Month: January 2025

Stihl BG85 leaf blower inspection report

This is an inspection report of my 35 year old Stihl BG85 leaf blower.

The blower suffered two faults in its first 18 months:

  • the black fuel hose rotted, unsuitable materials given that the only fuel available here was E10 at that time; and
  • the on/off switch became intermittent sometimes not stopping the engine unless it was operated 10 or more times.

The same two faults occurred in a Stihl line trimmer purchased at the same time, neither were covered by warranty. Since the underlying problem was unsuitable materials and clearly an unreliable batch of switches, and Stihl’s citation of their 12 month warranty terms to escape the cost of repair… I have never bought another Stihl tool, and probably never will.

I baulked at paying Stihl for replacement switches (partly out of concern the new ones might be no better than the failed ones… same source that obviously has a quality control problem), the switches were replaced with compatible ones from China, ~$8 for 10, no faults in the first two selected after 35 years of service.

This thing was run on E10 unleaded from new until about 2009, it was all that was available thanks to Greenies. Stihl oil (bundled with the purchase 50:1 was used until about 2015 when I switched to Amsoil Saber (again 50:1.) Continue reading Stihl BG85 leaf blower inspection report

Last update: 13th January, 2025, 10:12 AM

Why do I keep saying “NOT for Amidon #43?”

Amidon is a reseller, and sells ferrite products.

They sell some products in #43 material. In recent years, they published data for their #43 material, the published characteristics are a copy of National Magnetics Group H material (though they changed the letterhead).

Above is a side by side comparison of the NMG H material datasheet and Amidon 43, the Amidon appears to be a Photoshop treatment of the NMG. Continue reading Why do I keep saying “NOT for Amidon #43?”

Last update: 12th January, 2025, 7:31 PM

A prototype 50:75 RF transformer

The design is of a 50:75Ω autotransformer using a single Fair-rite 5943003801 (FT240-43) core. Note that this data is NOT for an Amidon #43 core.

The winding is a total of 6t tapped at 5t, wound as two close wound layers. The prototype used a single conductor stripped from LAN cable. The winding configuration is an attempt to minimise leakage inductance for improved broadband performance.

This is unconventional, but then the conventional designs on Youtube etc do not usually have credible evidence of low InsertionVSWR or other performance. Continue reading A prototype 50:75 RF transformer

Last update: 12th January, 2025, 7:16 PM

G5RV baluns – a comparison of two options – part 2

This is a follow up article to G5RV baluns – a comparison of two options – part 1 and will make more sense if that article is read first.

Louis Varney, G5RV, described his multiband HF antenna in two forms.

The configuration pictured above using a hybrid of open wire matching section and low impedance coax to the transmitter is very popular.

G5RV baluns – a comparison of two options – part 1 asked the question of whether one of the following two balun options was superior.

Two options from hfkits.com. Continue reading G5RV baluns – a comparison of two options – part 2

Last update: 6th January, 2025, 12:24 AM

NanoVNA-H4 – Surely Smith is better?

A reader of NanoVNA-H4 – VSWR only contended that “surely a Smith chart is superior for antenna system tuning, a universal display.”

Let’s explore that using both VSWR and Smith displays to make tuning adjustments to a real antenna system.

Baseline

Above is a sweep of the antenna system showing both VSWR and Smith chart traces. Continue reading NanoVNA-H4 – Surely Smith is better?

Last update: 5th January, 2025, 8:29 AM

G5RV baluns – a comparison of two options – part 1

Louis Varney, G5RV, described his multiband HF antenna in two forms.

The configuration pictured above using a hybrid of two wire line matching section and low impedance coax to the transmitter is very popular.

Whilst Varney did not recommend a balun, much has been learned about common mode currents in the intervening 70 years, and the use of an effective common mode choke is advisable. A common practice is to locate such a choke at the transition from the two wire line to the coax. Continue reading G5RV baluns – a comparison of two options – part 1

Last update: 5th January, 2025, 8:13 AM

NanoVNA-H4 – charts in Antscope2 and Antscope(1)

NanoVNA-H4 – VSWR only showed how to simplify a NanoVNA to make only VSWR measurements with about the convenience of the traditional hand held scanning analyser.

This article compares measurement of a DUT similar to a common mode choke using NanoVNA and Rigexpert AA-600.

Let’s capture a measurement sweep of a small ferrite cored inductor with a response similar to what you might expect of a good common mode choke for antenna feed lines using a NanoVNA-H4.

NanoVNA-D v1.2.40 firmware

Above is a screenshot of the measurement. The measurement was also saved as a .s1p file to view in other applications. Continue reading NanoVNA-H4 – charts in Antscope2 and Antscope(1)

Last update: 3rd January, 2025, 11:00 AM

NanoVNA-H4 – VSWR only

Hams wanting to resolve an antenna system problem often seek the advice of the assembled experts on social media of one form or another.

They are often advised by many that “you need an NanoVNA”… no matter what they have described, no matter their own capabilities.

Now if they follow that path, it might be the beginning of wonderful things, or it might be a huge frustration.

The problem is that although the NanoVNA is relatively low cost for its capability, affordable to lots of hams, and arguably it can replace whatever they were using previously, but… the requisite knowledge does not come in the box.

There was a generation of “antenna analysers” that were effectively one port VNAs with fixed calibration that provided capability to sweep an antenna system over a frequency range of interest and give a graphical presentation of VSWR, and not a lot of learning required to exploit the thing. (Yes, some of them also provided for a custom SOL calibration).

These type of instruments are still of great utility, though considerably more expensive that the NanoVNA. I have used a Rigexpert AA-600 extensively, but cannot recommend any Rigexpert product, or more generally any current product in this category.

A possible solution

Is there a way to leverage to capability of the NanoVNA to replace the scanning antenna analyser?

This article describes a solution for very common NanoVNA-H4 hardware with SD card, and NanoVNA-D v1.2.40 firmware. The solution may not work for other hardware and firmware.

So, the objective is to simplify the interface to present just a VSWR curve as shown above. Continue reading NanoVNA-H4 – VSWR only

Last update: 3rd January, 2025, 1:56 AM