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
This article shows use of Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) to adjust the output power of a low power transmitter.
Above, the test setup used. Continue reading VK3AQZ RF power meter (RFPM1) – adjust Tx power example
This article shows use of Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) to plot the response of a 144MHz filter.
Above, the RFPM1 as used.
Above, the test setup. The filter (DUT) is connected between a standard signal generator (SSG), and the RFPM1 connected to the filter output. A DVM recorded the DC voltage on the ‘CAL’ terminals of the RFPM1. A series of measurements was made from 140 to 148MHz and the results calculated and plotted in Excel. Continue reading VK3AQZ RF power meter (RFPM1) – filter response example
This article documents my build of Lou Destefano’s (VK3AQZ) RF Power Meter kit.
The power meter is based on probes using an AD8307 logarithmic detector.
Above, the RF Power meter with two probes. (The ferrite sleeves were not part of the kit.) Continue reading VK3AQZ RF power meter (RFPM1)
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
The subject question is often asked, and the usual responses are mindless recitals of Rules of Thumb (RoT).
In the light of the discussion at Feed line length affect on VSWR and The half waves of coax rule for measuring VSWR accurately, lets consider the subject question and develop a rational answer. Continue reading Where is the best place to measure feed point VSWR
This article explores the way in which VSWR varies along a feed line.
The graph above shows R and X, and VSWR along a feed line with a 100+j0Ω load at 3.6MHz. The feed line is Belden 8262 50Ω coax, manufacturing tolerances are taken to be zero, and the displacement is relative to the feed point, ie -ve distance is distance before the feed point, the feed point then is at the right hand side of the graph.
Continue reading Feed line length affect on VSWR
Readers of my article Galvanised steel wire OCF dipole have asked whether the analysis applies to an ordinary centre fed half wave dipole, and this answer is no, not exactly, but very close.
The current distribution on the OCF is very slightly different to a CF dipole, and this causes a very slight change in loss, 16.55W vs 16.68W.