Help needed to control KPA500

[Barry Simpson]

 I have been using my KPA500 for some years with my TS990. The TS990 USB
port runs my logging program, Turbolog 4, and the TS990 serial port is
connected to the KPA500 serial port for automatic band change. All works
well.

Very recently, I bought an SDRPlay RSP2 so I could have a better bandscope
display than the TS990's. As the SDR needs the USB port to operate, I had
to rejig the logging program arrangements such that I now run the logging
program from the TS990 serial port through an FTDI serial to USB adapter.
That works fine.

I then needed to adapt the arrangements to get the KPA500 working from the
TS990 serial port at the same time. After a few Google searches and
enquiries on the TS990 reflector, I obtained a serial port Y cable which
plugs into the TS990 with one branch of the Y going to the serial/USB
adapter for logging (works fine) and the other branch going to the KPA500
though a two wire circuit comprising pin 3 of the TS990 serial port to pin2
of the KPA500 through a 1N4148 with the cathode end to the KPA500 and pin 2
of the TS990 serial port through a 2.2k resistor to pin 2 of the KPA500
serial port. Pins 1,4 6 and pins 7,8 of the KPA500 serial port are wired
together.

I tried to post the circuit embedded in this email but the reflector owner
bounced it as being outside the guidelines. That is why my explanation is
so convoluted.

All appropriate baud rates and other KPA500 settings are correct but the
KPA500 simply does not do any band changes except if, for example, the
logging program drops out (which it does very occasionally) and I click the
mouse to reset it. Then the KPA500 jumps to the correct band. Presumably
the resetting of the logging program produces a pulse and that activates
the KPA500.

Obviously what I am doing is not the right way to go about the problem and
it would be appreciated if someone could put me on the right lines.

Many thanks

Barry Simpson  VK2BJ
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[Jim Brown-10]

On 8/18/2017 6:38 PM, Barry Simpson wrote:
> I then needed to adapt the arrangements to get the KPA500 working from the
> TS990 serial port at the same time.

Hi Barry,

You might want to re-think WHAT control of the KPA500 you need. The
KPA500 is quite good at VERY quickly sensing the frequency of the RF
driving it, and changing bands as required.

The ONLY control I have been between my rig (a K3) and the power amp is
the AMP KEY signal to put the KPA500 in TX mode. All that takes is an
RCA cable between the rig and amp (as long as there's an RCA on the rig
for AMP KEY), and if the rig's AMP KEY is on a different connector, a
suitable adapter or cable with that connector one end and an RCA on the
other.

When I want to change bands, I simply give the amp a dit on CW or tap
the mic on SSB, and the KPA500 is on the right band.

I hope you know that ALC should NEVER be used as the primary control for
output power, because that is a recipe for nasty distortion -- splatter
on SSB, clicks on CW. Rather, we should ALWAYS set power by varying the
output of the rig so that we get the desired power from the amp. My KPA
will get to full power with 25-30W drive, depending on the band.

73, Jim K9YC

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