Having a few nice vintage shortwave radios around, I decided it would be nice to actually USE the dang things once in a while 🙂  And given the almost unusably noisy performance of indoor short wire antennas, I made some loop antennas to cover approx 3 – 18 MHz to see if performance could be enhanced.
Continue reading Dual-Band X-Frame Shortwave RX Loop
4,069 total views, 5 views today
First cut at an Excel spread sheet to analyze a small RX loop’s noise and frequency response performance.
Continue reading Small RX Loop Analysis – An Excel Sheet – Fields, Voltages, Noise Levels…
2,070 total views, no views today
You may have wondered why some of us keep yammering on regarding “Common Mode Current” on the coax, and why common-mode prone designs (like end-feds and JPoles) are so problematic. Here’s an example of a 915 MHz antenna for a wideband comm system prototype I am designing. I decided on a wide-band vertical dipole.
In the pix below, we see the dipole front, and the dipole rear in it’s final form (sans heat shrink) – with a single loop binocular type 61 core performing the 1:1 current BalUn / choke function (they are the same thing):
Continue reading Why We Don’t Like Unintended Common-Mode Current Flow On Our Transmission Lines
2,308 total views, 1 views today
Apparently there are lot’s of differing opinions on antennas – now there’s a shocker 
 Hopefully, we can put some rough numbers on things to help folks to figure out where opinion ends and basic principle begins.
Continue reading Low Gain Ground Mounted Antennas for LEO Satellites
6,398 total views, 1 views today
Often one sees characterization and loss measurement of UNUNs using an SWR measurement of the UNUN when terminated in it’s transformation resistance, or with the “back-to-back” 2-x-Loss method. Each method reveals something about some quality of the UNUN, but neither method tell us much about how much power the UNUN will deliver to the actual antenna.
In this article I will show a simple method of measuring actual UNUN losses into the actual load impedances that the UNUN will see in service.
Continue reading “Z-Substitution” Method for Measuring UNUN Loss Into Real-World Load Impedances
4,715 total views, no views today
Excellent technical article regarding limited space antennas:
Continue reading Classic W8JI Limited Space Antennas Article
3,172 total views, no views today
I modeled a number of shortened dipoles with various capacitive hats at their ends. I think the results may interest you.
Continue reading Article by SP3L Modeling Various Configurations of Capacitance-Hat Dipoles
2,361 total views, no views today
In this article we look at the reduction in feedline loss when we use a BMU to mitigate impedance extremes at the base feedpoint of a Vertical or Inverted-L antenna. Naturally, these antennas are worked against a proper counterpoise radial system for decent efficiency, especially on the low bands.
We look at the cases of a 42 ft antenna, and use an average of the measured and modeled feedpoint impedance to calculate feedline losses* for 50 ft of RG8x and for 100 ft LMR400.
The BMU referred to here is:
A 9:1 UNUN for the mid and high bands
A Loading Coil, switched in instead of the UNUN, for the low bands
Continue reading Why we use a Base Matching Unit (BMU) with End/Base-Fed Verticals and Inverted-Ls
4,526 total views, no views today
We look at the magnitude of the impedance of an EFHW “antenna” for short counterpoise lengths.
Thanks to Jon AF7TS for the suggestion and discussions that led to this article.
In engineering we sometimes can not directly calculate a value, often when a “divide-by-zero” shows up, as when we try to calculate an impedance wiith a zero length element. However we can usually still tell what that value will be by sneaking up next to it and determining what it asymptotically approaches.
Continue reading Z of EFHW vs. “Counterpoise” Length
10,901 total views, 1 views today
A simple transmitter, transmission line, and an “End-Fed” antenna WITHOUT a formal “Counterpoise” – We add a loss-less choke at the feedpoint, tune out it’s inductance with a capacitor, and see why common-mode current on the coax shield is the SAME as without the choke.
From Part 1 and Part 2 of the “Current Flow Fundamentals for an “End-Fed” articles, we saw that common-mode current must always flow on the coax shield when we don’t use a formal counterpoise. And that the value of current on the “counterpoise” is identical to that on the “radiator” at the feedpoint.
In Part 3 we saw that it doesn’t matter what loss-less device(s) we put at the feedpoint – when we re-adjust our transmitter or tuner the SAME current flows common-mode on the shield as before.
Continue reading Current Flow Example for an “End-Fed” Antenna with a Loss-Less Choke
5,375 total views, no views today
