This delay is made up of several components—some of which the RTG system can control, some of which it cannot—Total Delay = System Minimum Delay + Digital Delay. The following figure shows the different contributions of delay.

System Minimum Delay—The minimum delay is achieved by setting the digital delay to 0. Minimum delay is the sum of the External Delay and the System Delay.

• External Delay—Any delay outside of the RTG system (from cabling, over-the-air, and so on). External delay is the sum of the delay from the radar to the RTG and from the RTG back to the radar. The RTG system does not have a way to measure this delay. The user must determine what this delay is and inform the RTG of this value.
• System Delay—The RTG system acquires and generates an RF signal and performs DSP algorithms for signal quality (equalization and LO reduction). This process takes a finite amount of time. Exactly how much time is required can vary based on system settings. The RTG provides a system self-calibration to calculate this value.

Digital Delay—The RTG system creates programmatic delay for up to four targets. This provides a resolution of 800 ps for the PXIe-5830/5831/5832/5841 or 400 ps for the PXIe-5842. The digital delay is applied differently based on personality, as shown in the following figure.

Table 2. Digital Delay

Pulse Aware	Pulse Invariant

• Common Delay (Pulse Invariant personality only)—This single block is shared by all targets.
• Target-Specific Delay—Each target has its own delay block. This block is capable of extending the common delay up to the maximum range window.
  Note The Pulse Invariant personality requires that the difference in delay between all four targets must be within 52.4 µs (for the PXIe-5830/58318/32/5841 VSTs) or 26.2 µs (for the PXIe-5842 VST) of each other. As depicted above, the RTG uses a common delay block to position the four possible targets at the beginning of the maximum range window. The target specific delays do not support these long delays and can only provide delays up to the supported delay setting value. Since every target must share the common delay, this limits how far apart in time all four targets can be for a given configuration. The maximum range window is therefore 52.4 µs or 26.2 µs. This means that the time difference in the delay between the closest and furthest targets must be less than or equal to this value.