[Elecraft] K2's ATU "vagaries"

[James Rodenkirch]

While altering my existing antenna system which includes an LDG Z11ProII auto-tuner at the base, I had to do quite a bit of "testing" from the shack; e.g., add a un-un, go to shack, hit the tune switch, watch power out and SWR.....switch to another un-un with a different ratio, follow same procedure. All of this with the K2' internal auto-tuner turned of.
 
The antenna "alteration" I was trying wasn't providing the LDG auto-tuner with Zo values it liked so I was switching the K2's auto-tuner in and trying it across the various bands to see how it "played" with the altered antenna. After an afternoon of this I surrendered and restored the antenna to its original configuration, one the LDG auto-tuner tuned effortlessly.
 
Note: the original system is a 36' vertical with 12 elevated radials an the auto-tuner at the base of the vertical. The LDG has always tuned that configuration effortlessly on 40 through 12.
 
After restoring it back to its original configuration I went through the tuning cycle - K2's ATU off, hit the tune switch....yadda, yadda; that's the configuration I use - ATU off, K2 set to watch pwr out and reflected- the POUT mode. What I found was: the LDG tuned 40 through 12 effortlessly BUT, on 40 meters I observed 5 watts out and 2 watts reflected (prior to all of this, it was zero watts reflected). Given the vertical is back to its 36' configuration one would expect zero watts......so, I retuned several times but, same result. I could tell the LDG was tuning correctly and with 30 through 12 showing no reflected power I kept wondering of the K2 was "acting up."
 
I found the internal ATU manual and start reading up on the "Using the ATU." I found this: 
 
   As an alternative to CALS or CALP, you can tune up the ATU into a 50 ohm dummy load on each band using AUTO mode. This will 
   cancel out most or all of the stray inductance and capacitance so that you can connect your external tuner or resonant antenna.
   After tuning up on all bands, put the ATU in to POUT or SWR mode> The matching network settings will not change.
 
I ran through that sequence and...poof....no reflected power on 40 meters! 
 
Soooooooooo.....has anyone else experienced this "phantom," residual L/C? How does the internal ATU provide/introduce stray L or C while in the off position?
 
I'm not complaining - the "fix" was easy....I'm just curious.....72 de Jim Rodenkirch K9JWV