Loop in ground (LiG) for rx only on low HF – implementation – earthworks

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 that has low Signal to Noise Degradation (SND), and low noise pickup by virtue of some separation of near field radiators.

The antenna comprises a square loop of 3m sides of 2mm bare copper wire, buried 20mm in the soil.

Above is the site marked out for earthworks, but excavation of a narrow slot 25mm deep. On the far side of the loop is an already installed plastic irrigation valve box for the transformer. Continue reading Loop in ground (LiG) for rx only on low HF – implementation – earthworks

Feasibility study – loop in ground for rx only on low HF – signal / noise degradation (SND) – more detail

Feasibility study – loop in ground for rx only on low HF – signal / noise degradation (SND) gave the following graph.

This article explains a little of the detail behind the graph. Continue reading Feasibility study – loop in ground for rx only on low HF – signal / noise degradation (SND) – more detail

Feasibility study – loop in ground for rx only on low HF – signal / noise degradation (SND)

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.

3.5MHz

Let’s take ambient noise as Rural precinct in ITU-P.372-14.

An NEC-4.2 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 Feasibility study – loop in ground for rx only on low HF – signal / noise degradation (SND)

Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer – discussion of ferrite material choice

At 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 I laid out a design using Fair-rite a #43 ferrite smallish binocular core. #43 is a medium permeability NiZn ferrite.

I have been asked by several correspondents why I used #43 when the consensus of online experts is that #75 is a clearly better choice for the application.

Let me say that almost all such articles and posts:

  • are absent any quantitative measurement of their proposed design;
  • they tend to use medium to large toroids; and
  • the few that expose their design calcs treat permeability as a real number that is independent of frequency.

#75 mix is a high permeability MnZn ferrite and subject to dimensional resonance in the frequency range of interest for this application, a problem exacerbated by using larger cores.

Permeability is a complex quantity that is frequency dependent and any analysis that pretends otherwise is not soundly based. Continue reading Feasibility study – loop in ground for rx only on low HF – small broadband RF transformer – discussion of ferrite material choice

Feasibility study – loop in ground for rx only on low HF – SDR for measurement?

A series of recent articles developed a Loop In Ground antenna system design.

To test the prototype, I thought it an interesting exercise to use a low end rx only SDR for the instrumentation, providing a graphic quantitative measure of performance that is within the reach of most hams.

The first device trialled was a RTL-SDR v3 dongle with Sdrsharp (SDR#) software under windows, a very low cost option ($40). I was unable to find meaningful NF specifications or end user measurements for the thing in direct sampling mode. Continue reading Feasibility study – loop in ground for rx only on low HF – SDR for measurement?

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

A simplified design for small broadband RF transformers using medium µ ferrite core for receiving use. The specific application is an impedance transformer for a nominally 200Ω antenna to a 50Ω receiver input. Intended frequency range is from 0.5 to 15MHz.

The characteristic of typical medium µ ferrite mixes, particularly NiZn, are well suited to this application.

This article continues with the design discussed at BN43-2402 balun example, but using a BN43-202 with 5t primary and 10t secondary for a nominal 1:4 50:200Ω transformer (though at high ratios, the transformation is only nominal).

Lets consider a couple of simple starting points for low end and high end rolloff. Continue reading 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

Feasibility study – loop in ground for rx only on low HF – trial topology selection

* * * D R A F T * * * – a working document.

This article documents the selection of the trial loop in ground configuration as a development from the loop on ground antenna (KK5JY).

Baseline

The baseline is a minor variation of a design by KK5JY, a 15′ square loop 20mm above average ground, with 9:1 transformer and 50Ω load middle of one side.

Above is a plot of feed point impedance when the loop is driven. At 3.6MHz, the source impedance for a rx system is 43+j852Ω, and the mismatch loss to a 450Ω load is 11.0dB, a direct contribution to Antenna Factor (AF). Continue reading Feasibility study – loop in ground for rx only on low HF – trial topology selection

Feasibility study – loop in ground for rx only on low HF

* * * D R A F T * * * – a working document.

This article documents a feasibility study of a smallish loop on or in ground as a rx only antenna for 160-40m, possibly with advantage in high noise environments.

Various ‘on ground’ antennas are discussed online etc, but there is a distinct lack of supporting scientific evidence though subjective anecdotal evidence abounds.

The approach used here is to determine the degradation of S/N resulting from a low gain antenna system in the context of expected ambient noise as per ITU P.372-13. The analysis leans to the conservative side. Continue reading Feasibility study – loop in ground for rx only on low HF