Evaluating Receive Antennas with a Soundcard

Introduction / Summary
Section (1) . . Receive Antennas
Section (2) . . Signals, and Signal Processing
Section (3) . . Measuring
Section (4) . . Problems and Solutions

This is a webbly-fied version of the presentation given at the RSGB HF Convention in Manchester on November 2nd. 2003. Originally in one piece , it proved a bit too dense for dial-up digestion, so it is now carved up into several smaller parts. It is suggested that they be read in order, since otherwise one might end up with 'Harry Potter Syndrome', i.e. total mystification upon attempting to read the fifth book without the vital base knowledge in the previous four . . .

Clicking on thumbnail images will bring up larger and hopefully more legible versions.

This talk is about antennas, in particular but not exclusively low-band receive antennas and how to measure their directionality. Some work really well, others very disappointingly. But why? Without objective measurement, it's all arm-waving and opinion. But in-situ measurement of fixed antennas has hitherto been practically impossible.
Well, we'll soon fix that.
There are three contributory subjects that need a bit of introduction (in Sections (1) and (2)) before they later intersect. We'll then walk through the measurement technique in Section (3), then in Section (4) a discussion of what can be done to improve the antennas in the light of the results, highlighted by a couple of special case situations.

Section (1) . . Receive Antennas
A brief description of the development and derivation of the popular Terminated Loop ('Ewe-alike') genre of receiving antenna, in particular with details of a loop and an array used as 'targets' for the measuring technique described in Sect. 3.

Section (2) . . Signals, and Signal Processing
An extraordinary and unlikely source of a multitude of predictable test signals. And an introduction to the very powerful software tools that enable their use.

Section (3) . . Measuring
A methodology using the above signals and tools, and some other readily available resources, to plot the azimuth responses of LF and MF receiving antennas with attribution and surprising accuracy.

Section (4) . . Problems and Solutions
Understanding why receive antennas sometimes perform miserably; what can be done about it; using the methods and tools described here to identify, analyse and correct problems.

In summary
This presentation has briefly outlined the development of compact terminated loop antennas, detailed a particular arrangement of a single loop, and more particularly a modestly-sized in-line phased array of loops. These two antennas were used as targets for a novel and reasonably accurate azimuth pattern evaluation technique, which relies upon multitudinous broadcast signals and modern PC-based FFT spectral analysis tools to separate and measure them. The technique allows the plotting of antennas' responses, and the ready examination of environmental effects on their behaviour.

Measuring antenna elevation responses will have to wait for the next episode of 'Mission Impossible'.


Here are a few resources for the "Evaluating Lowband Receive Antennas with a Soundcard" presentation. Please see also the 'Kudos and Links' section.

  • Spectran and Argo from Alberto, I2PHD. Run, don't walk, to get these superb operational tools.
  • DL4YHF's SpecLab Soundcard based FFT audio analysis tool par excellance.
  • FCC's AM Broadcast database. Just fabulous.
  • European Medium Wave Guide. Very comprehensive and useful; a guy maintains this database for fun!
  • Japanese AM stations.

  • © Steve Dove, W3EEE, 2003,4