[Elecraft] Tuning the ATU on the K2

[Don Brown]

Hi

I use a different method that I developed to adjust the SWR meters in =
the tuners (KAT2, KAT1 KAT100 and KX1 tuner). I first adjust the trimmer =
cap to the lowest voltage on the test point but I don't get overly =
critical about because it will be adjusted later for the optimum =
setting. Then I set the forward pot for the correct power out =
indication. This is all done with a 50 ohm load. Then I change to a 100 =
ohm resistor and adjust the reverse pot for approximately  2:1 SWR =
reading. Then connect a 25 ohm load and check to see if the SWR is still =
2:1. If not then very gently adjust the trimmer cap to make the SWR =
reading the same with a 25 ohm and 100 ohm resistor. Go back and forth =
with the 100 and 25 ohm until the reading is the same but not =
necessarily 2:1 . Once the reading is the same then adjust the reverse =
pot to make the SWR read 2:1. Finally reconnect the 50 ohm load and make =
sure the forward power is correct if not touch up the forward power pot. =
The idea is to get everything so the power out is correct at 1:1 with 50 =
ohms and close to 2:1 with the 25 ohm and the 100 ohm load. You may not =
be able to get it exact, you may get 2.1:1 with one resistor and 1.9:1 =
with the other but that is good enough. The trim cap will very touchy so =
make very small adjustments and recheck the SWR with both resistors. The =
reverse pot will end up set somewhat more clockwise than the forward =
pot.

I made the loads by installing two 50 ohm 3 watt MOS resistors in =
parallel for the 25 ohm into a PL-259 connector and two of the same =
resistors in series for the 100 ohm load. For the 50 ohm I installed a =
51 ohm 5 watt MOS resistor (hand selected for as close to 50 ohms as I =
could find) into a PL-259 connector. You could also use the new dummy =
load from Elecraft. It is important that the load connect directly to =
the antenna connector without any coax so get the dual BNC male to male =
connector for the Elecraft load and get some PL-259 to BNC connectors =
for the 100 and 25 ohm loads. I make the adjustments at about 5 to 10 =
watts.

The method seems to work and I have not seen any problems with it. Try =
it and let everyone know how it works for you.

Don Brown
KD5NDB



  ----- Original Message -----=20
  From: Michael D. Heit KD7YLA=20
  To: Elecraft List=20
  Sent: Friday, November 07, 2003 10:25 AM
  Subject: [Elecraft] Tuning the ATU on the K2


  Has anyone ever used an oscilloscope to tune the ATU C55 during =
initial=20
  CALn procedure?  I seem to have a hard time getting the setting to get =

  to 000. I can pass through that setting, but the closest I can get =
under=20
  normal tuning is around 10 or 11 ... at a low power setting of say 0.1 =
V=20
  I can get 000, but at 5 watts that is so fleeting it seems darn near=20
  impossible. Or is 000 just a dream??

  --=20
  73, de Michael Heit KD7YLA K2 #03776
  "Real Hams do it at a high frequency"


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