Should you trust your VSWR meter – linearisation

Should you trust your VSWR meter? asked an interesting question, and Should you trust your VSWR meter – detector linearity discussed a problem apparent in may VSWR meters.

This article illustrates one method of linearisation of the detector response of a practical VSWR meter.

Radio-kits SWR meter

This article contains an analysis of the analogue circuitry of the Radio-kits SWR meter.

The directional coupler at top left contains half wave peak detectors for forward and reflected waves. They are wired to the two compensated op amps at lower right (the connections are not shown on the circuit as the coupler may be remote, follow the terminal designations). Continue reading Should you trust your VSWR meter – linearisation

T962 IR reflow oven rework #2

T962 IR reflow oven rework documented rework of the inexpensive T962 IR rework oven. This article reports some tests on various modules.

The solder cream used is cheap Chinese 63/37 tin/lead solder cream that has been in the fridge for a couple of years, so it is past its use by date.

Solder cream was applied to pads using a pneumatic drive of a 10ml syringe with #22 blunt needle.

A U shaped piece of 0.5mm copper wire was placed on the oven drawer tray and the boards placed on the wire. This to isolate the boards from the thermal mass of the drawer tray.

The program used is shown above. Continue reading T962 IR reflow oven rework #2

Should you trust your VSWR meter – detector linearity

Should you trust your VSWR meter? asked an interesting question, and based on experience, including a relevant example, concluded:

The answer is no, like any measurement instrument, prove that it is trustworthy in the intended application.

It went on to ask:

If the VSWR meter is designed to fail, why does it fail?

This article contains an analysis of the analogue circuitry of the IC-7300 directional coupler to explain the likely cause of its poor behaviour.

IC-7300 directional coupler schematic


Above is an extract of the IC-7300 circuit in the area of the directional power coupler used for VSWR measurement. The circuit is a quite conventional Bruene coupler, and its response is similar to several types of directional couplers that produce a DC output voltage from a half wave detector. Continue reading Should you trust your VSWR meter – detector linearity

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

A second test of the FA-VA5 antenna analyser

I recently acquired a FA-VA5 antenna analyser.

Whilst preparing A first test of the FA-VA5 antenna analyser, issues were noticed with the user interface design / implementation.

This article started off as a video demonstration of measuring the Matched Line Loss (MLL) of a 6m length of old / budget grade RG58CU for comparison with the datasheet.

Using the instrument was such a frustration due to the user interface design / implementation, but more time was devoted to trying to understand it and experimenting with button press timing etc… but I must admit, to no avail. I persevered and made the measurements which are reported here, the matter of the interface issues will be dealt with separately.

So, the interpolated datasheet MLL for quality cable, Belden 8262 (RG58C/U), is 0.319dB.

The measurement technique is the measure the ReturnLoss of the DUT with o/c and s/c terminations, and estimate MLL=(RLo+RLs)/4.

Above, the o/c test. Continue reading A second test of the FA-VA5 antenna analyser

A first test of the FA-VA5 antenna analyser

I recently acquired a FA-VA5 antenna analyser.

The analyser is a low cost kit (~A$265 including high accuracy cal kit and postage), the SM components are already fitted to the PCB, but the other components like switches, display connector etc need to be fitted. Whilst these parts are hand soldered, some pins are quite close to other components and require a fine soldering tip and steady hand. It is probably an hour’s work to complete the assembly.

Above is the completed FA-VA5. As can be seen, it has just three buttons which are used to navigate a menu system and to perform data entry, both of which can be a bit tedious but that is the trade off for a simple user interface.

This article is not a wide ranging review, it is a first test on a component that it relevant to the HF ham experience, and is challenging for most analysers in common use. Continue reading A first test of the FA-VA5 antenna analyser

Arduino SAMD21 bootloader protection II

At IoT – exploration of LoRaWAN – part 2 I reported some quality issues with two low cost SAMD21 Arduino Zero like boards, and at Arduino SAMD21 bootloader protection some related discussion.

In view of continuing experience of incorrectly programmed low cost SAMD21 boards, I have decided to re-flash them as a matter of course

Above is one of the culprit boards. Continue reading Arduino SAMD21 bootloader protection II

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