Fair-rite’s ‘new’ #61 permeability data (2021)

Fair-rite publishes spreadsheets of the complex permeability characteristic of many of the ferrite mixes. This note is about #61 mix.

I have published various tools and articles based on the undated pre 2021 published data, and measurement results reconciled quite well with that data, taking into account the tolerance on the products.

I have added the #61 data I downloaded recently (unfortunately the files do  not contain a date), and included the data in Ferrite permeability interpolations as shown in the above screen shot.

Above is a comparison of the two datasheet csv files.

Last update: 31st December, 2024, 6:25 PM

NanoVNA-H4 – inductor challenge – part 9

This article continues on from NanoVNA-H4 – inductor challenge – part 8, this time with an inductor that might be a candidate for a plate RF choke for a HF valve PA.

Above is the prototype DUT, it is 142t of 0.25mm enamelled copper wire close wound on an 18mm PMMA (acrylic) former, it measures 130µH well below first self resonance.

Let’s sweep it with a NanoVNA. Continue reading NanoVNA-H4 – inductor challenge – part 9

Last update: 30th December, 2024, 5:53 AM

Perplexity AI calculating Zo of a two wire transmission line – comparison with measurement – updated

During the process of writing the article Analysis of output matching of a certain 25W 144MHz PA an estimate was made of the characteristic impedance Zo of a section of twisted enamelled 0.71mm copper wires.

Perplexity AI

Let’s ask Perplexity AI for an answer.

Perplexity AI gives approximately 108Ω. Continue reading Perplexity AI calculating Zo of a two wire transmission line – comparison with measurement – updated

Last update: 1st January, 2025, 7:15 PM

Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting – a recovery

This article documents measurement of a prototype two element Yagi for Fox Hunting / portable direction finding: Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting . See the original article for the design criteria.

Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting – measurement showed a prototype and measurements.

Above, the antenna with MySondy custom firmware for a TTGO.

In Bruce’s own words…

Continue reading Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting – a recovery

Last update: 17th December, 2024, 10:04 PM

Is it possible to predict the terminal voltage of an installed antenna with feed line – #2?

Is it possible to predict the terminal voltage of an installed antenna with feed line? discussed prediction of an intended antenna using an NEC model.

ATU terminal voltage

This article shows how to predict ATU terminal voltage based on VNA or analyser measurement of the antenna system looking into the feed line. We will also look at an example of the voltages within a T ATU.

Above is a calculation of peak voltage at the ATU antenna terminals at 100W calculated from a saved .s1p file made looking into the feed line from the ATU position.

Above 3MHz, these voltages are modest at 100W. These voltages are impressed upon the balun that sits between feed line and ATU via 300mm of RG-400. Realise that at 1600W, the voltages would be four times that in the graph, ie up to about 3000V at some frequencies. Continue reading Is it possible to predict the terminal voltage of an installed antenna with feed line – #2?

Last update: 14th December, 2024, 11:58 AM

Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting – measurement

This article documents measurement of a prototype two element Yagi for Fox Hunting / portable direction finding: Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting . See the original article for the design criteria.

A prototype was constructed and tuned to approximately mid band.

Above, the antenna with MySondy custom firmware for a TTGO. Continue reading Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting – measurement

Last update: 13th December, 2024, 3:44 PM

Prototype 2el Yagi for 146MHz Fox Hunting – measurement

This article describes VK4MQ’s (Bruce) build of the antenna and documents measurement of the prototype two element Yagi for Fox Hunting / portable direction finding: Prototype 2el Yagi for 146MHz Fox Hunting . See the original article for the design criteria.

A prototype was constructed and tuned to approximately mid band.

Above, the antenna pointing at the zenith for measurement. Continue reading Prototype 2el Yagi for 146MHz Fox Hunting – measurement

Last update: 12th December, 2024, 12:12 AM

Toro MX4250 rear tyre mid life maintenance

The Toro MX4250 is a ZT ride on mower (riding mower).

A recent inspection at 220h revealed that rear tyre wear is uneven (as would be expected for this type of application), tread depth inside to outside was 1.5/2.5mm and 1.8/2.6mm.

To wring a little more life out of the tyres, they were reversed on the rims, and rotated left to right.

Small diameter wheels, especially wide ones can be difficult (these are 18×7.50-8 tyres), but these were much easier than the front castors which needed tubes inserted when the mower was quite new.

Above, a Bead Cheata was used to break the bead. On one side of the wheel, the bead needs to be forced down more than 50mm, the other side is easier. Beyond that, tyre levers were sufficient. I used a little mounting lube on the beads to remount the tyres, that makes the job a lot easier. The tubeless tyres reseated for inflation pretty easily, a few bounces of the wheel and they inflated just fine. Continue reading Toro MX4250 rear tyre mid life maintenance

Last update: 11th December, 2024, 8:49 AM

“CM choke acts like the cut-off end of a wire antenna?”

A poster on social media recently wrote:

Remember that a CM choke acts like the cut-off end of a wire antenna. That includes performing the reflection that creates the  standing wave for resonance – it IS your ‘end point’ for the frequency  it’s built for and any higher frequency.

Let’s explore that proposition with two simple NEC models.

A half wave dipole above average ground

The baseline model is a half wave dipole 10m above ‘average’ ground (σ=0.005, εr=13).

 

Above is a graphic of the current distribution on the wire. The current distribution is the classic half wave dipole current distribution, approximately sinusoidal in shape and falling to approximately zero at each end. Continue reading “CM choke acts like the cut-off end of a wire antenna?”

Last update: 7th December, 2024, 3:54 PM

Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting

This article documents a design prototype for a two element Yagi for Fox Hunting / portable direction finding of Radiosondes on 401MHz.

Design criteria:

  • compact;
  • good symmetry;
  • good front/back ratio;
  • deep nulls at the side;
  • easy DIY construction; and
  • low cost.

The design is for a two element Yagi using a Half Folded Half Wave Dipole driven element and reflector. The driven element was covered by US Patent 6307524 which may have expired.

A model was constructed in NEC-4.2 and adjusted to meet the design criteria.

Above is a diagram of the Yagi elements. The driven element feed arrangement has an integral balun and 1:4 impedance step up ratio allowing a close spaced configuration matched to 50Ω coaxial feed line. Continue reading Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting

Last update: 2nd December, 2024, 5:33 AM