Let’s start by reviewing the concept of inductance.
Inductance of a conductor is the property that a change in current in a conductor causes a electro motive force (emf or voltage) to be induced in a conductor.
We can speak of self inductance where the voltage is induced in the same conductor as the changing current, or mutual inductance where the changing current in one conductor induces a voltage in another conductor. Continue reading The private and public scope of coaxial cable
Fox flasher MkII – high power 2 LED solar powered beacon described a LED driver for an animal deterrent using a Chinese 8051 architecture microcontroller, the STC15F104E.
This article documents its failure in June 2019 after five years service. Continue reading Fox flasher MkII – high power 2 LED solar powered beacon – update 6/2019
Fox flasher MkII – high power 2 LED solar powered beacon described a LED driver for an animal deterrent using a Chinese 8051 architecture microcontroller, the STC15F104E.
This article documents its failure in June 2018 after three years service.
With the passage of time, the PV array surface has degraded until solar collection was insufficient to maintain the battery over several heavily overcast Winter days.
Above, a close up of the PV array surface. The pic is of about 8mm width, and one can barely see the silicon stripes which are about 2mm wide. Continue reading Fox flasher MkII – high power 2 LED solar powered beacon – update 6/2018
The ratings for rectifier diode currents are often expressed in terms of a steady (ie DC) current, yet when used as a power rectifier with capacitor input filters, the current is very different.
Above is capture of the rectifier input current for a lab power supply set to 1A load current, the scale factor for the current probe is 1V/A. Continue reading Derating rectifier diode current
The UC3SFL charger for my Hitachi DB3DL2 screwdriver departed this world after just 8 years with a bang, several parts around the main switching transistor deposited as soot inside the cover.
Above is a view of the underside of the charger board, it is very complex, lots of parts, and there are lots of parts on the topside. Ouch, this is going to be expensive.
Yes, it is the replacement power supply is more than half the price of complete tool with two batteries (~$200)… so that is not on.
The screwdriver’s LED control board has already failed (probably a low grade Chinese electrolytic capacitor) and had to be removed as it would switch on spontaneously and flatten the battery. The hole left vacant by the removed push button provides a convenient exit for a charger cable. Continue reading Hitachi DB3DL2 UC3SFL repair
I purchased a further two replacement batteries type NB-6L for a Canon camera from yet another supplier.
Above, the batteries are labelled 1000mAh. They appear to be well made externally, and fit charger and camera fine.
Note that these have different labeling to that shown in the eBay listing. It is naive to expect that the supplied item matches either pics or description, bait and switch is a standard Chinese technique. Continue reading Capacity test of aftermarket NB-6L batteries #2
I purchased two replacement batteries type NB-6L for a Canon camera.
Above, the batteries are labelled 1050mAh. They appear to be well made externally, and fit charger and camera fine.
Note that these have different labeling to that shown in the eBay listing. It is naive to expect that the supplied item matches either pics or description, bait and switch is a standard Chinese technique. Continue reading Capacity test of aftermarket NB-6L batteries
Designing with some common Fair-rite binocular ferrite cores can be frustrating because different parameters are published for different material types, and some are controlled for different parameters.
An approach is to derive the key geometry parameter from the published impedance curves and published material complex permeability curves.
For example, the above curves for a 2843002402 (also common known as a BN43-2402) were digitised and iteratively Calculate ferrite cored inductor (from Al) used for find the value of Al that gives the observed value for Z at 10MHz on the chart above. Continue reading Geometry factors for some common Fair-rite binocular ferrite cores
Finding the resonant frequency of a resonant circuit such as an antenna trap is usually done by coupling a source and power sensor very loosely to the circuit.
Above is Fig 1, a diagram from the Rigexpert AA35Zoom manual showing at the left a link (to be connected the analyser) and the trap (here made with coaxial cable).
Above is the trap measured, the wires were connected as a bootstrap trap as in Fig 1. The coupling link is a 60mm diameter coil of 2mm copper directly mounted on the AA-600 connector, and it is located coaxially with the trap and about 10mm from the end of the trap.
Above is the ReturnLoss plot of the trap very loosely coupled to the AA-600.
Of course this technique will not work on a trap that is substantially enclosed in a shield that prevents magnetic coupling. Note also that many traps used in ham antennas are simply a coil wound on an insulating rod and each end connected to the adjacent tubing, possibly with an overall aluminium tube that may or may not be bonded to the element tube at one end. The latter really become part of the element and measurement separate to the element is not simply translated to in-situ.
The inductor has previously been carefully measured to be 3.4µH. We can calibrate a model of the coupled coils to the observed resonant frequency and ReturnLoss.
Above, the equivalent circuit. We can calculate the flux coupling factor k from the model, it is 2.3% so this is very loosely coupled to avoid pulling the resonant frequency high.
Above is the simulated ReturnLoss response over the same frequency range as measured.
It is practical to measure the resonant frequency of a trap by loosely inductively coupling an antenna analyser, depending on the structure of the trap and the capability of the analyser.
Practical measurements can be explained with a theoretical model of the measurement setup.
Finding the resonant frequency of a resonant circuit such as an antenna trap is usually done by coupling a source and power sensor very loosely to the circuit.
A modern solution is an antenna analyser or one port VNA, it provides both the source and the response measurement from one coax connector.
Above is a diagram from the Rigexpert AA35Zoom manual showing at the left a link (to be connected the analyser) and the trap (here made with coaxial cable.
The advantage of this method is that no wire attachments are needed on the device under test, and that coupling of the test instrument is usually easily optimised.
So, what is happening here? Lets create an equivalent circuit of a similar 1t coil and a solenoid with resonating capacitor.
The two coupled coils can be represented by an equivalent circuit that is derived from the two inductances and their mutual inductance. The circuit above represents a 1µH coil and a 10µH coil that are coupled such that 3% of the flux of 5% of the flux of one coil cuts the other (they are quite loosely coupled, as in the pic above. Continue reading Measuring trap resonant frequency with an antenna analyser