[Elecraft] KPA1500 PIN diode T/R, fans

[Wayne Burdick]

Hi Paul,

To protect the amp and T/R switch, we’re using heavy-duty PIN diodes, very high reverse voltage, and virtually instantaneous detection of high SWR. All possible catastrophic load scenarios have been extensively tested.

On fans:

We started with a humongous custom heat sink extrusion and thick copper spreader, optimized for our packaging. We also use two LDMOS devices rather than one, allowing heat to be distributed across all that heavy metal much more effectively. This slows fan onset time. (Some competing compact amps use inadequate heat sinking, with predictable results.)

Next, we added three large, deep fans. The center fan is controlled independently so it can turn on first, at low speed. In many cases that's all you'll ever hear. Only during high duty-cycle operation are the other two fans turned on. We then carefully manage the speed of all three. 

Ultimately, you have to get rid of the heat. But our goal is always to minimize noise. 

73,
Wayne
N6KR


> 
> *From: *"Paul Christensen" 
> 
> Wayne,
> 
> Congrats on what looks like a very well-designed amp.  I've been
> waiting on
> an amp with these features for a very long time.  Of particular
> interest to
> me is your continued use of PIN diode T/R switching.  Can you describe SWR
> protection to the Rx PIN diodes at the 1.5KW level?  I suspect that a
> fast-detecting SWR switch will be the main focus of protection, as well as
> HV back-biasing of the Rx diodes.  An open or short RF termination
> requires
> over 900V DC to keep Rx PIN diodes from going into conduction.  Can you
> describe this area of circuit protection just a bit?
> 
> Secondly, I know that fan noise is difficult to quantify in words.
> Anything
> particularly innovative you're going to minimize cooling noise?  Thanks!
> 
> Paul, W9AC
> 
> 
> 
> 
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