Electronics – Page 22 – owenduffy.net

Vacuum capacitors – construction implications for Q

Vacuum capacitors are used for high end applications that require high voltage withstand and low loss.

Though they are called capacitors, and simple analyses treat them as a capacitance with some small equivalent series resistance (ESR), there is more to it.

Above is a view (courtesy of N4MQ) looking into one side of a vacuum capacitor. It consists of an outer cup, and a series of 5 inner cups progressively smaller in diameter. The other side of the capacitor has a similar structure but the cups site in the middle of the spaces between cups in the first side.
Continue reading Vacuum capacitors – construction implications for Q

Last update: 19th January, 2018, 9:38 AM

60dBm.com 0.1-3000MHz Return Loss Bridge

This article is an expose of the internals of a 60dbm.com 0.1-3000MHz Return Loss Bridge available on eBay for around $17 incl post.

Above, the 60dbm.com Return Loss Bridge. Continue reading 60dBm.com 0.1-3000MHz Return Loss Bridge

Last update: 20th November, 2019, 6:31 AM

A comparo of two bare light dimmer modules

Two bare dimmer modules sold on eBay with identical specification and similar price are compared.

Both claim to have zero hysteresis. Zero hints a lie!

Hysteresis is caused in simple phase control dimmer circuits at low settings because in each half cycle the trigger capacitor starts at a different voltage depending on whether the diac fired on the previous half cycle.

A serious issue with this snap-on effect is that if power is turned off at low power setting and re-applied, the controller may not switch on.

Above is type 1, a very triac basic phase control circuit. The red capacitor and resistor to its left are snubber components, the yellow capacitor, 4.7kΩ resistor to its left and the 500k pot are the phase delay circuit, the diac is just visible above the red capacitor. Continue reading A comparo of two bare light dimmer modules

Last update: 10th March, 2020, 9:48 AM

Chinese no-name 1-1000MHz Return Loss Bridge

This article is an expose of the internals of a common Chinese no-name 1-1000MHz Return Loss Bridge available on eBay for around $65 incl post.

Above is the exterior of the device. Specs are sparse: P<23dBm, Directivity>35dB. Continue reading Chinese no-name 1-1000MHz Return Loss Bridge

Last update: 11th January, 2018, 6:00 AM

Where do µ’ and µ” come from?

Lets say we measure the impedance of a 1t wind on a FT240 size core to have Z=13.6+j19.1Ω @ 7.31MHz.

But it has a resistive component, it is not an ideal or lossless inductor.

Nevertheless, we can consider that Z=j*2*pi*f*L, and since Z is complex, a complex values is implied for L. Continue reading Where do µ’ and µ” come from?

Last update: 9th January, 2018, 10:29 AM

Chinese no-name 1-500MHz Return Loss Bridge

This article is an expose of the internals of a common Chinese no-name 1-500MHz Return Loss Bridge available on eBay for around $50 incl post.

Above is the exterior of the device. Specs are sparse: P<23dBm, Directivity>36dB. Continue reading Chinese no-name 1-500MHz Return Loss Bridge

Last update: 11th January, 2018, 6:00 AM

Comparing toroidal inductors of different core dimensions

I often see comparisons of toroidal inductors of different core dimensions with all other characteristics (eg turns, core type, frequency) held the same.

There seems an implicit assumption by many that the bigger the core, the larger the inductance. There are several failure in that thinking.

The ‘inductance’ of a toroidal inductor is µ*n^2*a/l where:

µ is complex permeability, µ0+µr;
n is the number of turns;
a is the cross section area; and
l is the effective magnetic path length.

Note that at RF, permeability may be a complex frequency dependent value, and therefore ‘inductance’ will be a complex value.

Many online calculators incorrectly calculate l from core dimensions using a simplistic formula.

Many online calculators treat permeability as a real number that is not frequency dependent, they use initial permeability (µi). Continue reading Comparing toroidal inductors of different core dimensions

Last update: 7th January, 2018, 11:14 AM

WBT-4000W 230V AC dimmer / motor speed controller

The WBT-4000W is a triac dimmer selling for upwards of $25 on eBay.

It claims:

AC 0V-220V continuously adjustable, zero hysteresis, zero latency, superior heat dissipation.

The question is, does it deliver these things? Continue reading WBT-4000W 230V AC dimmer / motor speed controller

Last update: 22nd December, 2017, 4:18 PM

Review of inexpensive Chinese thermostat – MH1230A

This is a review of an inexpensive MH1230A Chinese bang-bang thermostat that was purchased on eBay for around A$15 complete with thermistor sensor and postage.

Above is the front view of the thermostat. There are many thermostats on the market with similar front panels, but they differ in internals and most importantly, performance and quality.

Above, the rating label is clear and informational, and it does give the sensor parameters. Continue reading Review of inexpensive Chinese thermostat – MH1230A

Last update: 1st March, 2019, 8:24 AM

A flexible test panel for microcontroller based power control projects – #2

This article expands on A flexible test panel for microcontroller based power control projects with some enhancements and accessories.

A LED power meter that I had ordered finally arrived (slow boat from China syndrome).

Above, the upper rail contains a RCD, the power meter which displays Volts, Amps, and kW, or pf, hours, and kWh, a DIN mount terminal block for mains, and a 40A SSR on a heatsink. A clip on CT can be used for oscilloscope observation of mains current. Continue reading A flexible test panel for microcontroller based power control projects – #2

Last update: 15th November, 2017, 6:10 PM