Current Flow Fundamentals for an “End-Fed” Antenna – part 3

Part 3 – We place various devices at the feedpoint of an “End-Fed” antenna without a formal “Counterpoise” – We will see why the SAME common-mode current must ALWAYS flow on the coax shield just as in Part 1.

The typical “end-fed” generally has an impedance greatly different from 50 ohms, so it is rarely fed directly with coax, as losses on the transmission line will be undesirably high for lengths of coax greater than a few 10’s of meters.

Note the high loss on several bands when a 42 ft “end-fed” is directly fed with 50 ft of RG8x coax (yellow bars)* ===>

cableloss_unun-vs_direct_feed Continue reading Current Flow Fundamentals for an “End-Fed” Antenna – part 3

3,038 total views, 2 views today

Please follow and like us:

Verticals and Inverted-Ls for the Low Bands – Horizontal Antennas for High Bands

Ever wonder why successful DX-seeking stations so often use vertically polarized Verticals or Inverted-Ls on those lower bands?  And why horizontal dipole-type antennas are most often seen for use on the higher shortwave bands?  Even loop designs, intended for DX chasing on these lower bands, most often employ vertical polarization.

There’s good solid technical reason for this old adage:

If you can’t get a horizontal antenna up around 3/8 wavelength or higher, then use a vertically polarized antenna.

Continue reading Verticals and Inverted-Ls for the Low Bands – Horizontal Antennas for High Bands

5,468 total views, no views today

Please follow and like us:

Current Flow Fundamentals for an “End-Fed” Antenna – part 2

Part 2 – A 40 Meter EFHW with a “Radiator” wire and various length “Coax-as-Counterpoise” wires is analyzed – We will see that the common-mode current is almost always LARGER on the coax shield some distance away from the feedpoint, which is why the “counterpoise” radiates and is called “the other half of the antenna”.

It is sometimes said that common mode current flow on the coax shield of an “End-Fed” antenna system is everywhere low,  simply because the feedpoint current is relatively low.  This is claimed even for systems with no “counterpoise”.  In this article we will see that this is not true.

…charge conservation is the principle that electric charge can neither be created nor destroyed.”*

As shown in Part 1, from this perfectly reasonable principle we now know that there are NO 1-Terminal RF power sources!

nooneterminalacsources2 Terminals – YES!            1 Terminal – NO!

Continue reading Current Flow Fundamentals for an “End-Fed” Antenna – part 2

2,935 total views, no views today

Please follow and like us:

Classic G3TXQ Balun / Choke Article

Excellent technical reference article by Steve G3TXQ:

choke_impedances_g3txq

Amateur Radio (G3TXQ) – Common-mode chokes

The above chart presents the results of impedance measurements made on a variety of common-mode choke implementations across the frequency range 1MHz to 30MHz. Amateur frequency allocations are indicated approximately by the vertical grey bands. Continue reading Classic G3TXQ Balun / Choke Article

4,031 total views, no views today

Please follow and like us:

Classic N6LF Radiation Resistance Article Series

rr-study-appendix-a-1 pdf

rr-study-appendix-b-v2-1 pdf

rr-study-appendix-c-rev-1-1 pdf

rr-study-appendix-d-1 pdf

   rr_study_n6lf

 

from http://from http://rudys.typepad.com/

 

672 total views, no views today

Please follow and like us: