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'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.
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.
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?
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.
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....?
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.
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. 🙂
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
"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.
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.
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.
Oh yeah, it's nice to actually see why you never use a wire wound for a RF dummy load. 👍
Нет! При применении многих резисторов, появиться паразитная ёмкость. Которая еще сузит, диапазон работы нагрузки.
@@Иван-у7т7п Could you russians pleas stop commenting in your shit*y language?
@@filipamator You should read the translation.
It is probably ok for e.g. VLF submarine communication. RF starts at 3 kHz.
Yep, I've seen special counter wound ones that were good trough a fair part of the HF spectrum.👍
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.
my biggest dummy load is the antenna 🙂
otherwise i just use the 150W carbon resistor load. @@retiredbore378
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'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.
30nH is the inductance of an inch or two of wire.
I wonder what a metallized film resistor would sweep like-I wonder because of the metal it would suffer from skin effect
Would be very Interesting if you could show us what an RF rated 50 ohm "Non-Inductive" Wire wound power Resistor looks like on the Vna.....
I have had bad luck trying to use wire wound resistors for dummy
That's a nice piece of equipment. I could have used one of those years ago. Thanks..
Love that equipment. 😊
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.
100 ohm is in the E12 series 50 ohm is not.
Testet with 300kHz only 🤣
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?
I think that a capacitor in series can "fix it" for one frequency but normally you want board band dummy loads.
Nice!
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.
Interesting. I'll have to experiment with that just for fun.
Inductive Reactance here I come!
That's why professional 50 Ω loads use a block of carbon ! .... QED ........ DAVE™🛑
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....?
Interesting dummy load 😂😂😊😊
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.
Good resistor for a low-pass filter, no?
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. 🙂
Sorry and apologies to Mr. Hertz that is my rubidium
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
Never heard the term "Baby Bottle" load before....
baby bottle: ruclips.net/video/lAG8HZzVo_g/видео.htmlsi=eU4c-vWu_ye22iFh
"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 still have a bunch of old ohmite pie wound resistors. Pie wound
I have that same VNA but mine is 75 ohms ❤. You really know your way around this machine.
I converted mine to 50ohms. ruclips.net/video/MSLm3FL7HDM/видео.htmlsi=w_mVXfZztDlHOK-3
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!
Oh, I do sort of understand why a cable is rated at 50/75 Ohms.
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.