[Elecraft] KPA-500 from Orlando

[Jack Brindle]

Another way is to add series diodes between the driver and the  
amplifier. You will want to have pullups on the amplifier side.

Accidental powering is a major, but for the most part unrecognized,  
problem with low-power equipment when one is not powered. We have to  
provide isolation circuits to keep power from one system from  
accidentally activating another. In your case it is the XCVR power  
powering the amp's MCU. Microprocessors require amazingly small  
amounts of power these days, and will quite readily power themselves  
through their I/O pins, although it actually may end up destroying the  
processor.

In your case, since the band data is one-way, adding the isolation  
diodes on the amplifier side actually provides a good solution. Use a  
schottky diode,like a 1N5711 for good results. And don't forget the  
pullups on the amplifier side of the diodes.

Jack Brindle, W6FB


On Feb 15, 2011, at 4:47 PM, Phil & Debbie Salas wrote:

> "Wayne,  I have my THP HL-2.5kfx, is there a way to control both via  
> the K3?
> I would
> like to select the device to use based on conditions without going  
> through a
> lot of switching.  Bill K9YEQ"
>
> Unless the design has been changed recently, either the HL1.5 or the  
> HL2.5
> (or maybe both - I can't remember) load down the band data lines  
> when the
> amp is turned off.  If you have a stiff enough band data source  
> (like a TTL
> driver), you can actually partially power-up the processor in the  
> THP amp
> via the band data inputs when the amp is off.  So you may have to  
> switch the
> band data lines between the KPA500 and the THP amp.  Or use band  
> data for
> the THP amp, and the KPA500 RF sense for KPA500 band changing (the  
> KPA500 RF
> sense works VERY well).
>
> Phil - AD5X
>
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