"Horizontal antennas care NOTHING about soil quality but EVERYTHING about height." I often use this notion myself, but it is a simplification. It is not true in general. Some time ago I was surprised
"Now, reading that Brian had started it all, perhaps he might take it on." TA, the terrain analysis program I wrote in the 1990s, handled vertical as well as horizontal polarization. I went to some e
"...nothing we do can change the effect that the ground has on takeoff angle." Nothing we yet know about. I don't believe I'm the only one who has spent some effort trying to find a way to achieve lo
"Any thoughts on this text fixture?" Dave, use the Y21 method instead of the conventional S21 method to suppress any shunt capacitance in the test fixture. This S-parameter plotter implements both me
"It looks like the Y21 method is a bit better, especially with increasing frequency, but the S21 is a decent proxy as is mentioned on the web page article already." Whether the Y21 method is needed d
"Brian, would you consider the N2PK VNA in the "fancy" category rearding your calibration comment?" Jeff, I don't think the N2PK measures all four S-Parameters nor does it do a 12-term calibration. I
One last thing. Common-mode choke impedance is sensitive to capacitance across the choke. (The Y21 method suppresses shunt port capacitance, not port-to-port capacitance.) Proximity to anything condu
"The N2PK is fully capable of 12-term calibration..." Thanks for setting me straight, Gary. Measurement of the choke and the feedline at the point of installation lets you calculates the benefit of a
"A first approximation of the effectiveness of a choke in a specific installation can be computed in NEC by adding a resistive load equal to the resistive choking Z to the model, which includes the f
"At HF frequencies, Id be surprised of the Z is far off. (But I can measure it I have two NanoVNAs - Ill do that later today)" Jim, I'd be interested in what you measure. Port 1 for N6LF's NanoVNA-H4
This plot shows how the conventional S21 method can overestimate the resistive part of common-mode choke impedance: https://i.postimg.cc/fy30Qk3f/R.png The Y21 method can plot the shunt capacitance a
"(the process is useless if you only do it in one spot since as you say it could be a current minimum)" But the shield may have a traveling wave, either due to radiation or nearby lossy objects, the
...I assume that we want to place the CMC as close to a current maximum as we can..." In the models I've looked at, that's invariably at the feedpoint. If you still have CM issues after installing a
I went through the dozen or so .s2p files I have for common-mode chokes. The error due to shunt port capacitance was most often restricted to the resistive and reactive parts of the measured impedanc
"Any thoughts on this text fixture?" Dave, I completely forgot that I had contacted Halibut Electronics, the fixture manufacturer, a couple years ago. Mark Smith sent me two .s2p files and photos of
Bob Larkin, W7PUA, has developed a tiny ground probe that offers several advantages over larger probes when measuring local ground constants. It can provide artifact-free data to 100 MHz, it is easy
"what would be interesting is a probe design that doesn't require penetrating the surface (e.g. I could put it on my concrete driveway)" Jim, here is an interesting survey of the many ways to measure
"What is usually used is the 'Slingram method'." Thanks for mentioning this, Tor. Quite a bit of research seems to have been done on the method. A good search term for HF devices is HFEMI sensor Here
"I've downloaded the map (which is in pdf segments) to my website." That map is for the AM broadcast band. It is not valid at HF. https://k6sti.neocities.org/hfgc Brian ______________________________
"...I'd be most interested in trying to determine how deep the equivalent RF ground is for future modeling (because it certainly isn't at the surface of my dry Arizona hillside)..." Dave, the RF grou