Hi, trying to clean and replace o rings and seals to Ras, can't for the life of me remember how to remove front block (white coloured base) from Ring clamp (main body of Ras) after removing piston,guide pin etc. any idea's ?

For calibration and measure noise figure of our receiver unit we
used two points method, which require two noise sources with d i f f e r e n t R F b r i g h t n e s s temperature. For example ambient temperature (“hot” load) and liquid
nitrogen temperature (“cold” load).

unscrew the knurled ring from the RAS Head. Sometimes using a Phillips screwdriver as a turning handle thru the guide screw hole. After ring is removed the base is usually stuck on the body. I used to use a chisel tip fiberstick to get into the seam and twist to spread it apart, you can use a flat head screwdriver (with extreme care). then all of your o rings and seals are accessible for cleaning. We used to use Acetone. Almost forgot, on the bottom of the unit that faces glass there are 3 flat head screws. The big one in the middle has a spring behind it with a tiny o ring to be replaced, push down on screw twist 90 degrees for removal then reinstall in reverse order. DO NOT mess with other screws other than flushing them with cleaner.