Wavetek 147 Especificaciones descargar pdf (Pagina 354)

Application Notes: Return Path Troubleshooting

330

down. The same thing can happen in customer installed passives unless

they have voltage blocking capacitors installed.

Troubleshooting CPD

• Pull a forward pad to see if the return "cleans-up". This is definitely CPD,

but very intrusive when doing this and may disrupt CPD temporarily.

• Try not to disturb anything in this tracking process. Vibrations and

movement can temporarily "break away" the diode/corrosion causing this

CPD.

• Voltage surges can also destroy the diode. At least long enough to

warrant a return visit!

• The test point locations will determine the outcome. If CPD is on any of

the downstream output TPs, it may be the output seizure screw or

connector. Otherwise, continue down that leg. Look for housing

terminators.

• If CPD is on the Fwd input TP and not on the output TP, the problem

could be the input seizure screw or connector. It could also be

downstream, though.

• The levels on the reverse input test point may be too low to see, which

might warrant a pre-amp. Otherwise, attach to the reverse output and

terminate reverse input pads one at a time to determine the offending

reverse input leg.

• If you view the reverse spectrum from a bi-directional test point with an

analyzer, you could overdrive the frontend of the analyzer with too much

forward path signal and cause intermodulation within the test equipment.

In order to see the reverse ingress, the instrument is in its most sensitive

mode. Both forward and reverse signals are going directly into the mixer

input. The high level forward channels will cause intermodulation

products in the frontend of the meter. This will happen on any type of

analyzer.

• Use a low pass filter to block all the forward channels. You can use a

diplex filter, but it’s cumbersome. The insertion loss may not be

calibrated, and it may not be DC blocked. This is why Acterna built the

SDA units with a built-in, switchable, low-pass filter to block the forward

channels.

Test Location Considerations

Because the return path signals are low in level, it may be warranted to use

a preamp.

1 2 ... 349 350 351 352 353 354 355 356 357 358 359 ... 409 410

Sin comentarios

Wavetek 147 Especificaciones Pagina 354