Agilent Technologies E8257C PSG, E8267C PSG, E8247C PSG CW Signal Loss While Working with a Mixer

Troubleshooting

RF Output Power Problems

Signal Loss While Working with a Mixer

If you experience signal loss at the signal generator’s RF output during low-amplitude coupled operation with a mixer, you can solve the problem by adding attenuation and increasing the RF output amplitude of the signal generator.

Figure 10-1 on page 190 shows a hypothetical configuration in which the signal generator provides a low amplitude signal to a mixer.

Figure 10-1	Effects of Reverse Power on ALC
	SIGNAL GENERATOR
	OUTPUT CONTROL
		ALC LEVEL	RF OUTPUT	MIXER
		= - 8 dBm	= - 8 dBm
	RF LEVEL			LO
	CONTROL
	DETECTOR	DETECTOR	LO FEEDTHRU	LO LEVEL
	MEASURES	MEASURES	= - 5 dBm	= +10 dBm
	- 8 dBm	- 5 dBm
	ALC LEVEL	REVERSE		IF
		POWER

The internally leveled signal generator RF output (and ALC level) is -8 dBm. The mixer is driven with an LO of +10 dBm and has an LO-to-RF isolation of 15 dB. The resulting LO feedthrough of -5 dBm enters the signal generator’s RF output connector and arrives at the internal detector.

Depending on frequency, it is possible for most of this LO feedthrough energy to enter the detector. Since the detector responds to its total input power regardless of frequency, this excess energy causes the ALC to reduce the RF output of the signal generator. In this example, the reverse power across the detector is actually greater than the ALC level, which may result in loss of signal at the RF output.

Figure 10-2 on page 191 shows a similar configuration with the addition of a 10 dB attenuator connected between the RF output of the signal generator and the input of the mixer. The signal generator’s ALC level is increased to +2 dBm and transmitted through a 10 dB attenuator to achieve the required -8 dBm amplitude at the mixer input.

190 Chapter 10