The Difference between DR3 and RMDR

In receiver performance, close-in 3rd order dynamic range and reciprocal mixing dynamic range are distinct metrics that characterize a receiver's ability to handle strong interfering signals while maintaining sensitivity to weaker desired signals. Here's a clear explanation of their differences:

Close-in 3rd Order Dynamic Range (DR3)

• Definition: This measures a receiver's ability to handle two strong interfering signals close in frequency to the desired signal without generating significant third-order intermodulation distortion (IMD3) products that could interfere with the desired signal.

• Key Aspects:

• Focuses on third-order intermodulation distortion caused by two strong signals (at frequencies f1 f_1 f1​ and f2 f_2 f2​) producing distortion products at 2f1−f2 2f_1 - f_2 2f1​−f2​ or 2f2−f1 2f_2 - f_1 2f2​−f1​, which may fall within or near the desired signal's frequency.

• "Close-in" refers to the interfering signals being relatively near the desired signal in the frequency spectrum (e.g., within a few kHz or tens of kHz).

• It is determined by the receiver's third-order intercept point (IP3) and its noise floor.

• Measured in dB, it represents the range between the minimum detectable signal (MDS, or noise floor) and the level at which IMD3 products become problematic.

• Formula: DR3=23(IP3−MDS)DR3 = \frac{2}{3} (IP3 - MDS)DR3=32​(IP3−MDS) where IP3 is the third-order intercept point (in dBm), and MDS is the minimum detectable signal level (in dBm).

• Practical Impact: A high close-in DR3 indicates the receiver can tolerate strong nearby signals without generating distortion that masks the desired signal. It’s critical in environments with strong adjacent signals, like in crowded radio bands.

Reciprocal Mixing Dynamic Range (RMDR)

• Definition: This measures a receiver's ability to reject strong interfering signals close to the desired signal frequency without the receiver's local oscillator (LO) phase noise mixing with the interferer to raise the noise floor in the desired signal’s frequency band.

• Key Aspects:

• Focuses on phase noise from the receiver’s local oscillator. When a strong interferer is present at a frequency offset from the desired signal, the LO’s phase noise can "mix" with the interferer, transferring noise into the desired signal’s bandwidth.

• The result is an elevated noise floor, which reduces the receiver’s sensitivity to weak signals.

• RMDR is also measured in dB and is defined as the difference between the level of a strong interferer and the equivalent noise floor increase caused by reciprocal mixing.

• It depends heavily on the phase noise performance of the receiver’s LO at specific frequency offsets (e.g., 2 kHz or 10 kHz from the carrier).

• Practical Impact: A high RMDR indicates a receiver with low phase noise, capable of maintaining sensitivity in the presence of strong nearby signals. It’s particularly important in scenarios like amateur radio or communications in dense signal environments.

KEY DIFFERENCES:

Summary

• Close-in 3rd Order Dynamic Range deals with distortion caused by nonlinearities in the receiver when handling two strong signals close to the desired frequency. It’s about managing intermodulation products.

• Reciprocal Mixing Dynamic Range addresses the degradation of receiver sensitivity due to the local oscillator’s phase noise mixing with a strong interferer, effectively raising the noise floor.

Both metrics are critical for assessing receiver performance in challenging RF environments, but they focus on different limitations: nonlinearity (DR3) versus oscillator phase noise (RMDR). For optimal performance, a receiver should have high values for both to handle strong interferers without losing sensitivity to weak signals.

Additional Info on RMDR:



Terms explained for Rob Sherwood's Table of Receiver Performance.