Photo Voltaic Array – unbelievable efficiency from Chinese sellers

A friend recently purchased one of the many PV arrays advertised on eBay only to be disappointed.

A common metric used to evaluate cell technologies is conversion efficiency with 1000W/m^2 insolation. Most popular products are monocrystalline silicon technology which achieves 18-25% efficiency on an assumed 1000W/m^2 insolation.

If we look carefully at the above panel advertised as 200W, the active PV area is less than the frame size, probably \(A=0.93 \cdot 0.63=0.59 m^2\). We can calculate efficiency \(\eta=\frac{p_{out}}{1000 A}=\frac{200}{1000 \cdot 0.59}=34\%\), nearly double expected efficiency for monocrystalline cells. Continue reading Photo Voltaic Array – unbelievable efficiency from Chinese sellers

A dipole centre insulator from HDPE cutting board

I made a small dipole centre insulator from 10mm HDPE cutting board on the CNC router. HDPE is moderately UV resistant so should survive for some years outdoors.

The insulator is 100mm across its widest points. No provision is made for supporting coax, it is for use with home made open wire line which will fall from the dipole leg ends. If you want to use it with coax or ribbon feedline, then incorporate a tab to secure those lines.

Continue reading A dipole centre insulator from HDPE cutting board

Windows 10 – sound device Signal Enhancements

Recent versions of Windows 10 have made changes to some audio input processing.

Above is a screenshot of a Microphone Properties window, and attention is drawn to the section highlighted in pink which may appear in some devices.

The Signal Enhancements would appear to introduce certain non-linear behaviour.

I preface this with saying the ‘enhancements’ are probably hardware dependent (ie the chipset used and driver capability) but may also include Windows core, and this report applies to my specific configuration but hints issues that may be systemic.

That said, I performed a simple test switching an audio sine generator between two close frequencies and observed the level vs time in SpectrumLab.

The lower part of the screen is with ‘enhancement’ ON, the only change in the upper part is with ‘enhancement’ OFF. Continue reading Windows 10 – sound device Signal Enhancements

nanoVNA – experts on improvised fixtures

A newbie wanting to measure a CB (27MHz) antenna with a UHF plug when his nanoVNA has an SMA connector sought advice of the collected experts on groups.io.

One expert advised that 100mm wire clip leads would work just fine. Another expert expanded on that with When lengths approach 1/20 of a wavelength in free space, you should consider and use more rigorous connections.

At Antenna analyser – what if the device under test does not have a coax plug on it? I discussed using clip leads and estimated for those shown that they behaved like a transmission line segment with Zo=200Ω and vf=0.8. Continue reading nanoVNA – experts on improvised fixtures

Simsmith bimetal line type – revision #1

This article is a revision of an article Simsmith bimetal line type for Simsmith v17.2 and revisions to my own model for current distribution in a conductor.

This article discusses various measurements and models of Wireman 551 windowed ladder line, including adapting Simsmith’s bimetal line type to bear on the problem.

Measurements

A starting point for characterising the matched line loss (MLL) of the very popular Wireman 551 (W551) windowed ladder line is the extrapolation of measurements by (Stewart 1999) to 1.8MHz. Since the measurements were made at and above 50MHz where the W551 has copper like performance, this is likely to underestimate actual MLL and such wide extrapolation introduces its own uncertainty. Nevertheless, the datapoint is MLL=0.00227dB/m.

This is a revision of an article written in Feb 2020, capturing revision of Simsmith to v17.2 and revision of my own current distribution model.

Dan Maquire recently posted a chart summarising measurements of these lines.

For the purposes of this article, let’s tabulate the MLL at 1.8MHz in dB/m. Continue reading Simsmith bimetal line type – revision #1

A model of current distribution in copper clad steel conductors at RF – capturing conductor curvature

A model of current distribution in copper clad steel conductors at RF laid out a model for current distribution, though ignoring curvature of the conductor in calculating current density vs depth.

A model for current distribution in a conductor is that for a homogenous conducting half space with surface current parallel to the interface. Current density at depth d is given by the expression \(J_r=J_R\frac{J_0(kr)}{J_0(kR)}\) where δ is the skin depth \(δ=(ω \cdot µ \cdot σ)^{0.5}\) and \(k=\frac{1-\jmath}{\delta}\), σ is the conductivity). This takes into account curvature of the conductor surface, albeit with slower compute time.

Let’s compare the two algorithms on a test case at 1.8MHz being copper cladding of 67µm copper over a steel core for an overall diameter of 1.024mm (#18).

Above is a stacked image, the simpler algorithm is the feint plot.

There is a quite small difference in this case. When the expected loss of 400Ω line using the conductor is calculated, the result with the simpler algorithm is 1.3% less than the later one using the Bessel distribution.

Distance to fault in submarine telegraph cables ca 1871 – the leap expanded

Distance to fault in submarine telegraph cables ca 1871 gave a mathematical explanation of the location of fault…

Now it is in terms of the three known values u,v,w and unknown x.

\(w(v-2x+u)=(v-2x+u)x+(v-x)(u-x)\\\)

\(x^2-2wx+vw+uw-uv=0\) from which you can find the roots.

\(x=w – \sqrt{(w-v)(w-u)}\\\)

I have been asked to expand the last ‘leap’.

So we have \(x^2-2wx+vw+uw-uv=0\) which is a quadratic, a polynomial of order 2.

The solution or roots of a quadratic \(ax^2+bx+c=0\) are given by \(x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}\).

So, for our quadratic \(a=1, b=-2w,c=vw+uw-uv\), so \(x=\frac{2w \pm \sqrt{(2w)^2-4(vw+uw-uv)}}{2}\).

Dividing the top and bottom by 2 we get \(x=w \pm \sqrt{w^2-(vw+uw-uv)}\) which can be rewritten as \(x=w \pm \sqrt{(w-v)(w-u)}\).

We want the lesser square root \(x_-=w-\sqrt{(w-v)(w-u)}\) because x must be less than w, a constraint of the physical problem.

So when measurements gave \(v=1040 \Omega\) and \(w=970 \Omega\) we can calculate that the distance to fault is the lesser root, 210.3km from Newbiggen-by-the-sea. (The greater root would imply a -ve value for x or y which is not physically possible.)

Review of MXITA SMA-8

The MXITA SMA-8 is a low cost torque wrench for 8mm, specifically for SMA connectors. It has an adjustable calibration, supplied at 1Nm but easily adjusted down to 0.6Nm to suit common brass SMA connectors, especially of doubtful quality.

I bought this after seeing several recommendations on a nanoVNA forum.

Above is the factory pic of the SMA-8. Continue reading Review of MXITA SMA-8

Distance to fault in submarine telegraph cables ca 1871

In the early days of submarine telegraph cables, the cable technology was a single core steel wire wrapped in gutta-percha worked against ground. Now the gutta-percha was not a uniform or durable insulation and leaks to ground (sea) were inevitable, and when the leakage became sufficient the cable could not longer be used and had to be repaired.

The earliest method of locating a cable fault was a binary chop… which would mean deploying a cable ship, grapnelling for the cable, hauling it to the surface with a special dividing cut and hold grapnel that severed the cable when tension was too great, buoying off one end and steaming back to the other to haul it on board, clean it up and test to the far cable station. New cable was spliced and the cable ship steamed back to find the buoy and pull that end on board, clean and test to the other end. This was done to localise the fault, and eventually replace a fault section of cable. During this longish period, the cable was out of service. Continue reading Distance to fault in submarine telegraph cables ca 1871