This article was revised 03/01/2021 to correct an error: the NEC-5.0 model reported was actually the KK5JY LoG, fixed, apologies.
The Loop in Ground project is about a receive only antenna for low HF, but usable from MF to HF. The objective is an antenna of that is small, low profile, and can be located outside the zone where evanescent modes dominate around noise current carrying conductors, like house wiring to minimise noise pickup.
The antenna comprises a square loop of 3m sides of 2mm bare copper wire, buried 20mm in the soil.
This article reports measurement of feed point impedance and a ‘calibrated’ NEC-5.0 model. Continue reading Loop in ground (LiG) for rx only on low HF – #8 measurement and observation
This article explains the technique used at
If we consider a two wire transmission line, we can define currents I1 and I2 flowing in the same direction in each conductor. Continue reading Resolve measurement of I1, I2 and I12 into Ic and Id
There are so many instructional / tutorial videos on the ‘net, and Smith charts are the subject of lots.
But can you trust what you read / see online?
Here an author gives his take on Return Loss.
Errr, no! Continue reading The meaning of the term Return Loss
I purchased a bunch of no-name, no-spec, video baluns on eBay for use with radio antennas at MF and low HF. A pair of these are for transporting 75 ohm coax video signals over twisted pair LAN cable.
Above, the two styles of baluns purchased. Given the label, nondescript as it is, there is quite a possibility that the internals are the same. Continue reading No-name video baluns common mode impedance
This article describes a method of measurement and adjustment using an antenna analyser or VNA to quickly set up a shunt match, a narrow band match (ie for one band, or even only part of the band).
The article uses Rigexpert’s Antscope as the measurement / analysis application, the techniques will work with other good application software.
To demonstrate the technique for matching such an antenna, let’s use NEC-4.2 to create 80m feed point impedance data for a 12m high vertical with 8 buried radials (100mm) and centre loading coil resonating the antenna in the 80m band for simulation of measurement data.
An s1p file was exported from 4NEC2 for import into Antscope, to simulate measurement of an example real antenna.
Analysing the ‘measured’ data
Above is the VSWR curve displayed in Antscope. Note that the actual response is dependent on soil types, antenna length and loading etc, but this is a good example for discussion. It is not real bad, another example might be better or worse. Continue reading Matching a centre loaded 80m vertical – a shunt match tutorial
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
I purchased a Holzforma G372XT chainsaw, it is a Chinese clone of the now discontinued Husqvarna 372XP X-TORQ. It is a relatively new technology carburetted engine without introducing electronic auto tune, a 20 year old design.
There are plenty of online discussions about the 372XP X-TORQ overheating, hot seizures, and pics of blued big ends, scored pistons and bores etc, so whilst the design achieves quite high power output for 71cc, one is warned to pay attention to mixture, fuel quality, and lubrication. This might be an engine that should not be used with other than full synthetic two stroke oil. Continue reading Holzforma / Farmertec G372XT chainsaw – initial evaluation
The article Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – design workup describes a current balun with low Insertion VSWR for operation at modest power levels. The design was based on a low cost Fair-rite 2843009902 binocular core (BN43-7051).
This article documents measurement of the complex common mode impedance Zcm, and calibration of the predictive model.
Zcm is a most useful quantity, it can be used in NEC models of an antenna system. Continue reading Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2843009902 binocular – measurement of Zcm