Many thanks Adrian for the document. Good job indeed.

73's Pino I2BGQ

There does seem to be some confusion regarding both the directivity and polar response of this antenna. In order to clarify things please see the attached PDF which I hope will clear up any confusion. My apologies if this is already well-known to you.

Adrian, 5B4AIY

Hi Adrian,

your test shows a fantastic result, I think you did a very good job. I do agree with you on the possible cause of the different behavior of the antenna on various frequencies, and that is what I experienced when looking at my signals on the waterfall of the SDR receiving stations on line in the world. Sometime contradictory, but a doubt rised in me also reading an article of an OM in the web, speaking of the same phenomenon.

Anyway, thanks a lot for the explanation, it clarified all my doubts, and encuraged me to experiment with this interesting antenna again. I have esperience with many types of antennas, especially with a 3 elements SteppIR which I have used for many years. But now that I've moved house I have to deal with the limited space available, and I don't have access to the roof of this house, So this Baby Loop is the antenna that is ideal for my use.

73's, Pino I2BGQ

Hi, Pino,

I was intrigued by your findings so I decided to conduct a directionality test of my own with the help of my friend John, 5B4AMR. He is about 15km away from me and he used his transceiver in the FM mode to give a continuous carrier whilst I measured the received signal strength with my Siglent spectrum analyser. I am attaching a PDF file showing the test results. Generally speaking, it tends to confirm that the forward direction of the antenna is indeed in the direction of the gamma match as shown in the picture I sent you. This was taken from an article I wrote reviewing the Ciro-Mazzoni 'Baby' loop which was published in the RSGB magazine RadCom in December 2019.

Bear in mind that this test was hardly conducted using a proper antenna test range, and the results are only approximate. The first thing to notice is the almost complete absence of the deep null at right angles. This suggests that I was receiving both sky wave and ground wave propagation, and for the sky wave component the antenna is virtually omni-directional. This was confirmed by the 40m and 30m results where I could see the signal strength slowly varying as the skywave component came in and out of phase with the ground wave. Using a local signal source located in the antenna's far field but much closer showed a deep null of about 17dB at right angles. This signal source also confirmed that the main lobe is in the direction of the gamma match with the forward direction being about +3dB compared the reverse direction.

The contradictory 20m result where the signal strength was greater off the 'back' of the loop can be explained by the fact that the skywave component was probably stronger than the ground wave and partially out of phase, and as a result with the lower ground wave level off the back of the loop the resultant signal strength was greater.

I intend to repeat this test but locating a transceiver much closer but still in the far-field and so that the ground wave signal would be sufficiently strong as to essentially swamp any skywave component. Stay tuned!

73, Adrian, 5B4AIY

Hi, because the loop uses a modified gamma match there is a 6dB difference in the gain or radiation pattern of the antenna between forward and reverse directions. The forward, or main direction, is in the direction of the gamma match. In other words, where the gamma match is connected to the loop is the forward direction. See attached annotated image.

However, this is only true for low radiation angles, much less than 30 degrees. Above about 30 degrees the antenna becomes essentially omnidirectional.

If you need any further information, let me know.

73, Adrian, 5B4AIY