Battery contact corrosion on digital calipers

Corrosion of battery contacts in all manner of things due to leakage from the batteries is a growing problem as we seem to accumulate more and more devices that contain batteries and it becomes a chore to replace batteries by their expiry date.

Replacing batteries by their expiry date does not guarantee freedom from leakage related corrosion. The battery market is flooded with counterfeit product and it is hard to know what is genuine, even from apparently reputable suppliers.

Above is a cheap Chinese digital caliper that was damaged by leakage from a brand name (Duracell) SR44 cell. The characteristic green residue has been cleaned from the positive contact with an alcohol soaked cotton bud, and then the contact scratched with a Burgeon 2834C fibre glass scratch brush (below) to remove remaining corrosion products whilst vacuuming to extract as much of the residue as possible. Again, a wipe with a clean alcohol soaked cotton but leaves the contact as clean as practicable. These scratch brushes are extremely effective, one needs to avoid over use which removes more plating than desirable. Continue reading Battery contact corrosion on digital calipers

Working a common mode scenario – VK2OMD – voltage balun solution

Recent articles Working a common mode scenario – G3TXQ Radcom May 2015 and Working a common mode scenario – G3TXQ Radcom May 2015 – voltage balun solution analysed a three terminal equivalent circuit for G3TXQ’s antenna system based on his measurements. Solutions were offered for the expected common mode current with no balun, with a medium impedance common mode choke (current balun) and an ideal voltage balun.

In summary, though G3TXQ expected the antenna system to have good balance, on measurement it was not all that good. The analysis showed that even a moderate impedance common mode choke reduced the common mode current Icm substantially more than no balun, or an ideal voltage balun.

This article performs similar analysis of the case of an ideal voltage balun applied to my own antenna system documented at Equivalent circuit of an antenna system at 3.6MHz.

In this article I will use notation consistent with (Schmidt nd).

Above is the equivalent circuit. Continue reading Working a common mode scenario – VK2OMD – voltage balun solution

Working a common mode scenario – G3TXQ Radcom May 2015 – voltage balun solution

At (Hunt 2015) G3TXQ gave some measurements of his ‘balanced’ antenna system.

Above is Hunt’s equivalent circuit of his antenna system and transmitter. It is along the lines of (Schmidt nd) with different notation. Continue reading Working a common mode scenario – G3TXQ Radcom May 2015 – voltage balun solution

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

Sydney harbour is a beautiful place

One of the trips I am known to take is to Manly for lunch.

Above is a pic taken whilst waiting for the train home at Circular Quay. On the right is the ferry Freshwater arriving from Manly. The Opera House is just visible on the right north of the ‘toaster’ (one of the eyesores on the harbour).

It was a sparkling day on the harbour (Port Jackson) which bought back memories of many happy days boating and sailing, it is a beautiful waterway.

Manly is about 30min north east, 12km over the water, just on the north side of Sydney heads.

It is challenging to get pics on the ferry as tourists push their phone in front of your face to take videos, 5 to 10 minutes as a time.

Above, the route is from home to Bowral station by car, diesel train (Endeavor railcar) to Central, electric train on the Sydney underground to Circular Quay, and ferry to Manly. The return journey was similar but electric train from Circular Quay to Campbelltown then diesel train to Bowral. The round trip is just on 300km and nearly three hours for each direction of travel.

An interactive zoomable map is available. Zooming in around Sydney and a little south will show track jumps due to underground rail.

The track was captured with a Holux RCV-3000 GPS logger, logs downloaded with BT747 (Chinese firm Holux is defunct and so is their application which is now locked out of its maps provider).

Leaflet / OpenStreetMap map rendering on devices with tiny pixels

I wrote an application that presents maps on a webpage using Leaflet and OpenStreetMaps, and some readers commented that the text was hard to read on their devices.

It turns out that this issue seems present on devices with high resolution small screen (ie high pixels/mm or small pixel size).

The reports raise the question of whether it is the compatibility of the device and the user’s Visual Accuity (VA).

VA is often assessed on the familiar Snellen chart which has characters of a 5×5 grid and normal vision is indicated by reading characters that subtend 5 minutes of arc (MOA), or 1MOA for each ‘pixel’ (px).

An example phone screen calculation

My Huawei dub-lx2 has a screen height of 1520 px and 144mm, so the px size is 95µm. Keep in mind that the size of this pic may be much smaller on the phone that on your viewing device. Continue reading Leaflet / OpenStreetMap map rendering on devices with tiny pixels