Every development includes new features, problem resolution, manufacturing maturity, as well as surprising results. Development of the tri-band transmitter was no different.The complete control over the RF output power with independent control of the RF power going to the upper and lower antennas was evidently a useful tool for lab testing. No longer does the test engineer need to carry the variety of RF attenuators to match the RF levels driving the test equipment to perform BER tests.A simple commanded adjustment of the RF power allows for a smooth RF-level adjustment rather than the manual step attenuator, which eases performance testing. The author historically has not favored the 1-dB step adjustment in RF power. However, after completing this development, the advantage of such a feature is obvious, and the credit goes to the telemetry community for this advance.The ease of responding to both the 106-15 programming protocol and the 106-19 command protocol was a surprise. From a transmitter vendor's perspective, the transmitter command listing across the various versions of the IRIG standard has evolved to include well over 60 commands. For the user, having to remember the appropriate protocol for a given transmitter causes delays and inappropriate programming. The tri-band transmitter acknowledges the previous command structure as well as the latest IRIG standard command structure, which saves time and increases typing accuracy, for the test engineer.Throttling back the RF power to limit temperatures in the tri-band transmitter helps avoid hardware damage. In some applications, it's desirable for the transmitter to "die trying" and continue to transmit through high-temperature events. This isn't true for flight tests, though, when there are long pre-flight and flight times during which the temperature-limiting function will save the hardware from damage. This is certainly an advanced feature and welcomed by the flight-test community not to have to turn the transmitter off to cool down.Thumbwheel and serial-port programming is still required for these flight-test transmitters. The author found those features to be easy to use, presenting very few difficulties in communicating with the tri-band transmitter. The takeaway here is "the simpler, the better," and it all works. A friendly element of this type of interface is the "?" command, with which the test engineer can print out the many command structures for guidance in choosing the correct one.Cable-delay matching between the upper and lower antennas is quite easy using the STC balance displays on some of the vendor's receivers. The delay matching to within 1-bit time is required for STC demodulation performance as the interoperability testing results provided.As users gain experience using tri-band transmitters, requirements will continually evolve to assure successful reception of data in the current and future frequency bands.
展开▼
