Re: SSPA cooling at mast-head

Bob Lockley VK6KW

Yes David,

You will only get condensation on any cool surfaces within the box if warm moist air is drawn in to it.

In your case the temp inside during operation is likely to be higher than ambient so condensation is unlikely unless on the inside wall of the outer shell. Drawing fresh air through a ball of stainless steel wool will reduce the intake humidity as well as other undesirables, installing an internal ‘chimney’ so that exhaust air is drawn from nearest the top of the cabinet will ensure the removal of the warmest (most humid) air and further reduce the problem.




From: ukmicrowaves@... [mailto:ukmicrowaves@...]
Sent: Sunday, June 19, 2016 11:06 PM
To: ukmicrowaves@...
Subject: Re: [ukmicrowaves] SSPA coooling at mast-head



Hi David

Yes, the method proposed should work. Keep the hot and cold air as far apart as possible at the entry and exit points to avoid too much recirculation. I have two small axial fans outside the box on my 10GHz system, they worked fine for several years but you will need to clean the spiders out from time to time. They are well protected from rain with a plastic hood covering them. If the heatsink is outside the box and the PA inside you need to consider how the interface between them will be waterproofed. My 10GHz system has been at masthead for 16 years now without any failures so I wouldn't get too hung up about potential moisture issues, so long as you make sure condensate can't build up inside a sealed box.

I'm looking forward to hearing a big signal from IO81 soon!


John G3XDY


On 19/06/2016 14:10, g4asr@... [ukmicrowaves] wrote:

Hello,  I am building up a 23cm masthead mounted system.


The 200W sspa has two blowers associated with heatsink and I am mounting this inside the masthead box.


What is the preferred method of dealing with the air flow?


Do I have two holes underneath, one for air entry and one for expelled air, suitably engineered of course.


I dont like the idea of dragging cold air into a warm box. Wouldnt this cause moisture issues?


I need to keep the sspa cooled without having a box full of water!


I can mount the heatsink externally on the box and have the blowers in the open air.  Reliability?


Any suggestions how others have done this will be gratefully received.

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73 David G4ASR 







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