My first 50 Ohm RF dummy load when I was a kid was a 100 Ohm, 200 W wire-wound resistor with a slider tap I set at halfway. I think I could have used it with a capacitor to tune AM radio stations. I learned a lot.
When your getting to the higher frequencies then you might want to start thinking about the leads to the components as well. cant beat a good old lump of carbon to form a nice 50 ohm load.
That RF Analyzer is co cool!! The green screen CRT display combined with the floppy drive... Remember when the old word processors had a floppy drive, everything used to have a floppy drive on it and I thought it made things that much better. USB ports are far more useful but they have a cheapness to them 🙂
I use 10, 500 Ohm, 2W carbon resistors, (I have a few thousand of them,) mounted in parallel, (of course,) between 2 pieces of PCB material for my QRP dummy load. With essentially no lead length other than the PCB material, careful placement and connector positioning I've found it useful to well past 70 cm without problem.
I'm glad this is exactly what this video was. I have some basically identical resistors and I used to (a long time ago) work on VRC-524s, and they have an air coil in them (very) approximately the size and shape of the windings of that resistor. We had some very large 1kw RF 50 ohm loads with N type connectors on them. I don't know whats in them other than oil since they make a sloshing sound, but they're rated up to 1GHz. Little jealous of your equipment. Whenever I wanted to do this I had to use a frequency generator and analyzer to get an idea of the actual impedance across a spectrum.
At one time I used to have an old military dummy load which was inductive, and had an attached variable cap to tune out the inductive reactance. I don't remember if I ever knew what equipment it was meant for.
I also seem to remember vaguely, discussion about trying to find matched wirewound resistors, and connecting them in parallel with the windings opposite to minimize inductance. I don't believe it worked
One of the holes in my hobbyist learning curve is how to properly terminate an oscilloscope, to accurately take measurements and to protect the DUT and scope. Please make such a video. I'm getting old, so make it really, really easy to understand and even easier to remember Thanks!
I visited a University research lab that were using a wire wound 50Ohm resistor to impedance match a 50Ohm coax. They were using 100ns pulses on the line. Tells you all you need to know about the education system.
Maybe if you knew what frequency the baby bottle inductive resistor might be used it... could it be shunted with a capacitor so it resonates at 50 ohms....?
"They're garbage, just don't use them". ..... for any RF applications, unless you also want the inductance! For DC and audio they might be just the ticket.
I knew about resistor inductance issues, but thought those are not that important on HF. And then I built a 100w dummy load that behaves exactly as that bad example :( barely usable up to 3Mhz. Now a dumb question: could adding a capacitor in parallel maybe fix it?
so aside from an increase in power rating, is there an advantage to using 1 50ohm resistor compared to using multiple resistors in parallel to arrive at 50 ohms?
The loop formed by the leads and body of the resistors produce an inductance, so minimizing that decreases total inductance of the load. Also, many of those inductors in parallel decrease inductance as parallel inductance are like serial capacitance.
Wonder what the change would be if you slipped a piece of copper pipe over the big resistor ,to make a shorted turn on that inductance, or put a steel screwdriver shaft in, that served as a very lossy core.
0:10 I'm deeply offended (LOL !!!) by the "10Mhz" on the label just visible at the bottom of the video frame. * MHz ;-) !!!!! Hmmm... More seriously, perhaps you could do a video on the precisely-correct formatting of electrical units (e.g. capitalization), as so many seem to be unaware. For example, below I see a few comments with "Ohm" when it should be 'ohm' to distinguish the unit (ohm, Ω) from the famous ex-human (Georg Simon Ohm). There are general rules about using a capital letter for unit symbols that are derived from names, e.g. Hz; but there are some exceptions. Also, mHz is millihertz, MHz is megahertz. Just a suggestion, as there's a need. 🙂
