TRF Noise Floor Related Question Prepared by Bill Wu

Objective This note is to address two questions about TRF3704 noise floor plot taken from a large span setting. Two cases all showed an elevated noise floor at the lower freq side of the carrier.

Summary A signal generator like E4438C could have a noisy far-out noise floor, which leads to the elevated noise floor at TRF3704 output. HP 8673E has a much cleaner far-out noise floor than E4438C. A BPF filter could be used to clean the dirty LO noise floor before sent to TRF3704 as LO source.

Case 1 Spectrum Plot SA noise floor, output w/ LO freq = 4, 5, and 6 GHz

Case 2 Spectrum Plot

LO Signal from Agilent Vector Signal Generator, from E4438C LO freq = 4 GHz LO freq = 5 GHz LO freq = 6 GHz

Observation Agilent E4438C showed a high noise floor at the lower freq range. The noise floor elevation becomes significant when the freq is large.

E4438C, 5.7 GHz signal filtered by a BPF, Freq = 5.3 GHz passing through a BPF (BW = 280 MHz) directly sent into Spectrum analyzer

Conclusion The 5.3 GHz BPF (280 MHz BW) removed the far-out noise at the lower side of the spectrum.

TRF3704 RF output using Agilent E44483C as LO, PLO=10 dBm, BB freq = 1 MHz LO freq = 4 GHz LO freq = 5 GHz LO freq = 6 GHz

Observation The RF output far-out noise of TRF was significant at the lower side of the RF freq using Agilent E4438C as LO. The output noise was more significant for the higher LO frequency.

RF Signal from Agilent Vector Signal Generator E4438C, Freq = 5.3 GHz LO passing through a BPF (BW = 280 MHz) LO directly sent into TRF370417

Conclusion The 5.3 GHz BPF (280 MHz BW) at the LO port cleaned the LO noise floor, which leads to a clean output noise floor of the TRF3704 RF output. High TRF3704 RF output noise was caused by the dirty LO far-out noise floor, not by the TRF3704 modulator.

TRF3704 RF output with LO from HP Signal Generator 8673E, PLO=10 dBm, BB freq = 1 MHz LO freq = 4 GHz LO freq = 5 GHz LO freq = 6 GHz

Observation HP Signal Generator 8673E has much clean far-out noise floor than Agilent E4438C.

RF output Signal using HP Signal Generator 8673E as the LO source, Freq = 5.3 GHz LO passing through a BPF (BW = 280 MHz) LO directly sent into TRF370417

Conclusion There is no need to use BPF to clean the LO noise floor if HP Signal Generator 8673E was used as the LO source.