Hello guys, Thank you all for the replies. I've been doing some research, & I've found that a Carbon Resistor when heated will exhibit reduced resistance as I'm witnessing with this Dummy Load - so it seems that what I'm seeing is probably normal behaviour although not good. After looking closely at the Resistor in this, I see it's a "ER50SP" Siliconised Carbon Resistor rated at 50W continuous use. I know Zetagi are renowned for exaggerating claims, but claiming this Resistor is capable of handling 1KW is nothing short of ridiculous. Here is the specification of the " TKK ER50SP" Resistor that's inside the Dummy Load: http://www.sanwatsusho-global.com/product/15/15_01_02.html I've checked this dummy load upto 145 Mhz on a friends rig, and at that frequency I'm seeing a SWR of ~1.2:1, so although not great, it's perfectly fine for HF use.