IN3LBQ on the Hühnerspiel (Amthorspitze) - photo by IN3OTD

Motorola 58D09575U dummy load measurements

A while ago I was looking for a dummy load to test a power amplifier for the 23 cm band (1296 MHz). And, of course, eBay is one of the first places to check to see what's available and at which prices.

Amongst all the dummy loads listed there, the choice fell on a cheap item described as "Dummy Load DC 4 GHz 200W" and whose description added also "Motorola PN 58D09575U"; below is a picture of the dummy load, as it arrived.

Motorola 58D09575U dummy load

Indeed, there is a sticker on it saying "58D09575U", but no reference to being a Motorola part. Anyway, what's important is the dummy load actual performances; for what concerns the power rating, at the moment I cannot test is at a high power (the above mentioned power amplifier is still only on paper) but I had the opportunity to have the dummy load characterized with a vector network analyzer up to 6 GHz.

The graph below shows the measured return loss and the corresponding SWR; note that the load has a nice "dip" just around the 23 cm band, but after that its impedance starts to deviate significantly from 50 Ω and at the specified 4 GHz it sorta works but not very well.

58D09575U dummy load S11 and SWR

Bottom line: this dummy load is good up to about 1300 MHz, beyond that its performances deteriorate rapidly. All in all, not too bad for its price anyway.