Category: Antennas

NEC-2 and NEC-4 support a GM card to translate and rotate a structure in three dimensions.

This article gives a simple but practical example of exploitation of this often overlooked facility. Continue reading Exploitation of NEC’s GM card

I have a bit of a soft spot for the Diamond X-50N. It is a fairly rugged vertical for 2m/70cm. Though I live in a rural setting, I resist the temptation of high gain antennas of this type as they tend to suffer fatigue problems resulting in noise in quick time, whereas the rigid one piece X-50 seems to last and last (I have another that must have had 25 years outdoor service).

The X-50N is mounted on a telescopic steel mast at 11m at its base, and fed with 10m of LDF4-50A to the antenna entrance panel, and 2m of LMR-400 to the radio. The XN50N has three short radials which are visible in the pic above, but somewhat obscured by a fan of four upwards pointing wires to discourage birds perching on the gibbet for the G5RV. Continue reading Diamond X-50N #2 at VK2OMD

My friend Richard found himself located on the margins of coverage of the local 2m repeater where multi path reception was the main problem, a but a little lift in signal would also help.

This begs a small Yagi solution. Continue reading A compact 3 element Yagi for 2m

A reader of my article Are gamma matches as bad as all that asked whether the W5VJB dipole was a gamma match given the hint in the article that the traditional gamma tuning capacitor is not essential to a gamma matched antenna.

Above (Britain 2006) is the subject dipole which Britain describes as a partial folded element having a J shape which is grounded at the midpoint of the longest portion of the element. ((Duffy2010b) refers to it as a half folded half wave dipole.)
Continue reading Is the W5VJB J dipole novel

Seeing the comment recent online comment about a gamma match as I have noted from research online, NEC does not support modelling of the match component reminds one of the unreliability of online sources. This appeal to non-authority is fallacious, this writer writes as if it is fact that NEC does not support modelling a gamma match, and that is quite wrong.

NEC has limitations on geometry elements relative to each other and to wavelength, and those apply not just to the gamma match, but the entire model. It is the modeller’s challenge to stay within those limitations.

This article documents an NEC model of a real antenna and the model reconciles with the real antenna. Continue reading Are gamma matches as bad as all that