilities put in place by developing a single component with Model-Based Design while limiting the exposure. The generated code is treated as hand-code and manually integrated with standard production application build for the purposes of this phase. Learning from this phase of the process and refinements are fed back into the migration plan as process improvements.

Phase 3: Deploy the full application The objective of the full application deployment phase is to develop a full application using Model-Based Design, generating code, and automatically building and downloading the executable onto the target. The integration process with basic software (operating system, device drivers, and communication stacks), as well as the build and download processes are fully automated.

Phase 4: Optimize and expand rollo ut The objective of the expanded rollout phase is to optimize and deploy the process to the wider organization. The lessons learned from the previous phases are factored into the process in preparation for deployment. Activities in this phase focus on process improvements to address the wider organizations needs and further improve the process capability and maturity in areas such as requirements traceability, automated document generation, and more extensive use of plant models for continuous verification.

Choose the appropriate legacy components for migration Many production organizations have significant amount of legacy code. Should all of the legacy code be converted to models? If so, should this be outsourced or done in house? How much effort would be involved and what would be the benefits?

As discussed in Best Practices for Establishing a Model-Based Design Culture” [Ref. 1], migration represents a tremendous learning opportunity. It’s not uncommon for an embedded control strategy developed over the years by different authors to have sections that are not well understood by the current designers. The process of modeling the existing algorithm allows the designer to get a deeper understanding of these areas while improving clarity, quality, and maintainability.

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