Category: Antennas

This series of articles develops a simple design for a small receive only broadband loop for the frequency range 0.5-10MHz, and to deliver fairly good practical sensitivity.

Fairly good practical sensitivity is to mean that the recovered S/N ratio is not much worse than the off-air S/N ratio. Let’s quantify not much worse as the Signal to Noise Degradation (SND) statistic calculated as \(SND=10 log\frac{N_{int}+N_{ext}}{N_{ext}}\), and lets set a limit that \(SND<3 dB\).

Since Next is part of the criteria, let’s explore it.

External noise

ITU-R P.372 gives us guidance on the expected median noise levels in a range of precincts. Since most hams operate in residential areas, you might at first think the Residential precint is the most appropriate, but ambient noise more like the Rural precinct is commonly observed in residential areas, so let’s choose Rural as a slightly ambitious target.

Above is Fig 39 from ITU-R P.372-14 showing the ambient noise figure for the range of precincts. Readers will not that that are all lines sloping downwards with increasing frequency, so the external noise floor is greater at lower frequencies in this range. Continue reading Small untuned loop for receiving – a design walk through #1

I have written several articles on untuned loops for receiving, as have others. A diversity of opinions abounds over several aspects, but opinions don’t often translate to sound theory.

This article analyses a simple untuned / unmatched loop in the context of a linear receive system.

An example simple loop for discussion

Let’s consider a simple single turn untuned loop with an ideal broadband transformer. The example loop is 3.14m perimeter and 10mm diameter conductor situated in free space. The loop has perimeter 0.0744λ at 7.1MHz, less than λ/10 up to 9MHz, so we can regard that loop current is uniform in magnitude and phase. This simplifies analysis greatly.

Above is a schematic diagram of the example loop. The transformer initially is a 1:1 ideal transformer, it serves to isolate the loop from a coaxial feedline, allowing fairly good loop symmetry and reduction of common mode feed line current contribution to pickup. This works, and subject to symmetry and a good transformer design, it will work well over the stated frequency range, though its gain at some frequencies might not be sufficient to overcome receiver internal noise. Continue reading Small untuned loop for receiving – it’s not rocket science

Small untuned loop for receiving – simple model with transformer gave a simple model for analysing a loop and and Towards understanding the YouLoop-2T at MF/lowHF  applied that to the YouLoop-2T.

Above is the Airspy Youloup-2T. Try to put the two turns thing out of your mind, it is misleading, panders to some common misunderstanding, and so does not help understanding.

It would seem that many are quite confused by information from Airspy. The following quote from an online forum captures the confusion. Continue reading YouLoop-2T and the self resonance bogey at MF/lowHF

Three recent articles developed an explanation of the YouLoop-2T at MF/lowHF:

• Small untuned loop for receiving – simple model with transformer ;
• A transmission line 1:4 impedance transformer ; and
• Towards understanding the YouLoop-2T at MF/lowHF .

The first and third articles explained the concept of signal/noise degradation (SND) statistic, and gave graphs of the behavior of the subject antennas.

This article draws together those SND plots for two antennas, and some variations to the configurations.

Configurations

Simple loop with transformer

Above, the “simple loop” with 0.5:1 ideal transformer. It could be implemented as a shielded loop (with transformer) with similar behavior (but improved common mode suppression). Continue reading SND implications of variations on the untuned small loop at MF/lowHF

Small untuned loop for receiving – simple model with transformer gave a simple model for analysing a loop. If you haven’t already read it, you should. It provides a step towards understanding the YouLoop-2T at frequencies where is is a small loop (perimeter<λ/10).

Above is the Airspy Youloup-2T. Try to put the two turns thing out of your mind, it is misleading, panders to some common misunderstanding, and so does not help understanding.

This is somewhat similar to the simple loop, but now the transformer primary is connected to the loop gap terminals by two parallel sections of 50Ω transmission line, the combination being effectively a 100Ω with similar parameters to the component coax sections. Because of the series connection at the transformer and parallel connection at the loop gap, there is a 1:4 impedance transformation additional to that of the coax sections themselves. Continue reading Towards understanding the YouLoop-2T at MF/lowHF