Reassembling a certain common chainsaw clutch

I managed to drop a chainsaw clutch and it separated into its component parts.

Thinking there would be a simple trick to this, I consulted Youtube. It turns out that reassembling these has proved a challenge for many people, and their online posts informed as to what approaches don’t work well, describing the many hours spent trying to reassemble. One online expert advised buy another, they are so cheap.

Above is a clutch of the type I will discuss, mine is from a 45-58cc Chinese chainsaw. There are variants, and the technique may be adaptable to them. Continue reading Reassembling a certain common chainsaw clutch

Last update: 11th June, 2021, 5:13 PM

Another small efficient matching transformer for an EFHW – 2643251002

This article describes a small matching transformer built and measured by Luis, CT2FZI, using a Fair-rite 2643251002.

Above is the transformer with 100pF compensation capacitor across the input, and two resistors to make up a 3300Ω load in combination with the VNA port. Continue reading Another small efficient matching transformer for an EFHW – 2643251002

Last update: 14th April, 2024, 1:35 PM

Shorting winding sections of a ferrite cored EFHW transformer

A chap recently posted some advice on construction of a dual ratio transformer for EFFHW antennas, advice with an informative pic, but without measurement evidence that it works well.

Pictured is a dual UnUn. I made this for experimenting. It’s both a 49 and 64 to 1 UnUn.

The 49 to 1 tap uses the SS eye bolt for the feed through electrical connection and the SS machine screw on the top is the 64 to 1 connection. If I want to use the 49 to 1 ratio, there’s a jumper on the eye bolt that connects to the top machine screw where the antenna wire is attached. The jumper shorts out the last two turns of the UnUn. Disconnect the jumper from the top connection and now you have a 64 to 1 ratio.

Continue reading Shorting winding sections of a ferrite cored EFHW transformer

Last update: 14th April, 2024, 1:35 PM

RF Power Meter 2 (RFPM2) – display update

RF Power Meter 2 is a logging RF power meter based on AD8307 and ESP8266.

The original LCD display was white on blue, but was very difficult to read at some viewing angles, so it had to go. Unfortunately I could not find more displays with that hole pattern, it seems to have been discarded for a newer hole pattern as almost everything I looked at had the same newer patter.

So, the box front needed rework, and there would be visible spare holes… so a dress escutcheon was designed in Freecad and cut on a CNC router.

The escutcheon was designed to be cut from some 3mm black acrylic sheet that was on hand, and it would cover the reworked panel. Continue reading RF Power Meter 2 (RFPM2) – display update

Last update: 12th June, 2021, 7:43 AM

Small efficient matching transformer for an EFHW – a Simsmith model

This article offers a simple Simsmith model for the Small efficient matching transformer for an EFHW.

Above is the model topology. D1 is a daemon block which essentially, calculates key values for the other blocks based on exposed parameters and the named ferrite material complex permeability data file. The prototype used a Fair-rite 2643625002 (#43) core. Continue reading Small efficient matching transformer for an EFHW – a Simsmith model

Last update: 14th April, 2024, 1:35 PM

A simple generic Simsmith model of a linear push-pull Class B broadband HF power amplifier

This article outlines a Simsmith model developed to explore / confirm behavior of some linear Class B push-pull HF broadband power amplifiers.

The design is for a system power output of about 80W on a 24V supply, it is a combination that should work with practical system components with good efficiency.

Above is a first step, an estimate of an initial load line for the PA. The calculator is written in valve terms, but is quite applicable to this scenario. Continue reading A simple generic Simsmith model of a linear push-pull Class B broadband HF power amplifier

Last update: 11th June, 2021, 7:42 AM

Ferrite cored inductors at HF – flux, loss and saturation

I see online experts opine that small signal characteristics (eg complex permeability curves) of ferrite toroids are not valid for applications such as RF common mode choke in transmitting antennas.

Others opine that saturation is a practical design limit, and for example that Bs/2 is a safe / appropriate design target.

Let us consider a ferrite cored inductor at 7MHz. The inductor comprises 11t on a 11t on Fair-rite 5943003801 (FT240-43) toroid. This is a medium to high permeability ferrite material, and for that reason, has significant loss at HF. Higher and lower permeability materials are fashionable at different times, the higher permeability #31 mix is fashionable at this time.

I will work in MKS units.

Above is Fair-rite’s B-H curves for #43 material. Let’s take saturation flux density Bs to be 1500gauss or 0.15T. Continue reading Ferrite cored inductors at HF – flux, loss and saturation

Last update: 16th January, 2024, 7:44 PM

SNTP synchronised clock v1 – boxing it up

The SNTP synchronised clock (ssc) is an ESP8266 based time of day clock with an LED display.

The code is fairly mature, and the boxed prototype will be build with a large 4 digit 7 segment LED display (1.2″ or 30mm) using the HT16K33 driver chip.

The prototype will be housed in an ABS Jiffy box, and a new lid cut from dark red transparent acrylic on the CNC router.

Above is the sketch of the layout. The screw holes in the display are M1.6, and there is no clearance for larger screws. Continue reading SNTP synchronised clock v1 – boxing it up

Last update: 13th June, 2022, 2:26 PM

EB104 alternative output circuit

One of the very important designs of HF broadband MOSFET power amplifiers was that of Helge Granberg in Motorola application note EB104.

This article offers an explanation of how the the alternative output circuit at Fig 5 of EB104 works.

Let’s look at the schematic diagram of the PA.

Above is the schematic from EB104, of interest for this article is the output circuit comprising T2 and T3 which are intended ideally to provide a drain to drain load of 50/9=5.55Ω. Continue reading EB104 alternative output circuit

Last update: 25th May, 2021, 10:05 AM

A desk review of the MiniPa100 kit – #2: transformer T2 turns ratio

This article is on in a series of a desk review, a pre-purchase study if you like, of the MiniPa100 kit widely sold on eBay and elsewhere online.

Previously…

The above pic from an eBay advertisement of the 2020 version of the PA would suggest very strongly that there are three turns on the secondary of the output transformer, and a half turn on each drain. Interestingly the 70W versions also appear to use three turns, alarm bells ring!

Here is a little table that shows the maximum power obtainable with a transformer of this type for various supply voltages and secondary turns. Continue reading A desk review of the MiniPa100 kit – #2: transformer T2 turns ratio

Last update: 11th June, 2021, 7:42 AM