Re: [K2] Remote KPA100 Bias Current Adjustment

Posted by Don Wilhelm-4 on May 12, 2011; 4:37am
URL: http://elecraft.85.s1.nabble.com/K2-Remote-KPA100-Bias-Current-Adjustment-tp6350558p6354485.html

  Brian,

Don't worry about the fan - so set it to "nor".  Observe the current
into the KPA100 and add 400 ma. That is your target for the initial
collector current.  Take the KAT100 out of the picture for this
adjustment - unplug the AUX DC cable from the KAT100.  When you go to CW
TEST mode and TUNE (with power set to greater than 11 watts), the
current rise should be set as close to 400 ma as possible - if the
receive current is  230 ma, you would adjust the bias so that the
initial TX current is 630 ma.  The current will increase rapidly during
the TUNE interval, so watch you DMM initially - the first displayed
reading may be invalid due to timing, but the second is the reading you
want.  Exit and re-enter TUNE as many times as required to get it right.

73,
Don W3FPR

On 5/11/2011 11:35 PM, Brian - N5BCN wrote:

> Hi Don,
>
> Perhaps against my better judgement, I adjusted the bias current of the
> KPA100 in the KAT100-2 remoted from the K2.  Now I'm thoroughly confused!
> :-(
>
> The current measurements of the KPA100 in the K2 make sense to me:
> Power<  11 W, Current ~ 380 mA
> Power>  11 W, Current ~ 520 mA
> Power>  11 + Fan on Lo, Current ~ 565 mA
> Add 400 mA for the bias current, and you get a target of ~965 mA.
>
>
> The current measurements of the KPA100 in the KAT100-2 remoted from the K2:
> Power<  11 W, Current ~ 88 mA
> Power>  11 W, Current ~ 229 mA
>
> This makes sense to me because the KPA100 is providing power to the KAT100-2
> now, which apparently draws a lot less current than the K2 plus options.
>
> Here's what doesn't make sense to me:
> Turning on the fan now that it's in the KAT100-2 does not increase the
> KPA100's current draw at all, but it makes the current draw of the K2 go up!
>
> The only connection between the K2 and the KPA100/KAT100 is the data cable
> connecting the RS-232 ports.  Is this data cable providing current to power
> the fan?!  If so, how do I factor all this into figuring out a target for
> the bias current adjustment?  Do I add 400 mA to the 229 mA value and be
> done with it?
>
> Thanks for straightening me out!!
>
> 73
>
> N5BCN - Brian
>
>
>
> -----
> K2 #6800 KPA100/KAT100-2, KSB2, KAT2, KIO2, K160RX, KNB2, KAF2, LP-PAN/K2 w/ Pre-amp, SignaLink USB
> --
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