Most of the time the requirement is for listing by a "Nationally Recognized Testing Laboratory" of which UL is but one. For instance Los Angeles county requires that any electrical equipment sold be
Excellent.. How did you find that page? I searched "497" on their site and got just fiber optics. They have a page dedicated to them, but the associated PDF is probably easier to work with: https
Enlarging on this a bit - They are all examples of charging by particles hitting or coming near something. Whether it's wind blown dust, snow, or ice, or raindrops, etc. And whether the charge got
FWIW This is where a lot of the confusion about "charge dissipators" (porcupines, for example) for lighting reduction comes from. This is an excellent explanation, Jim. I was hoping you would c
The idea being that you're feeding with 120 ohm twisted pair rather than 75 ohm coax? I have been expanding my RX system to include more Beverages fed with CAT6 rather than RG-6. In this video I de
Something else to consider is whether the limit is "no appreciable effect" or "some damage" or "catastrophic failure". Hams can usually tolerate some damage, as long as nobody gets hurt and no stru
Actually, what you do is run the feedline up through the bottom element (which is a tube). And then choke it at the bottom of that element. It makes what's also called a "sleeve dipole" And yes,
Yeah, the pattern doesn't change much with the physical length of the dipole/monopole, if it's < 1/2 wavelength. There's a slight difference in "efficiency" (defined as how much power gets radiated v
And these days, with inexpensive auto match boxes - that gives you a lot of "field flexibility" Throw it up, and who cares if it happens to be resonant at 6.9 MHz instead of 7.1 - the tuner losses wi
Yeah.. HFTA sort of builds on Jim Breakall (WA3FET) papers on propagation modeling - modeling the terrain as a series of parallel plates at different angles. Sticking with H pol makes the calculat
This, exactly. There are people making measurements with drones - for instance, the pattern of the 9 MHz antenna on Europa Clipper was measured with a drone (and with scale models on a conventional
If you're spending millions of dollars on a system that depends on HF propagation (or lack thereof) or trying to understand the physics of the ionosphere, then the tools are pretty handy. Practical e
Yep - FEKO is one of several. Unless your hobby/job is modeling, though, I believe most folks would come to the same conclusion. (and still free, although I think it's a web based version now htt
I would love to have a globe that displayed propagation on the surface. (Yes, I know you can do it on a flat panel with any number of tools) At JPL we have a big (>1 m diameter) spherical glowing
The commercial devices use a projector and a fancy lens/mirror to make a full sphere image That way you can project a basemap (i.e a picture of the Earth) with overlays - the one here is fairly fanc
I'm in the middle of testing a scheme at work where we use 3 RTL-SDRs and a RPi with 3 whip antennas at 90 degrees from each other. If all you want is amplitude, that's all you need. If you want pha
Well, this is sort of what folks are trying to do with various metrics that attempt to weight things. It's tricky, because we (very inclusive we for all users of antennas) like to have some sort of
The tolerances on inductors wound on toroids (even the special #31 mix) are surprisingly wide for people used to buying components with 1% or 5% tolerances as a matter of course - weve gotten spoile
I would think the port 2 (labeled Ch1) on nanoVNA and nanoVNA derived would be pretty close to 50 ohms - its a ~17 dB pad. And Port 1 (labeled Ch0) is a resistive bridge - so its impedance is slight
This is where tools like the NanoVNA are really nice - you can calibrate at the end of the coax. Or, if you've measured the coax once, you can save it, and post process your data in one of the apps