Should you trust your VSWR meter?

One often sees newbies ask about their VSWR meter readings, and a common observation is that the measured VSWR is better at low power and as power is increased, VSWR increases.

With the evolution of the ‘shack in a box’, and knowledge and experience to match, the problem is often reported observed with the transceiver’s internal VSWR meter.

Some of these ‘shack in a box’ have some pretty nifty features, for example the very popular Icom IC-7300 not only has an internal VSWR meter for the HF bands, but it can perform an assisted sweep and display the results graphically.

Isn’t that a great idea, so convenient, all good!

Or is it? Continue reading Should you trust your VSWR meter?

Co-phased collinear for 2m – discussion of phasing devices

An exploration of a cophased collinear array with coax phasing stubs explored various structures for encouraging co-phase operation of a 3/4λ vertical over perfectly conducting earth (PCE).

This article expands that set with NEC-4.2 models of some variations on the traditional Franklin form of the antenna.

Let’s start with review of the traditional Franklin form

Franklin form

The graphic above shows the topology of the Franklin form. It comprises a half wave vertical element over a quarter wave element, with a quarter wave horizontal s/c stub as the device to encourage co-phased operation of the elements. The current magnitude and phase distribution is shown in green. Continue reading Co-phased collinear for 2m – discussion of phasing devices

Motorola TAD1000B Folded Coaxial Antenna – discussion

This article is a discussion about the Motorola TAD1000B Folded Coaxial Antenna series.

Above is an image from Moto’s documentation, it shows what appears to be a simple coaxial or sleeve dipole, bit with the top quarter wave element folded like half of a folded dipole. Continue reading Motorola TAD1000B Folded Coaxial Antenna – discussion

An explanation of W5DXP’s ‘line extender device’

A correspondent wrote seeking explanation of W5DXP’s no-tuner tuner which purports to obtain a near match by adjusting the length of the transmission line using relays or switches of some kind.

The particular device that is of interest is one using a single double pole knife switch as a three position On-Off-On switch.

The accompanying explanations states that this “is a way to use a single DPDT knife switch to obtain one, two, or three feet of ladder-line depending on the position of the switch”. Continue reading An explanation of W5DXP’s ‘line extender device’

Rigexpert’s Antscope takes a bigger step backwards

At Rigexpert’s Antscope takes a step backwards I wrote of Rigexpert’s determination to cripple Antscope by reducing the maximum value of R and X on graph axes to +/- 1600Ω.

I have deferred trying the new Antscope2 until now to allow it to reach some maturity.

This article is a brief review of Antscope2 v1.0.10, brevity driven by the need to cut losses and run.

The first thing I noted is the difficulty in reading some textual data due to low contrast. The mid blue on mid grey above is very hard to read and would be even harder outdoors if measurements were being made in that environment. I did not search for alternative themes, none jumped out, but out of the box, this is very limiting. FAIL. Continue reading Rigexpert’s Antscope takes a bigger step backwards

AIM 915a produces internally inconsistent results

 

AIMuhf

AIM915 was recently pulled from the distribution site and replaced by a new release, AIM915a.

I cannot recall ever finding a new release that did not have significant defects, commonly inconsistency between displayed values. In the common theme of one step forward, two steps backwards, this version has defects that were not present in AIM910B.

This problem existed in AIM915, it persists in AIM915a.

Let’s review the internal consistency of this part of the display screen.

Most of the values given above are calculated from a single measurement value, and should be internally consistent. That measurement value is translated to different quantities, many based on the stated Zref (50Ω in this case). Continue reading AIM 915a produces internally inconsistent results

AIM 915 produces internally inconsistent results

 

AIMuhf

AIM914 was recently pulled from the distribution site and replaced by a new release, AIM915.

I cannot recall ever finding a new release that did not have significant defects, commonly inconsistency between displayed values. In the common theme of one step forward, two steps backwards, this version has defects that were not present in AIM910B.

Let’s review the internal consistency of this part of the display screen.

Most of the values given above are calculated from a single measurement value, and should be internally consistent. That measurement value is translated to different quantities, many based on the stated Zref (50Ω in this case). Continue reading AIM 915 produces internally inconsistent results

When simple explanations target a simple audience

Modern hams live busy lives and it is difficult to fit everything in to the available time / resources etc. So, there is an appetite for the skinny on some key topics, the inside info that took the wise a long time to learn.

This article discusses one of those articles containing the skinny on VSWR, What is VSWR: Voltage Standing Wave Ratio, it takes only a minute or two to read and there is a six minute video for those who prefer that.

The issues discussed here are common in the ham world explanation of VSWR and analysing them provides a learning opportunity. The video contains the issues mentioned below… and some.

Right up front, eager readers are given a take home message. If something prevents them finishing the article they have learned something they can repeat as pros. So satisfying!

In order to obtain the maximum power transfer from the source to the transmission line, or the transmission line to the load, be it a resistor, an input to another system, or an antenna, the impedance levels must match.

In other words for a 50Ω system the source or signal generator must have a source impedance of 50Ω, the transmission line must be 50Ω and so must the load

Ok, it states clearly and unequivocally that a necessary condition for maximum power transfer it that source must match line and line must match load.

We will test that proposition, but firstly the detailed explanation follows… Continue reading When simple explanations target a simple audience

Australian amateur radio licensing reform (2018)

It has become clear that ACMA intends to progress the WIA’s initial actions to partially integrate the qualifications requirement for issue of an amateur radio licence into the Australian Qualifications Framework (AQF).

The AQF is the national policy for regulated qualifications in  Australian education and training. It incorporates the qualifications from each education and training sector into a single comprehensive national qualifications framework. The AQF was introduced in 1995 to underpin the national system of qualifications in Australia encompassing higher education, vocational education and training and schools.

That push on integration includes the use of Registered Training Organisations (RTO) for assessments, RTOs are an element of the Vocational Education and Training Sector (VETS).

The definition of Vocational Education and Training can be taken from australia.gov.au:

Vocational education and training

Designed to deliver workplace-specific skills and knowledge, vocational education and training (VET) covers a wide range of careers and industries, including trade and office work, retail, hospitality and technology.

So, the WIA and ACMA have over a couple of decades acted to integrate amateur radio qualifications in the AQF to some extent, and current actions are intended to perform assessments within the VETS (ie by VETS qualified assessors under an RTO). Continue reading Australian amateur radio licensing reform (2018)