Lbw upstairs iflo  cable check

plots:
25 Mhz total power during the tests (.ps) (.pdf)

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The setup (top)

lbw receiver components:  (top)

• dewar
• lbw pol box. This optionally converts from native linear to circular polarization.
• lbw filter bank. There are two boxes (connected by short cables) that make up the filter bank.
• iflo Chassis. Standard chassis with equipment shared by all receivers.
• Rf switches to select 1 receiver
• transfer switch to swap polA,polB cables
• rf attenuator
• mixer chassis. There is a 750 Mixer chassis and a 10 Ghz upconverter mixer chassis
• if attenuator
• fiber optic transmitter.

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 The test results  (top)

lbwPolBox to lbw (page 1)

• Top: lbwPolBox to lbwFilterbox1 The cable between the lbwPol Box and the lbwFilter box1 was loosened 1/2 a turn. PolA  power decreased be 6%, polB did not change.
• Bot: clean & reverse lbwPolBox->lbwFilterbox1: The pol A cable that showed the jump in 1  was cleaned. It was then reinstalled with the ends reversed (polBoxSide went to filterBox1 side). The polA cable was loosened on the polBox side (dashed green..it jumped 1%) and then on the fitlerbox1 side (dashed blue, it jumped .4%). Cleaning and retightening seemed to improve things. The poor connection is probably on the cable and not the polbox/filter box since the largest response stayed with the cable end.

• Top 1360 to 1470 filter: Filter 6 was selected.
• filter box 2 output cables loosened 1/2 turn (dash black and red lines). No change in power
• fbox1 to fbox2 cables, fbox1 side. Little or no change (no vertical flags in plot)
• Fbox1 to fbox2 cables, fbox2 side: PolA (dashed green) dropped by 6% when loosened 1/2 turn. PolB (dashed blue) showed little change.
• Center 1100 to 1800 filter: filter 5 selected:
• fbox1 side: PolA (dashed black) dropped < .2%. PolB (dashed red) dropped by 4%.
• fbox2 side: PolA (dashed green) dropped < .5%. PolB (dashed blue) dropped by .5%.
• reverse polB fbox1 to fbox2 cable: The polB cable was removed, cleaned, and then reinserted with the ends switched. PolB fbox1 side and polB fbox2 side dropped by about 2% when the connectors was loosened 1/2 a turn. The poor connection is probably in the polB cable and the connector on the fbox2 side.
• Bottom swapped polB cable filter 3 (1230-1470) and polB filter 5 (1100-1800).
• The polB cable from filter 3 (1230-1470) was moved to polB filter 5 (since filter 5 is used more than filter 3). Loosening the cable on filter 5 polB fbox1 side showed no change. Loosening polB filter 5 on the fbox 2 side (dashed red) dropped the power about 1.5%. This is consistent with the center plot that showed that the poor connection was the cable and the connector on the fbox2 side.

• Tapping on 750 mixer chassis front panel: We could not take data with the 750 mixer chassis open since the cables would not reach. Instead we tapped on the front panel. PolB (dashed green) increased in power by 4% after we started tapping. The chassis was open and we found 3 cables that were loose. Tapping on the front panel must have decreased the attenuation in the loose connector. The cables were tightened and the chassis reinstalled. Tapping the front panel no longer changed the signal level.

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Conclusions:   (top)

• 3 loose cables were found in the 750 Mhz mixer chassis. This could have caused unstable power levels if the observation used this mixer.
• The lbwpolBox to fbox1 polA cable showed a 6% drop in power when loosening 1/2 turn. After cleaning and reversing the cable, the drop was 1%. The cable was probably loose or dirty.
• filter 6 (1360-1470) fbox1 to fbox2 polA dropped by 6% when loosened 1/2 a turn. I'm not sure if we then cleaned or swapped it. Probably need to recheck it.
• filter 5 (1100-1800) fbox1 to fbox2 polB dropped by 4% when loosened 1/2 a turn. Swapped polB cable with filter 3 (1230 -1470). Now only drops 1% when loosened on fbox2 side.
• replace the cable that is in filter 3 polB (1230 to 1470)
• replace connector fbox 2 side polB filter 5.