[Elecraft] Builder Alert #17: More accurate current metering

[Wayne Burdick]

APPLICABILITY

K2 serial numbers 0001-2855

BACKGROUND

The K2's current readings (in V/I DISPLAY mode) can be made both more
stable and more accurate by the addition of a single capacitor. The
capacitor goes from the "ISENSE" line to ground (Control board). This
was brought to our attention by Larry, W1HUE/7, who discovered that RF
was getting into the ISENSE line, especially on 160 meters. By adding a
cap on ISENSE, he dropped his 160-meter transmit-mode current reading by
over 20% and reduced the "bouncing" from one value to another. 

We have since confirmed this on several other K2s. It may eliminate
false "HI CUR" indications on the lowest bands that were due to the
artificially high readings caused by RF on the line.

MAKING THE MODIFICATION

You'll need a capacitor of anywhere from .01 to 0.1 uF (10 to 100 nF),
ceramic or monolithic. Solder the capacitor across R7 on the Control
board, keeping leads short. Make sure the capacitor doesn't contact any
adjacent pads or component leads.

In addition to this capacitor, we recommend increasing the size of C42
on the Control board from .01 to 0.1 uF (or larger; ceramic or
monolithic, not electrolytic). If you have installed a KPA100 option in
your K2, you have probably already done this, since an 0.1-uF cap is
supplied with the KPA100 kit for use at C42.

If you don't have any suitable capacitors in your junk box, send a
request to parts@elecraft.com and we'll send you two 0.1-uF caps at no charge.

NOTE: Two capacitors will be supplied for this mod in all K2 kits with
s/n 2856 and higher, and their installation will be covered in
the manual errata sheet.

73,
Wayne,
N6KR