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 human 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 human 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 human 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

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

WW1WW’s matching transformer for an EFHW

At PD7MAA’s BN43-202 matching transformer for an EFHW I gave an estimate of the core loss in PD7MAA’s transformer.

An online expert questioned the analysis and later measurements, and proposed his own transformer design as evidence.

Notably, his transformer uses #61 material and a larger binocular core, a Fair-rite 2861006802 with 2t for a nominal 50Ω primary, giving loss measurements at 7MHz of 0.08dB. Note that the confidence limits of that loss measurement because of the way in which it was obtained (eg a 1% error in the 1120Ω load resistor contributes 0.043dB error to the result), but the measurements do suggest that the loss is probably very low.

Though the loss is low and Return Loss is high at 7MHz, the limits for ReturnLoss>14dB (VSWR<1.5) is 5-18MHz. With compensation, that range may be changed.

Prediction

Lets apply the method laid out at PD7MAA’s BN43-202 matching transformer for an EFHW.

The best Fair-rite data I can find quickly is a chart of the impedance of a one turn winding.

Scaling from this graph, Xs is close of 35Ω at 7MHz, so lets used that to derive some basic parameters for the core. Continue reading WW1WW’s matching transformer for an EFHW

AIM 914 produces internally inconsistent results

 

AIMuhf

A new release, AIM914 appeared recently.

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 (75Ω in this case). Continue reading AIM 914 produces internally inconsistent results

KN5L measurement of JSC 1318 windowed ladder line – MLL @ 4.2MHz

John, KN5L, published some interesting measurements he made of a recent purchase of JSC 1318 windowed ladder line. JSC Wire & Cable is now known as Seminole Wire & Cable, and this is their 1318 product.

Product with apparently similar specifications are sold by many ham retailers, they may or may not be sourced from Seminole.

Some sellers specify the % ICAS rating of the copper clad conductor, usually 30%, some just don’t mention it.

John carefully measured the DC resistance of his line section, and found that it reconciled well with the Copperweld datasheet for 21% CCS.

He also used a VNA to measure S11 of the line section with S/C and O/C terminations, and he gives links to the Touchstone files at the top of his page.

The O/C Touchstone file allows calculation of Zin. The O/C line exhibits resonance at 4.2MHz, at Zin=3.7Ω. His fuller set of measurements showed that Zo at 4.2MHz is very close to 400Ω. We can use those measurements to calculate Matched Line Loss (MLL).

Above, MLL is 0.50852dB/100m.
Continue reading KN5L measurement of JSC 1318 windowed ladder line – MLL @ 4.2MHz

Transmission line measurements – learning from failure

Introduction

A recent article questioned the accuracy of measurement of Matched Line Loss (MLL) for a modified commercial transmission line. The published results were less than half the loss of an equivalent line in air using copper conductors and lossless dielectric, when in fact there would be good reason to expect that the line modification would probably increase loss.

How do you avoid the pitfalls of using analysers and VNAs to measure line loss?

Lets walk through a simple exercise that you can try at home with a good one port analyser (or VNA). Measuring something that is totally unknown does not provide an external reference point for judging the reasonableness of the results, so will use something that is known to a fair extent,

Experiment

For this exercise, we will measure the Matched Line Loss (MLL) of a 6m length of uniform transmission line, RG58C/U cable, using an AIMUHF analyser. The AIM manual describes the method.

If you need to know the cable loss at other frequencies, enable the Return Loss display using the Setup menu and click Plot Parameters -> Return Loss and then do a regular scan of the cable over the desired frequency range with the far end of the cable open. Move the blue vertical cursor along the scan and the cable loss will be displayed on the right side of the graph for each frequency point

Note the one-way cable loss is numerically equal to one-half of the return loss. The return loss is the loss that the signal experiences in two passes, down and back along the open cable.

Our measurements will show that this is a naively simple explanation, and to take it literally as complete may lead to serious errors. Yes, it IS the equipment manual, but it is my experience that the designers of equipment, and writers of the manuals often show only a superficial knowledge of the relevant material.

Datasheet

Above is an extract of the datasheet for Belden 8262 RG58C/U type cable, our test cable should have similar characteristics. Continue reading Transmission line measurements – learning from failure

Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer – discussion of ferrite material choice

At Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer using medium µ ferrite core for receiving use – 50:200Ω I laid out a design using Fair-rite a #43 ferrite smallish binocular core. #43 is a medium permeability NiZn ferrite.

I have been asked by several correspondents why I used #43 when the consensus of online experts is that #75 is a clearly better choice for the application.

Let me say that almost all such articles and posts:

  • are absent any quantitative measurement of their proposed design;
  • they tend to use medium to large toroids; and
  • the few that expose their design calcs treat permeability as a real number that is independent of frequency.

#75 mix is a high permeability MnZn ferrite and subject to dimensional resonance in the frequency range of interest for this application, a problem exacerbated by using larger cores.

Permeability is a complex quantity that is frequency dependent and any analysis that pretends otherwise is not soundly based. Continue reading Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer – discussion of ferrite material choice