[Elecraft] Cal AT100 SWR bridge

[Don Brown]

Hi

I have developed a different technique for adjusting the SWR bridge in the KPA100, KAT100 or KAT2. First I adjust the null as in the manual instructions. I have made up some calibration resistors of 25, 100 and 50 ohms. These are 3 watt MOS resistors mounted into a PL259 connector. The PL259 plug is screwed directly onto the KPA/KAT100 SO239. When doing a KAT2 I use a BNC to PL259 adaptor. Use the 50 ohm first to set the null. Then connect a accurate watt meter or scope to set the forward power out correctly. Disconnect the watt meter and connect the 25 ohm resistor adjust the reflected pot for a 2.0 to 1 SWR reading. Then connect the 100 ohm resistor. If the SWR is not 2.0:1 then very slightly adjust the null cap so the reading is the same with the 25 and 100 ohm resistors. When you get the reading the same then readjust the reverse pot to bring the reading to 2.0:1. Connect the 50 ohm resistor and make sure the SWR is 1:1. All of the measurements are done at about 2-5 watts. The resistors will take up to 10 watts for a few seconds. This is usually long enough to make the settings. If you fill the PL259 void around the resistor with silicone rubber the connector will act as a heat sink and the assembly will take more power. Maybe up to 25 watts for a few seconds. Use GE Silicone II for the fill. It is alcohol based and does not corrode electrical connections like silicone with the vinegar smelling ascetic acid based silicone. You should find GE Silicone II at most hardware stores.

Don Brown

  
  ----- Original Message ----- 
  From: Rich McCabe<mailto:r.mccabe at 1967z28.com> 
  To: Elecraft Reflector<mailto:elecraft at mailman.qth.net> 
  Sent: Thursday, September 23, 2004 10:31 PM
  Subject: [Elecraft] Cal AT100 SWR bridge


  Is there any tricks (or improved techniques) on adjusting the SWR bridge in 
  the tuner? I just finished a tuner and everything checked out and calibrated 
  very easy. But I may have a SWR that agrees on my Daiwa in the line 16" away 
  or it may be as high as 4:1 on some bands even when the tuner says it is 
  flat or near flat.

  I have adjusted C31 for minimum reading (.01 volts) and the null is small so 
  I really cant center it in the null easily.

  I also had a problem with oscillations on 40 meters and I think I read 
  somewhere it could be a grounding issue. So I am going to go back and do 
  some more sanding.

  Any tips or comments.

  Thanks,

  Rich 


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