3.Check for excessive LO feedthrough. Use the LO Feedthrough performance test in the Installation and Verification Manual, but check over a Center Frequency range of 300 kHz to 100 MHz. The LO Feedthrough will be 3.9107 GHz greater than the Center Frequency setting.

Harmonic/Spurious Outputs Too High

Harmonic and spurious outputs may be generated by A10 itself or may be present on the either the 600 MHz drive or 1st LO drive signal. There is a direct relationship between spurious signals on the 1st LO and spurious signals on the TG output. There is a five-to-one relationship between spurious signals on the 600 MHz drive and the spurious signals on the TG output. For example, if the 600 MHz signal moves 1 MHz, the TG output signal will move 5 MHz. This is due to the multiplication in the pentupler.

1.If the Harmonic Spurious Responses performance test failed, connect another spectrum analyzer, such as an HP 8566A/B, to the HP 8560A 1ST LO OUTPUT connector. Set the HP 8560A to each frequency as indicated in the performance test, with the Span set to

0 Hz. At each frequency setting,press [m],(K), MORE 1 OF 2, FREQ DIAGNOSE, LO FREQ . The frequency displayed will be the fundamental frequency of the 1ST LO

OUTPUT. Use the HP 8566A/B to measure the level of the second and third harmonics of the 1st LO signal.

Note

The 1st LO typically has a higher harmonic content than the tracking

 

generator output. For the purposes of this check, it is the variation in

 

harmonic content versus frequency which is important.

 

 

If the variation of the harmonic level of the 1st LO versus frequency tracks the harmonic level variation of the tracking generator output, repeat this step while measuring the 1st LO signal at the end of W43 nearest AlO. If there is little variation in the 1st LO harmonic level between the 1ST LO OUTPUT connector and W43, and the relative variation in harmonic level tracks with the TG output harmonic level, suspect either the A7 LODA or A11 YTO.

If the harmonic level variation of the 1st LO versus frequency does not track the harmonic level variation of the TG output, suspect AlO.

2.If sidebands are present at the same frequency offset at every output frequency, check the spectral purity of the 1st LO and the 600 MHz drive signals using another spectrum analyzer. When checking the 1st LO, the HP 8560A must be set to zero span. Press ICAL), MORE I OF 2, FREQ DIAGNOSE, LO FREQ to determine the 1st LO frequency. A 1 MHz sideband on the 1st LO will appear as a 1 MHz sideband on the output signal.

To verify that the 600 MHz drive or 1st LO signal is responsible for the sidebands, substitute a clean signal for the 600 MHz drive or 1st LO signal. If the sidebands on the output disappear when using the clean signal, the substituted signal was responsible for the sidebands.

Note

The 600 MHz drive signal should be -8 dBm+/-3.5 dB. The 1st LO signal

 

should be +16 dBm f2 dB.

 

 

11-22 RF Section