[Elecraft] Re Remote KAT500

[Paul Wilton]

On military equipment which has to be sealed from the elements there are two main approaches:

1) use a very well sealed metal box with o-rings etc. This will drag in some moisture owing to hearing/cooling cycles. You mitigate this by putting a bag of desiccant inside. Seal manufactures will give you the amount of moisture a seal material will leak over time. Multiply it up by the number of cycles then work out how much moisture the desiccant needs to absorb. 
2) for those enclosures which cannot be sealed for operational reasons (such as a rugged outdoor microphone), use a GoreTex type breather as discussed for pressure equalisation but back it up with a bag of desiccant in the box. 

If you do the maths, you will find that a bag of desiccant can last a very long time even with the GoreTex type breather. On one project, even under worse case circumstances (which included unpressurised flight to 30,000feet), the small bag of desiccant would last 15 years. 

The good news is that a large bag of silica gell is not that expensive. Just don't split the bag and then get it wet........


Paul Wilton
M1CNK