5
Agilent Technologies Noise Sources: 346A, 346B, N4000A, and N4001A
12. For the 346B, if the ENR is not within specification, refer to the supplied 00346-90024 Installation Note for
instructions on how to tune the attenuator to meet the ENR specification at frequencies above 12 GHz. The 346A
should not require polyiron tuning.
13. Retest ENR after tuning the attenuator.
14. If the ENR is still out of specification, substitute another resistor for R7 from Table 2. Decreasing the bias current
by 10% increases the ENR response by 0.5dB at 10MHz.
15. Retest ENR.
A.2 346A/B Replacement Bulkhead Assembly Installation Instructions:
1. Ensure that the bulkhead was shipped with a small envelope containing a resistor.
2. Ensure that the value of the current marked on the bulkhead matches the value on the envelope.
3. Ensure that the value of the current marked on the envelope corresponds to the resistor value and part number
provided (refer to Table 2).
4. Ensure that the resistor value on the envelope matches the resistor supplied.
5. Disassemble the Noise Source by removing the two flat head screws near the output connector and slide the
bulkhead out of the housing.
6. Remove the two flat head screws near the BNC connector and slide out the printed circuit board assembly.
7. Install the replacement bulkhead.
8. Check the resistor installed (if any) in position R7 on the 00346-60001 printed circuit board; refer to Figure 1-
00346-60001. If it matches the resistor supplied, it is not necessary to install it in the printed circuit board.
9. Install the supplied resistor in R7 position (refer to Figure 1- 00346-60001).
10. Reassemble the unit and perform a preliminary ENR measurement.
11. If the ENR is not meeting specification, substitute another resistor for R7 from Table 2.
Decreasing the bias current by 10% increases the ENR response by 0.5dB at 10MHz.
12. Retest ENR.
A.3 346A/B Replacement Printed Circuit Board Assembly Installation Instructions:
1. Disassemble the Noise Source by removing the two flat head screws near the BNC connector, and slide out the
printed circuit board assembly.
2. R7 is not loaded in the replacement printed circuit board assembly. Install the same value of R7 as in the printed
circuit board being replaced.
3. Install the replacement printed circuit board, reassemble the unit and do a preliminary ENR measurement.
4. If the ENR is not meeting specification, substitute another resistor for R7 from Table 2.
Decreasing the bias current by 10% increases the ENR response by 0.5dB at 10MHz.
5. Retest ENR.
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