A correspondent asked for an explanation of a novel balun described in Radcom Feb 2019 by K3MT.
Above is a diagram of the so-called “cable balun”.
To evaluate it, I have inserted it into one of the NEC models used for the article Baluns in antenna systems, the model used for Model 3 which I will repeat here for convenience. Continue reading Radcom Feb 2019 “cable balun”
Elecraft produces a directional coupler that may interest QRP aficionados. It comes with instructions for 20dB and 30dB coupling factors rated at 25 and 250W respectively from 1 to 30MHz.
This article reviews the magnetics design of the -20dB / 25W coupler.
The coupler uses a type of Sontheimer coupler (Sontheimer 1966) and these are commonly poorly designed. The first question is whether the magnetising impedance of T2 which appears in shunt with the load is sufficiently high to not give rise to poor insertion VSWR. Continue reading Elecraft CP-1 directional coupler – magnetics review
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.
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
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.
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
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?
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
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
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
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’
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
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