InsertionVSWR of Chinese 1-9 balun module – that load resistor

InsertionVSWR of Chinese 1-9 balun module showed a 450Ω load attached to the DUT, and I have been asked to explain further.

Above is the load resistor just visible to the left of the spring terminals on the module. The idea is that the leads need to be very short to avoid unintended / undesired impedance transformation.

Above is a close up picture of the load. It comprises two 1% 1210 SMD resistors, 1000Ω and 820Ω soldered back to back, and 0.5mm copper pigtails for connection. The parallel connection calculates to 450.5Ω.

It is the 1000Ω resistor that is visible in the pic, 1001 is the code for a 1% resistor of value 100 x 10^1.

I have found the easy way to make these is to line up the two resistors in a pair of tweezers and generously solder both ends quickly, there will be an excess of flux, leave it there.

Now form a single piece of 0.5mm bare wire (stripped from LAN cable) into a U shape just a little narrower than the resistors. Push it down over the resistors and hold it all in place with a toothpick, and offer a clean hot iron quickly to one side and let the solder melt, then quickly the other side and let it cool.

Trim the U end off, and trim the other ends to a convenient length.

The resistors can be bought on Aliexpress for a couple of dollars per hundred.

Too easy?

The 1210 resistors are relatively large SMD parts and easier for beginners to solder. I also use 0806 resistors as they solder across 0.1″ (2.54mm) machine pin strips which makes convenient means of connecting and changing calibration parts on some fixtures.