[Elecraft] KPA-500 Question

[Don Wilhelm]

  Fred and all,

As Dick's post stated, the K3 band data outputs can be paralleled with 
the KPA500 lines.
The KPA500 has internal protection diodes to isolate it from external 
band decoders that might damage the KPA500 band data input circuits.

The only "catch" is that currently the K3 has internal pullup resistors 
to 5 volts on the band data outputs.  If the band decoder devices have 
their own pullup resistors (especially those who pullup to +12 volts), 
the K3 and/or the band decoder may have problems because of differences 
in the supply voltage to the pullups, and the cure is to add series 
diodes (with the cathode end toward the K3) to the inputs of the band 
data decoder.  The diodes prevent current from the external decoder's 
pullup resistors from flowing into the K3.

The KRC2 used with the K3 avoids this situation since it uses the AUXBUS 
signal to determine which band the K3 is on.

73,
Don W3FPR

On 7/10/2011 2:25 PM, Fred Maas wrote:
> Thanks for reply.  That is what I thought.
>
> I am not familiar with the various outboard devices to which you refer (as
> have never needed them).  I am not suggesting that the KPA500 needs
> additional antenna outputs though that is one way to do it.  That would
> constritute an internal antenna switch.  The KPA500 represents many upgrades
> from my 1980's amplifier so I am surprised that my 80's amp has a capability
> that the KPA500 doesn't.
>
> The band data information from the K3 goes to the KPA500 to tell it what
> band it is to be on.  Are you saying this can be paralleled safely and also
> instruct another device?  I would think such might not be compatible and a
> risky thing to do.
>
> In my set up (with an old Yaesu FL-7000) the band data information from the
> K3 goes to the FL7000 to tell it which band to be on.   The FL7000 then
> associates one of four antenna positions with a band, this is changeable at
> any time and then remembered, and outputs relay control to a remote antenna
> switch.  If the remote switch is not in use, the "antenna" which is
> associated by band is irrelevant.  I am surprised that the KPA500 does not
> have this capability standard and built in with the outboard remote antenna
> relay being an option.  Without this, band changing is not, in fact,
> automatic.
>
> 73,  Fred
>