Agilent Technologies 856290216 service manual Third Converter

Third Converter

Refer to function blocks A, B, C, D, and E on Al5 RF Section Schematic Diagram (sheet 4 of 4) in the HP 8560 E-Series Spectrum Analyzer Component Level Information.

The 3rd converter consists of the 2nd IF distribution, 2nd IF amplifier, double balanced mixer, 10.7 MHz bandpass filter, and flatness compensation amplifier. The 2nd IF distribution switches between two possible 2nd IF inputs: the internally generated 2nd IF, or the external mixing IF INPUT. A variable dc bias can ,be applied to the IF INPUT for external mixers which require such bias. The selected input is fed to the 2nd IF Amplifier. This amplifier consists of four stages of gain and two stages of SAW filters for image frequency rejection.

The flatness compensation amplifier consists of two fixed-gain stages and two stages of variable gain. This provides an overall adjustable gain of 4 dB to 30 dB. This gain is adjusted during an spectrum analyzer sweep to compensate for front-end conversion-loss versus frequency. Perform the following steps to test the amplifier gain:

The 10.7 MHz bandpass filter provides a broadband termination to the mixer while filtering out unwanted mixer products.

1.On the HP 85623, press (m), then 1X-83. MIXER .

2.In the 2nd IF distribution (function block A), diode CR802 should be forward biased and diode CR801 should be reverse biased.

3.Disconnect W35 (coax 92) and connect a signal source to A15J801. Set the source to the following settings:

Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310.7MHz Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -30 dBm

Caution	For troubleshooting, it is recommended that you use an active probe, such
	as an HP 85024A, and another spectrum analyzer. If an HP 1120A active
	probe is being used with a spectrum analyzer having dc coupled inputs, such
	as the HP 8566A/B, HP 8569A/B and the HP 8562A/B, either set the active
	probe for an ac-coupled output, or use a dc-blocking capacitor between the
	active probe and the spectrum analyzer input. Failure to do this can result in
	damage to the spectrum analyzer or the probe.

4.Use an active probe with another spectrum analyzer to measure the signal at A15TP601 (function block C). The signal should measure -17 dBm f4 dB confirming the operation of the 2nd IF Amplifier.

5.Use an active probe with another spectrum analyzer to measure the 300 MHz signal into the LO port of the third mixer. The signal should measure at least +20 dBm.

6.Measure the power of the mixer 10.7 MHz IF output. The signal level should be approximately -22 dBm.

7.Move the WR PROT/WR ENA jumper on the A2 controller assembly to the WR ENA position.

8.While measuring the 10.7 MHz IF output signal at the mixer, adjust the signal source until the level of the 10.7 MHz IF is -40 dBm.

RF Section 12-17