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
Lots of hams recite a rule that accurate measurement of VSWR can only be made at the feed point or an integral number of electrical half waves from the feed point.
It is one of those ‘rules’ that the proponents cannot usually explain… they would regard themselves as experts, but blindly follow folk-lore that they do not understand. Continue reading The half waves of coax rule for measuring VSWR accurately
In a recent posting on VKLOGGER, I posted the graph below of licence trends to Jun 2013.
VK3HZ commented at Re: Amateur population trends – 2013:
I wonder who it really was who first said “Lies, damned lies and statistics”?
I’m surprised any conclusions can be reached based on the data presented:
– the last point on the graph totally influences the outcome. Take that point away and there’s quite a different (rising) trend line.
– Is this final point influenced by some other effects (e.g. changes or delays in license processing …)?
– why should a second-order polonomial be used to model number of licenses vs. time? Why does it have to have a turning point?
– the vertical axis is greatly expanded, over-emphasising visually any noise on the data
– if the same analysis had been done after the 2007 data had been released, the trend would be even more disastrous. However, reality was much different.
So, I don’t (yet) believe the sky is falling.
I will respond here as I now refrain from posting on VKLOGGER. Continue reading A response to VK3HZ’s comment on amateur licence trends
This is a 2014 update of an article written originally in October 2005, earlier editions published on VK1OD.net which is now offline.
Over recent years to 2002, the number of issued amateur licences was declining, the trend was about 2.8% pa decline over the five years to 2002.
This has concerned some people, who took the view that the decline was a harbinger of the impending demise of Amateur Radio. Continue reading Australian amateur population trends 1998 – 2014
VK2XSO posted a sweep of “Return Loss (SWR) (the lower plot) from 500 to 2500MHz of a 50Ω load through ~5m of RG59” apparently to demonstrate his knowledge of transmission line basics. As he says “here are also many other things we can deduce from looking at these two lines.”
For students of transmission lines, some deductions… Continue reading Exploring VK2XSO’s transmission line example
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
A reader of Why the preference for Guanella 1:1 current baluns for HF wire antennas asked if a similar model can be built for a Ruthroff 4:1 balun.
Hams tend to insist that the Ruthroff 4:1 balun cannot be represented by transmission line elements, but they are quite wrong. Continue reading A SPICE model for a Ruthroff 4:1 balun.
I am often asked why I recommend a Guanella 1:1 balun with high choking impedance for most HF wire antennas over voltage baluns and 4:1 current baluns. This article explores the topic using SPICE models for a voltage balun, 1:1 current balun, and 4:1 current balun. Continue reading Why the preference for Guanella 1:1 current baluns for HF wire antennas