tag:blogger.com,1999:blog-973137714505742515.post4558221905451405671..comments2023-10-20T18:19:45.835+02:00Comments on DIYcrap: Homebrew dummy loadflathagenhttp://www.blogger.com/profile/11155798668216436343noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-973137714505742515.post-43512037157025459822016-09-06T23:01:42.762+02:002016-09-06T23:01:42.762+02:00I was too fast in saying that because the series s...I was too fast in saying that because the series sections truly lower the voltage applied to the resistors and thus the applied power. I was thinking in terms of current only. Sorry about that. The rest still applies though, check for parasitics.MarSikhttps://www.blogger.com/profile/04703143981787504455noreply@blogger.comtag:blogger.com,1999:blog-973137714505742515.post-16658208759995630682016-09-03T21:34:41.992+02:002016-09-03T21:34:41.992+02:00Hi. I beg to disagree with your statement about se...Hi. I beg to disagree with your statement about series vs parallel resistors and so would ohms law. Putting 50 1 Watt 1 ohm resistors in series would give a 50 watt dummy load. So would 50 2k5 resistors in parallel.flathagenhttps://www.blogger.com/profile/11155798668216436343noreply@blogger.comtag:blogger.com,1999:blog-973137714505742515.post-39810927424927199972016-08-29T17:13:48.040+02:002016-08-29T17:13:48.040+02:00Those resistors and their declared wattage look li...Those resistors and their declared wattage look like what I used once and there was a lot of parasitic inductance.<br /><br />Also the big plates of copper sum up to some substantial capacitances. Make sure you expect some parasitics as this won't be a clean 50Ω load to much more than couple of MHz. I have something similar (20x 1kΩ blue metal film resistor 0.5W each) and it is good up to 30 Mhz but not more.<br /><br />I used two plates with holes arranged to a circular form and the resistors are soldered between the two plates (resistor sandwich :). The center then has a thick wire connecting the connector's center conductor to the back plate. The front plate is connected to connector ground. The plate distance is much higher (and capacitance drops with the power of distance), but it is still not good enough even for VHF.<br /><br />Btw your setup will only handle 8W (4x 2W)! The series resistors do not count.. only those in parallel.MarSikhttps://www.blogger.com/profile/04703143981787504455noreply@blogger.comtag:blogger.com,1999:blog-973137714505742515.post-3543550023358738922016-08-27T22:08:58.584+02:002016-08-27T22:08:58.584+02:00Be sure to use non-inductive resistors like carbon...Be sure to use non-inductive resistors like carbon composite. Often, the 1 & 2 watt resistors are wire-wound.Chris Crosswhitehttps://www.blogger.com/profile/02999258628596054112noreply@blogger.com