Designing with binocular ferrite cores – published Al values

Designing with ferrite binocular cores can be frustrating as there are different formats in which data is provided, and data for different mixes on the same dimensioned cores appear inconsistent.

There are several source of the Al parameter for some common cores, often from resellers rather than manufacturers. Continue reading Designing with binocular ferrite cores – published Al values

Designing with binocular ferrite cores – Σ(A/l)

Designing with ferrite binocular cores can be frustrating as there are different formats in which data is provided, and data for different mixes on the same dimensioned cores appear inconsistent.

#61 mix

This article documents calculated geometry Σ(A/l) derived for a number of Fair-rite cores from their specified Al (at µi). Continue reading Designing with binocular ferrite cores – Σ(A/l)

Do Distortionless Lines exist?

I am asked about my use of the term Distortionless Lines from time to time, often in the vein of they don’t exist, so why discuss them?

Concept

The concept derives from the work of Heaviside and others in seeking a solution to distortion in long telegraph lines.

The problem was that digital telegraph pulses were distorted due to different attenuation and propagation time for different components of the square waves.

Heaviside proposed that transmission lines could be modelled as distributed resistance (R), inductance (L), conductance (G) and capacitance (C) elements.

In each incremental length Δx, there is incremental R, L, G and C. Continue reading Do Distortionless Lines exist?

Comparison of BN43-202 / 5t with BN73-202 / 2t for rx only on low HF – small broadband RF transformer – 50:200Ω

Several correspondents refer to my article Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer using medium µ ferrite core for receiving use – 50:200Ω and suggest “I got it wrong, #73 is the proven material choice for such a thing, and a 2t primary is optimal”.

In fact, I did explore #73 as an option, this article presents some key comparisons. The two key statistics shown in this article provided the basis for selecting the design.

Note that the scales are different from plot to plot.

Insertion VSWR

Where the magnetising impedance appears in shunt with an ideal transformer with Zin=50+j0Ω, Insertion VSWR can be calculated.

2t on BN73-202

5t on BN43-202

Continue reading Comparison of BN43-202 / 5t with BN73-202 / 2t for rx only on low HF – small broadband RF transformer – 50:200Ω

Transmission lines: departure from ideal Zo

The article On the concept of that P=Pfwd-Prev discussed the question of the validity of the concept of that P=Pfwd-Prev, exploring an example of a common nominally 50Ω coaxial cable at 100kHz. The relatively low frequency was used to accentuate the departure from ideal.

This article digs a little further with analyses at both 100kHz and 10MHz.

100kHz

A plot was given of the components and sum of terms of the expression for power at a point along the line.

Lets look at the power calculated from voltages and currents for the example at 100kHz where Zo=50.71-j8.35Ω and Zload=5+j50Ω.

Above, the four component terms are plotted along with the sum of the terms. Continue reading Transmission lines: departure from ideal Zo

Basic programming jig for STC15F104E and STC15F204E chips #3

The STC15Fx chips use a simple TTL/CMOS async programming interface that is suited to the common USB-RS232(TTL) adapters. This article describes a low cost programmer that also allows the programming application to Vcc (so initiating the boot loader automatically).

Above is the programmer ($2.50 on eBay) and a small adapter that plugs into the top row of the 2×5 header on the programmer.

DIP-28 are located carefully so that the pins 10-18 are in the socket, the same connections are used for both chip sizes for STC15F104E and STC15F204E. Continue reading Basic programming jig for STC15F104E and STC15F204E chips #3

XH plug savers on the STC U8W & U8 programmer

STC produce the U8W & U8 programmers for a range of their chips.

U8W

The thing has a JST 7way XH socket provided for an ISP connection to a target board. It is accessed through a cutout in the acrylic housing, but the cutout is no bigger than the shoulder on an XH plug and one cannot get tools in beside it to pry the plug out without pulling on the wires.

The good thing is that there is an inexpensive “XH plug saver” sold to the RC market, it provides a means of getting a convenient grip on the plug without pulling on the wires.

First step is to mill out the case opening to accommodate the XH plug saver.

Next, add the XH plug saver to the XH plug, and it all works. Continue reading XH plug savers on the STC U8W & U8 programmer

Garden hose couplers – there has to be a better way

A continuing frustration is garden hose maintenance.

We use reinforced hose that comprises essentially three layers, an inner plastic layer, a braided fibre reinforcing layer and another layer of plastic. Though these layers are bonded in new hose, there is potential for them to separate in service resulting in the reinforcing braid pulling back into the hose length and allowing the hose to expand in diameter at that point (lacking the benefit of the reinforcement). At this point failure of the hose by bursting is inevitable, sooner rather than later.

Some hoses are supplied fitted with factory crimped ferrules, and experience is that they have lasted well except that the fittings are plastic and break if subjected to rough treatment.

User serviceable screw collets fail, either through failure of the collets, or just the outcome of the screw collar loosening and resultant pull-back of the reinforcing braid.

What is needed is a tough and durable coupler with an easily applied ‘permanent’ clamp.

I have conducted a trial of brass fittings modified to remove the screw collar and nylon collet, then used with a stainless steel stepless one ear clamp.

Above at left is the unmodified coupler, and at right the coupler with the collet and screw collar discarded, thread turned off the coupler, and a one ear clamp for installation. Continue reading Garden hose couplers – there has to be a better way

RF transformer design with ferrite cores – saturation calcs

Ferrite cored inductors and transformers saturate at relatively low magnetising force.

#61 material example

Lets work through an example of a FT50-61 core with 10t primary at 3.5MHz.

Magnetic saturation is one limit on power handling capacity of such a transformer, and likely the most significant one for very low loss cores (#61 material losses are very low at 3.5MHz).

Let’s calculate the expected magnetising impedance @ 3.5MHz.

Zm=0.966+j144Ω, |Zm|=144Ω. Continue reading RF transformer design with ferrite cores – saturation calcs

RF transformer design with ferrite cores – initial steps

A review of transformer design

In a process of designing a transformer, we often start with an approximate low frequency equivalent circuit. “Low frequency” is a relative term, it means at frequencies where each winding current phase is uniform, and the effects of distributed capacitance are insignificant.

Above is a commonly used low frequency equivalent of a transformer. Z1 and Z2 represent leakage impedances (ie the effect of magnetic flux leakage) and winding conductor loss. Zm is the magnetising impedance and represents the self inductance of the primary winding and core losses (hysteresis and eddy current losses). Continue reading RF transformer design with ferrite cores – initial steps