Refurbishing the push button in action cam cases

In my experience, action cam underwater / weatherproof transparent cases have buttons that are quite difficult to use. This seems mostly because they are assembled with no lubricant.

Above, the button in the genuine Sjcam SJ8  has a stainless spring, shaped washer, two 6x2x2mm orings, and a 2.5mm E clip. This pic shows that the thing is assembled dry which makes operating pressure high, and in any event not smooth as the button shaft is not particularly smooth. Continue reading Refurbishing the push button in action cam cases

Last update: 30th August, 2019, 6:49 PM

Matching a 5/8λ ground plane – a single stub tuner example

A chap seeking details for a matching inductor for his 5/8λ vertical on 20m reported “my AA54 RigExpert analyser gives the following reading (SWR 8,2). (R 81,5). (X -158) ” measured looking into a “length of rg58 about 15-20 cm” and asked “is the inductor coil going to be enough or will I need an L match to bring the real resistance to 50 ohms”. Continue reading Matching a 5/8λ ground plane – a single stub tuner example

Last update: 3rd September, 2019, 7:07 AM

Trapped dipole

Some time ago I wrote some articles on so-called Coax Traps, and an example design of an Inverted V dipole for 80 and 40m.

A coax trap (before cross connection).

The whole subject of trapped antennas elicits a lot of online discussion that is often more about semantics than understanding. Continue reading Trapped dipole

Last update: 28th August, 2019, 12:11 PM

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

Last update: 26th August, 2019, 7:07 AM

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)

Last update: 27th August, 2019, 7:26 AM

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?

Last update: 21st August, 2019, 9:00 AM

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

Last update: 23rd August, 2019, 1:32 PM

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

Last update: 19th August, 2019, 11:47 AM

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

Last update: 18th August, 2019, 7:57 PM

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

Last update: 16th August, 2019, 7:49 PM