RF,IF attenuators description & switching times


Normal operation of rf,if attenuators
Attenuator failures
Measuring the switching times
The IfAttn 2nd 4db attenuator problem.
Turning off switch verify caused adjustment problems.


    The upstairs if/lo has two sets of attenuators:  rf attens (before the mixer) and if1 attens (after the mixer). These attenuators go 0 to 11 db in 1 db steps.  Internally the attenuators consist of:
This combination can generate value of 0 thru 11 db. they are accessed via a 4bit word.

Normal operation of the attenuators

    In normal operation the adjpwrif1() procedure is used to adjust the upstairs power levels. The sequence is:

    These attenuators are attached to the gpib bus via the 87130 switch controller. To set an attenuation value the program will:

Attenuator failures

06mar17:Measuring the time for 1db steps

    On 06mar17 the proc/test/attntm.proc routine was run to measure how long it took for the attenuators to make 1db steps. The procedure was:

The plots show the time for the 1db steps

06mar17: 1 db steps with RF attenuator. switch verify off (.ps) (.pdf)

06mar17: 1 db steps with IF attenuator, switch verify off (.ps)  (.pdf)

08mar17: 1 db steps with RF attenuator, switch verify on (.ps) (.pdf)

The problem with the 2nd 4db attn of ifattenPolB

    On 09mar17 felix inspected the polB IF attenuator in the dome. He found that the cable that plugged into the atten card had  the pin for the 2nd 4db attenuator bent. This was causing the atten switch to not close. He fixed the pin and it now works correctly.

Turning off verify caused power adj problems

    When the adjpwrif1() routine was written, i timed how long it took for the attenuators to switch. At the time  I saw that they were always switched by the end of the command to set the attenuator (This was with switch verify on). So the adjpwrif1 sequence was:

When the switch verify was turned off, adjpwrif1() was not changed. The caused the following:

On 09mar17 i put a 1 second delay in the adjpwrif1() routine after the  set attenuator values, and before the next power meter reading.. this fixed the problem.
    Note that the downstairs if2 attenuators are not driven by and 87130.. so they do not have a verify option. The adjpwrif2() routine always had a 1 second delay between the setting of the attenuator and the reading of the power meter.


processing : x101/170306/attntm.pro

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