N6THN’s novel balun – flux leakage

N6THN’s novel balun presented measurement of the Insertion VSWR of the subject balun, and N6THN’s novel balun – an explanation gave explanation that included mention of flux leakage as a contributor to the quite high inductance per unit length of the transmission line formed by the two windings.

A correspondent suggested that with a ferrite core, flux leakage is insignificant. This article calculates the coupled coils scenario.

The balun as described

Above is the ‘schematic’ of the balun. Note the entire path from rig to dipole. Continue reading N6THN’s novel balun – flux leakage

Last update: 21st April, 2021, 11:03 AM

A handy 230VAC 15A inline power meter based on an inexpensive module from eBay

This article describes a simple and inexpensive inline power meter for use as a test instrument.

CNC routing

The box cutouts were done on a CNC router, but they could be done with hand tools.

Above, calcs of feeds and speeds for the CNC router. The box is actually ABS, but cutting speed for Polycarbonate is the same.

Above is the tool path for one side of the box. The cutouts suit the 7P-2 strain reliefs. The gcode is generated from a custom Python file using a custom library of common shapes that I use. Continue reading A handy 230VAC 15A inline power meter based on an inexpensive module from eBay

Last update: 20th April, 2021, 6:16 PM

N6THN’s novel balun

One sees lots of articles and videos on how to make a current balun suited to a low VSWR antenna. This one was recommended in an online discussion on QRZ.com. N6THN might not have invented this balun, but he made a video of it.

In this case, it is described in the referenced video as part of a half wave dipole antenna where you might expect the minimum feed point VSWR to be less than 2.

Apologies for the images, some are taken from the video and they are not good… but bear with me.

The balun as described

Above is the ‘schematic’ of the balun.Note the entire path from rig to dipole. Continue reading N6THN’s novel balun

Last update: 21st April, 2021, 6:03 AM

Logging temperature meter (ltm) v1 – prototype Vin calibration

Logging temperature meter (ltm) is a ESP8266 based temperature measurement and logging device.

ESP32

The project is based on port of an existing ESP8266 Arduino project, and consideration was given to migration to the ESP32 hardware platform, but there are large differences to the WiFi related libraries… so for now, ESP8266 looks ok.

A bigger issue is that the ESP32 ADC is renowned for non-linearity, worse in some modes than others.

One poster offered the following graph of an ESP32 measurement to a discussion.

Some developers have worked on a per device look up table to implement a linearisation scheme. That means each individual device needs to have its input characteristic mapped and then used by the compensation code running on that device. Continue reading Logging temperature meter (ltm) v1 – prototype Vin calibration

Last update: 18th April, 2021, 8:48 AM

Logging temperature meter (ltm) v1 – a preview

Logging temperature meter (ltm) is a ESP8266 based temperature measurement and logging device.

The project is based on port of an existing ESP8266 Arduino project, and consideration was given to migration to the ESP32 hardware platform, but there are large differences to the WiFi related libraries… so for now, ESP8266 looks ok. There remain development options for multi channel logging if needed.

Design criteria

The design criteria are:

  • small, portable, battery powered;
  • direct reading temperature scale;
  • flexibility for a range of sensors;
  • local display including bar graph, time, and temperature;
  • log measurements to a serial port of some kind;
  • offer remote access for recent measurement log.

Algorithms

The initial algorithm implemented is for a negative temperature coefficient (NTC) thermistor using the single ADC port on the ESP8266. The code uses the Steinhart-Hart model to solve for temperature.

Above is a plot of the Steinhart-Hart model (red) and the so-called B equation (green) for the NTC used in my car. They are quite similar in this case, but the Steinhart-Hart model is more accurate. Continue reading Logging temperature meter (ltm) v1 – a preview

Last update: 15th April, 2021, 1:12 PM

Engine coolant temperature sensors – a closer look

Diagnosis of engine coolant temperature gauge issue with a certain vehicle discussed ECT sensors in a specific context.

The following table of coefficients for four common sensors was derived from published measurements by TSD of a single sensor of each type.

The so-called B equation model is \(T=\frac{1}{\frac1{T_0}+\frac1Bln\frac{R}{R_0}}\).

Part R25 B25/100
AMR3321 2246 3897
ERR2081 2218 3879
ETC8946 2450 3671
AMR1425 536 4356

These are measurements of a single sample, so average values might be a little different. Additionally, the R25 / B25/100 model is only an approximation. Continue reading Engine coolant temperature sensors – a closer look

Last update: 11th April, 2021, 1:29 PM

RK2672AM – calibration

The RK2672AM is a Chinese high voltage test set. This article describes a process for calibration of the device.

This process should not be attempted unless you have the requisite competencies, experience, tools and test equipment. There are dangerous voltages involved, so assess the hazards, plan your work, don’t attempt it if fatigued or alcohol enhanced.

Above is the front panel of the RK2672AM. Continue reading RK2672AM – calibration

Last update: 16th April, 2021, 5:04 PM

Diagnosis of engine coolant temperature gauge issue with a certain vehicle

The subject vehicle is a Land Rover Defender of mixed heritage. The owner describes the engine coolant temperature (ECT) gauge as useless.

The ECT display system is a dashboard gauge and negative temperature coefficient (NTC) thermistor mounted near the engine thermostat. It measures the engine coolant temperature (hence its name) at the hottest point in the coolant circuit… so it gives the best warning that coolant might be approaching boiling point… and which point cooling capacity catastrophically falls and there is a significant risk of permanent engine damage.

It would seem that Land Rover used many different dashboard gauges, but the underlying electrical characteristics were of just two different types. Likewise there appears to be several different sensors.

The following table of coefficients for four common sensors was derived from published measurements by TSD of a single sensor of each type.

Part R25 B25/100
AMR3321 2246 3897
ERR2081 2218 3879
ETC8946 2450 3671
AMR1425 536 4356

These are measurements of a single sample, so average values might be a little different. Additionally, the R25 / B25/100 model is only an approximation. Continue reading Diagnosis of engine coolant temperature gauge issue with a certain vehicle

Last update: 11th April, 2021, 8:32 AM