[Elecraft] KPA100 Power Surge Advice

[Geert Jan de Groot]

Hi,

In addition to Mike's response (always happy to read his comments!), I 
think it is useful to give some additional hints as you may need a 
better understanding of the configuration you have.

The Elecraft K2 is a 15W QRP transceiver, with the optional QRP 
antennatuner and the battary option in the top lid.

When Elecraft introduced the 100W KPA option, the basic idea was that 
the top lid could be replaced with the KPA100 to get 100W output. When 
the KAT100 antenna tuner was introduced, it would add another (lower) 
box that was supposed to sit under the K2/100 radio. Switching between 
QRP portable mode (with battary) and 100W version meant switching the 
top lid.

The KPA100 doesn't have any indicators. The KAT100 tuner does: ANT1/ANT2 
selection, LOW/HIGH power (enabling or disabling the KPA100 amplifier, 
which could be switched to be bypassed for QRP power levels) and a LED 
bar to indicate SWR.

I think it was Lyle KK6P (of KDSP2 fame) who conceived a different 
approach: the frontpanel of the KAT100 tuner was available in two 
versions, one for the low KAT100 box, but also a bigger frontpanel that 
would be the same size as a K2 radio. You would buy a "K2 empty box" and 
in this second box, one would install the KAT100 tuner (bottom) and the 
KPA100 amplifier (top).
The QRP antenna tuner / battary would be in the original top, that stays 
on the K2. Connecting the boxes together would give a 100W radio with 
PA, 100W antenna tuner; disconnecting the two would give a the K2 
portable radio with builtin battary. I built this configuration.

Since you mention "separate enclosure" I suspect this is the config you 
built too.

It seems that information about this configuration has gotten a bit lost 
over the years. The KAT100 module design was made to allow for this; for 
instance, it had a BNC connector so that the input of the KPA100 
amplifier could be connected to the K2 this way. Power to the twin boxes 
would be via the 20A powerpole connector on the KPA100 module; the 
KPA100 module has a low-power power connector that would normally supply 
the K2, but in this configuration would power the KAT100 module. The 
KAT100 module, as well as the K2 radio itself, has a 2.1mm barrel jack 
that if you would use interconnect powercables, would power the K2 (from 
the KPA100 and the KAT100 module). And the AUX connector (DE9) on K2 and 
KPA100 on the twin box would be connected via a short jumper cable. 
There are a number of options here, depending on how this was built 
(hence 'information a bit lost').

I need *three* cables between the two twin boxes: a coax jumpercable to 
interconnect the BNC antenna ports, a powercable to power the K2 from 
the twin box, and a DE9 jumpercable to bring AUXbus, 12VCNTL, ALC, 8R 
and ground between the two boxes. Please verify you connected al three 
cables; I have my suspicions about the DE9 cable.

Now,to your question. First, the KPA100 module (again / still) does not 
have a power indicator. The KAT100 module *does* have indicators. And 
they only light if the KAT100 module senses power from the K2 radio 
(that is now it "switches off" if the K2 is switched off).

So, the first question is whether the K2 and the twin box is connected 
correctly. The twin box has 2 AUX DE9 connectors (one on the KPA100, one 
on the KAT100); please verify it is connected to the right one.
(In my case, I did not place the KAT100 DE9 connector because it didn't 
serve a purpose in my my radio config, the twinbox is made to use the 
DE9 of the KPA100 module!).

Another question is whether the KIO2 module, that provides the DE9 
connector on the K2 radio, actually still supplies +12V on pin 8 of the 
DE9 connector. The voltage is only used as "sense voltage" on the 
KAT100, not to power the tuner.

The K2 senses if it has the twin box connected during powerup. You can 
do a few checks: pressing the ANT1/2 button will flip the relays in the 
KAT100 if it was found during powerup, but will flip the relays in the 
KAT2 QRP antenna tuner if not (the relays in the KAT100 are LOUD!). The 
POWER knob will go to 110 if the KPA100 is found, bit only to 15 (or 10) 
if the KPA100 is not found.
If the K2 radio has the builtin battery, then you should be able to see 
the power supply voltage if you select it using the DISPLAY knob and 
then switch the power supply on and off (the K2 doesn't handle this very 
gracefully, kindly powercycle the K2 after this test).

In short, the problem description is a bit terse but I hope this message 
gives some more background about a config that is partially forgotten in 
past years and not very well documented.

And whatever you do, NEVER CONNECT A NORMAL RS232 SERIAL CABLE IN THE 
DE9 of a K2 OR KPA100 MODULE. A "serial device" only connects pin 2, 3 
and 5, NOTHING ELSE.

73, Geert Jan PE1HZG