[Elecraft] Mod to OHR 100W Load

[Mike Harris]

Hi,

A few have asked so here it is.

I wound ten turns of some spare K2 enamelled wire onto an FT57-43 core.  The
wire between the centre pin of the input SO239 and the load resistors was
passed through the core making a 1:10 ratio transformer.  One end of the ten
turn winding goes to the SO239 ground lug, the other goes to whatever socket
you use for the tap.  I fitted a BNC.  End of story, a simple -20dB coupler.

To use it connect the K2 to the load as normal.  Connect the input of the
wattmeter to the tap and terminate the load side of the wattmeter with a 50
ohm load capable of handling 1W or more.  With the WM-2 set to 1W range,
full  scale (1W) = 100W into the load.  Actually just read the mW scale as
watts.

Naturally this works with any QRP wattmeter not just the WM-2.

It is best to terminate the tap with 50 ohms when using it without the
wattmeter.  A 50 resistor soldered into a BNC plug works fine.

For what it's worth.

Regards,

Mike VP8NO (IOTA SA-002)
GQRP 10148
K2 #1400 + KPA100