LOOP ON THE GROUND.

Uncategorised / 24 January 2021 / Leave a Comment

THE SOLUTION FOR OUR NOISE LEVELS?

By ZS1XB Emil Böhme

With the collaboration of ZS1ML Marius Lubbe

The ground loop antenna; also known as LOG ( L oop; O n the; G round) is a concept that sounds impossible but works great.

Following our high noise levels over the last few years, I started looking at devices and antennas that take up less noise.

Several electronic devices have disappointed me and I have started researching antennas.

ZS1ML Marius Lubbe sent me a shortcut to a YouTube video in which Scott, WX0V discusses the antenna of Matt Roberts KK5JY and gives a good description of his use of a ground loop Rx receiving antenna that absorbs much less noise. & nbsp ; https://www.youtube.com/watch?v=wMb8i5QajW0

As we all know, this is not a new concept and the old famous Beveridge antenna by Harold Beveridge (1921) is one example of this.

The aim is to obtain specific noise level characteristics especially during competitions, DX Expeditions and simply local HF band noise.

As in the picture below, such an antenna will be installed flat on the ground to receive HF airwave signals from different angles but very low. The loop antenna can apparently also be mounted just below the ground surface but I did not try it myself.

Marius did put one about 5cm under the ground and told; he is amazed at how well it works to bridge noise levels. This is not due to weaker signals, on the contrary the signal is strong, but the noise is at least about 3 to 4 S points lower than normal, on a typical day. Where previously you only heard noise, suddenly clear voices emerge from the signal when you turn on the LOG. This is really remarkable.

Photo 1

Description of the antenna

The basic concept is a square loop that is mounted on the ground. The perimeter may vary. A larger loop will of course work better for the lower 40m and 80m bands.

I went on to choose a 20m loop with each leg of 5m and set reasonably square. See Photo 1 .

The best receive signals will be from the direction of the arrows., depending on the feedpoint. Fig 2.

The loop can then be fed as everyone would like to arrange in their yard or space. From FIG. 3 can be seen the feeding point can even take place in the middle of a leg.

I placed my loop in my car driveway in front of the garage by inserting a few screws into the grooves between the stones as seen in Photo 1.

Marius planted his in the wife\’s garden, right under her nose, and no one is the wiser…

The Transformer

To get the signals, as a next step you have to build a transformer that reconnects the loop and the feed line.

I used a 7 meter long RG58 coax for the experiment. Marius used cheap 70-ohm TV antenna wire, with the same results.

Building the transformer / adapter requires some components as listed:

• Square plastic case – does not need to be large
• SO239 connector
• Two stainless steel or copper screws with washers and bolts.
• Two ring connector as shown in Photo 1 .
• One “binocular ferrite” BN-73-2020 See Photos 2 and 2a.

 Photo 2                                                                                                                 Photo 2a

I tried various versions and even glued two T50 toroids together with Super Glue.

Photo 3

The next step is to build the transformer / adaptation section. First, the ferrule must be fed with a ratio of two turns for the coaxial side and 5 turns for the loop antenna portion. See Fig. 1

Fig 1.

                 One turn on the ferrule.

                                                                Two turns on the ferrule.

See the finished prduct pe-installation Photo 4 above. the fully completed transformer can be seen in Photo 5 below.

Receiving antenna test :

The antenna lends itself very well to a better, much lower, noise level reception.

During the experiment, I especially compared the 40m, 30m 20 and 17m tires. Marius reports that with a similar loop antenna he has especially good results on the 80m band.

What was striking was that with my vertical or even EFHW antenna I sometimes could not follow a conversation on HF and the signal was very low and inaudible. So I put my TX antenna on an antenna switch with the ground loop antenna as the second option.

To my surprise I was able to receive and make out much clearer signals especially on SSB.

The noise levels here in Paarl, Cape Town, where I live, sometimes run from S7 to S9 plus.

When I then switch to the ground loop antenna, the noise will typically drop to a level S1 to S3.

The only disadvantage with some radios is that when you want to call a station, the operator has to physically switch to the TX antenna.

Marius has a Kenwood T\’S-590 and it comes with an Rx antenna socket at the back, which then makes the operation easier, because you listen to the Rx antenna and when you press the PTT it automatically switches on the other selected antenna to carry the signal.

I played with the antenna for several weeks and was amazed that the noise level was constantly so much less for the loop antenna on the ground.

Photo 5

So, in the end, everyone should consider building such a cheap ground loop antenna for experimentation to experience the difference first hand. It\’s value for money now!

Marius and I strongly recommend that the contest people in particular take this solution to the current high noise levels seriously and try it out where you are located, we would love to hear your feedback..

We wish you many contacts and pure reception.