The article Another small efficient matching transformer for an EFHW – 2643251002 – #1 – design workup lays out the first steps in a design. This article documents bench measurements of a prototype transformer.
Above is the prototype transformer wound with 14t of 0.71mm ECW tapped at 2t. The mm rule gives some scale. The turns are close wound, touching on the inner diameter of the core. Continue reading Another small efficient matching transformer for an EFHW – 2643251002 – #2 – prototype bench measurement
The article Another small efficient matching transformer for an EFHW – 2643251002 described a correspondent’s , Luis, CT2FZI, implementation of the transformer.
I have also had lengthy discussions with Faraaz, VK4JJ, who is experimenting with a similar transformer.
This article describes my own design workup and measurements using a Fair-rite suppression core, 2643251002. The cores are not readily available locally, so I bought a bunch from Digi-key.
I really resist the tendency in ham radio to design around unobtainium, it is often quite misguided and always inconvenient. In this case, the motivation for these cores that use quite ordinary #43 material is the geometry of the core, they have ΣA/l=0.002995, a quite high and rivalling the better of binocular cores. High ΣA/l helps to minimise the number of turns which assists broadband performance. See Choosing a toroidal magnetic core – ID and OD for more discussion.
- InsertionVSWR<2 3-22+MHz;
- nominal 49:1 transformation;
- autotransformer; and
- 50W average power handing.
Some key points often overlooked in published designs of EFHW transformers:
- Insufficient turns drives high core loss; and
- leakage inductance is the enemy of broadband performance, so the design tries to minimise leakage inductance.
Note that high number of turns drives high leakage inductance, so the design is to a large extent, a compromise between acceptable core loss and bandwidth.
Initial design estimate
From models, I expect that a turns ratio of 2:14 (ie 14t tapped at 2t) is likely to deliver the design criteria (with suitable compensation capacitor).
Above is a perhaps ambitious initial objective using a simple model of the transformer, dotted line is Loss and solid line is InsertionVSWR. Continue reading Another small efficient matching transformer for an EFHW – 2643251002 – #1 – design workup
Feasibility study – loop in ground for rx only on low HF laid out an initial design concept. This article sets out expected signal / noise degradation in a typical installation.
Let’s take ambient noise as Rural precinct in ITU-P.372-14.
An NEC-5.0 model of the 3m a side LiG gives average gain -37.18dBi. An allowance of 2.7dB of feed loss covers actual feed line loss and mismatch loss. Continue reading Loop in ground (LiG) – #6 signal to noise degradation (SND)
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
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
On review of the Ultrafire XML-T6 torch, I found the mode switching / mode memory so dysfunctional that it rendered the torch useless in my evaluation.
At Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’ I gave a fix for that revision of the electronics, and updated it with description of a later fixed production model.
Years later, I bought two more of these due to switch failures on the originals… and guess what, the flash on power on returns.
Let’s pull them apart.
They have a new revision / version of the LED driver PCB, and it has provision for a resistor in parallel with the capacitor, but the resistor pads are not populated.
Above, the LED driver board with a 100k resistor added, it is the far component. This was an 0805 part that was on hand, but ideally should be a 0603. Continue reading Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’ #2
The MXITA SMA-8 is a low cost torque wrench for 8mm, specifically for SMA connectors. It has an adjustable calibration, supplied at 1Nm but easily adjusted down to 0.6Nm to suit common brass SMA connectors, especially of doubtful quality.
I bought this after seeing several recommendations on a nanoVNA forum.
Above is the factory pic of the SMA-8. Continue reading Review of MXITA SMA-8 #2