Search Results for: Choke

The obsession with measuring extreme spot frequency impedances of broadband common mode chokes

The fashion for measuring HF broadband common mode chokes for antenna systems is to use the s21 series through measurement technique, the basis for which is specious as discussed elsewhere on this blog. Let’s look at an example common mode choke, this time for suppression of ham transmitter ingress to a VDSL2 line. The spectrum … Continue reading The obsession with measuring extreme spot frequency impedances of broadband common mode chokes

VNA fixture for measuring Zcm of a common mode choke – twisted pair wound

VNA fixture for measuring Zcm of a common mode choke – coax wound discussed issues with common ham practice for measuring coax wound common mode chokes. The article left readers with some homework: Does the same thing occur if the core is wound with twisted pair that is well represented as a uniform two wire … Continue reading VNA fixture for measuring Zcm of a common mode choke – twisted pair wound

VNA fixture for measuring Zcm of a common mode choke – coax wound

A common online question is what sort of fixture is appropriate to measure the common mode impedance of a common mode choke. Above is a screenshot from a Youtube video by Trx Lab, probably about 2016 vintage. I see many problems with the fixture, lets start with the resistors. Last update: 3rd January, 2024, 11:17 … Continue reading VNA fixture for measuring Zcm of a common mode choke – coax wound

Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues

At Ferrite cored RF chokes in Class-E RF power amplifiers a design was offered for a choke using a Fair-rite 2843000202 core (commonly sold as a BN43-202), and the point was made that some products sold as BN43-202 might be significantly different. Let’s look at the calibrated model estimates of choke impedance and core loss, … Continue reading Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues

Ferrite cored RF chokes in Class-E RF power amplifiers

Class-E RF power amplifiers have become quite fashionable in ham radio in the last decade or two. This article discusses a common issue with the design of the RF choke providing DC to the Class-E stage. Above is a circuit above is from (Sokal 2001) which explains the amplifier and gives guidance on selection of … Continue reading Ferrite cored RF chokes in Class-E RF power amplifiers

nanoVNA – measure common mode choke – it is not all that hard!

It seems that lots of hams find measuring the impedance of a common mode choke a challenge… perhaps a result of online expert’s guidance? The example for explanation is a common and inexpensive 5943003801 (FT240-43) ferrite core. Expectation It helps to understand what we expect to measure. See A method for estimating the impedance of … Continue reading nanoVNA – measure common mode choke – it is not all that hard!

Optimal common mode impedance of a common mode choke

In recent days we see two online experts with diametrically opposite views of the optimal common mode impedance Zcm of a common mode choke… …the inductance of the CMC is responsible for the CM attenuation. and… A practical choke is RESISTIVE, not INDUCTIVE. Emphatic statements indeed. They are very unlikely to both be correct, and … Continue reading Optimal common mode impedance of a common mode choke

An example and explanation of unexpected common mode choke flashover

An online discussion is developing the design of an ultimate common mode choke, at it reached a stage considered final when a transmit test revealed it could not withstand the unstated transmitter power. The designer did report measurement at the choke looking into the feed line giving Z=493-j740Ω @ 3.8MHz. There are questions about the … Continue reading An example and explanation of unexpected common mode choke flashover

what-exactly-happens-to-the-signals-hitting-a-common-mode-choke?

An image from what-exactly-happens-to-the-signals-hitting-a-common-mode-choke doesn’t quite look right. In respect of the first part, inductance so if the windings are equal, half the total current flows in each winding and each contributes flux due to i/2, total current is i, total flux is twice that due to i/2, so the inductance of the parallel equal … Continue reading what-exactly-happens-to-the-signals-hitting-a-common-mode-choke?

Some pretty woolly thinking about the operation of common mode chokes in antenna systems

One of the notions one often sees discussed is that at RF, some device inserted in a relatively long (meaning wrt wavelength) conducting path is likely to lead to interruption of the circuit in the way that a switch might in a DC circuit. Another variant is one where current flows on one side of … Continue reading Some pretty woolly thinking about the operation of common mode chokes in antenna systems