Brown dust in waveguide

[jp498]

Helping someone with a 1935 setup today,,, They were getting some weak returns, so I checked the software settings and wasn't able to make much improvement with tuning/gain/sea/rain.
I opened the dome and was clean everywhere (no salt) no cracks in the antenna plastic... There was some brown dust in the waveguide interface between the electronics and antenna. I blew it off before I took a photo..
I shut the lid, spun the antenna a few times, opened it back and it remained clean. Turned it back on and got quite a bit better picture.
Any idea where this dust come from?
I'd assume it's something metal if it hurt the signal but it looked like espresso grounds.

 

[Johnny Electron]

It sounds like rust. 1935 is an open array. I'd open it up and take the cover off the motor area and see if you see signs of corrosion. You might take off the array and check the rotary joint for signs of corrosion. Unfortunately, too many folks do a poor or no sealing job on the array. The array should be sealed well to prevent water intrusion, the bolt gets a bit of sealant for the threads to keep it from seizing long term and then the bolt head gets covered to keep water out of the paint scratches that inherently happen with the bolt and washer tightening down into the paint surface. Skip any of these steps a price will be paid at some point. The worst being not fully sealing the array. You should never see the crack where the array meets the rotation joint all 360.