Adding delay to a signal is instrumental in some applications, such as in signal propagation simulators and radar signal simulators. Delays can be implemented in a number of ways, including the use of precise lengths of semirigid coaxial cable. Colby Instruments, known for its trombone tuner for broadband delays (see Defense Electronics, p. S37), also offers compact delay modules based on switched PIN diodes. The firm's PDM series of programmable delay modules operate from 100 MHz to 3 GHz with delay steps from 1 to 2560 ps and delay resolution as fine as 1 ps, in compact housings measuring only 7.0 x 0.9 x 4.0 in.
The PDM series of PIN-diode delay modules (Fig. 1) consists of three models: the P1-PDM with delay steps of 1, 2, 4, and 8 ps (for a total delay range of 0 to 15 ps with 1-ps resolution), the P2-PDM with delay steps of 5, 10, 20, 40, 80, 160, 320, and 640 ps (for a total delay range of 0 to 1275 ps with 5-ps resolution), and the P3-PDM with delay steps of 1280 and 2560 ps (for a total delay range of 0 to 3840 ps with 1280-ps resolution). The total phase shift for the model P1-PDM is 5.4 deg. with resolution of 0.36 deg./GHz, while the total phase shift for the model P2-PDM is 459 deg. (with resolution of 1.8 deg./GHz) and the total phase shift for the model P3-PDM is 1382.4 deg. (resolution of 460.8 deg./GHz).
The absolute accuracy of the shortdelay model P1-PDM is 1 ps 0.5 ps, while the absolute accuracy of the P2-PDM is 1 percent per step 1 ps, and for the P3-PDM is 1 percent. All three of the delay modules are designed to handle input power levels to +25 dBm. They are programmed by means of TTL/CMOS control signals and require external power supplies of +12 and -12 VDC. The typical insertion loss for the model P1-PDM delay module is 2.47 dB at 0.5 GHz and 4.75 dB at 3 GHz when adjusted to the minimum delay setting; the insertion loss is only slightly higher at 2.49 dB at 0.5 GHz and 4.79 dB at 3 GHz when set at the maximum delay setting. The typical insertion loss for the P2-PDM delay module is 5 dB at 0.5 GHz and 9.9 dB at 3 GHz at the minimum delay setting, and 5 dB at 0.5 GHz and 10.6 dB at 3 GHz at the maximum delay setting. The typical insertion loss for the P3-PDM delay module is 1.33 dB at 0.5 GHz and 3.67 dB at 3 GHz at the minimum delay setting, and 5.34 dB at 3 GHz at the maximum delay.
The PDM-100A delay (Fig. 2) uses the PIN diode modules to achieve as much as 5.120-ns delay from 100 MHz to 3 GHz in an instrument housing. The resolution per step is as good as 1 ps, with accuracy of 1 ps. Both the instrument and the modules can be controlled by GPIB, Ethernet LAN, and RS-232C. The PDM-100A delay instrument can also be programmed remotely via the Internet using a Web browser to enter delay settings. Colby