Attenuators, Sampler levels, GTP

Benign causes:

• if attenuators are not changing, when you expect that they should, check that automatic setting for attenuators is enabled (CAOBS$>$enable auto),
• when moving to a new part of the sky or a new frequency (e.g. at the start of your observation) it can take several minutes until the correct levels are reached. If the attenuators are changing, be patient while the correct levels are found.
• you sometimes will get an assistance warning during normal observations when power levels are close to the level where the attenuators will be automatically changed. If the sampler statistics are still 17.3%, and gated total power (GTP) between 1 and 4.5V you can usually be patient and wait for the automatic attenuator setting mechanism to sort this out.
• with higher frequency observations (above 8GHz) rain can cause significant increases in the system temperature, which can result in the need for rapid attenuator changes. Again, the best response is often to wait for the automatic system to find new levels. (Note: the inverse problem will happen again when the rain passes on.)
• interference has affected your gains - as with the rain, it is probably best to leave this to the automatic attenuator setting mechanism. At present, there is little we can do about interference - aside from cursing. A list of handy swear words is available on request.

Less benign causes:

• the gated total power readings can saturate, and give low readings (instead of high ones). The attenuator setting algorithm is then getting conflicting input, and often will not reset attenuators. If the Sampler NEG is 255 (as viewed in the CAMON samp page) increase the attenuator level even if the power level is low or even zero.

For more information about setting attenuators see section 5.2.5 on page .

Be careful about resetting course and mm attenuators while observing as this will cause a step in phase!