Martin builds a simple ferrite rod to inductively couple radios to his external mediumwave antenna

21 Replies

Many thanks to SWLing Post contributor, Martin Tobisch, who shares the following guest post and videos from his home in Malta:

New AM Signal Coupler

Many AM medium wave listeners are looking for solutions to improve the reception performance of their radios.

After many attempts, which I don’t want to entertain anyone with, a coupler was created that feeds the external antenna directly into the ferrite antenna. I use my 66 foot long wire antenna on 50 ohm RG-58 cable, but other antennas will have similar success.

The clips available on YouTube speak for themselves:

 

Experiments with smaller ferrites and antenna rods met with no success. It is important that the coupler still works even at a distance from the ferrite antenna and without precise alignment.

With tube radios it easily bridges the distance from the housing to the ferrite rod Antenna
The finished coupler consists of 6 NiZn ferrite cores, which are connected with glue to form a rod. 8 turns of wire are wound over this and soldered to an RG-58 cable. Some electrical isolation tape and ready. So far I’ve just put it in a box. Of course there are finer solutions and it should be protected against shock. Ferrite cores are notoriously brittle.

Here is a link to the ferrites used (purchased at AliExpress).

Advantages: Advantages to what? Nothing comparable exists.

So there are advantages to feeding via an antenna socket. The signal coupler is also good for radios without an antenna socket. But in case of using an antenna socket, common mode wave interference picked up in the house goes unlimited into the radio. Due to the magnetic coupling to the ferrite antenna, common mode waves are completely suppressed. They do not create a magnetic field in the coupler.

No changes are necessary in the radio

The biggest advantage is, that you can listen to distant stations loud and clear, which previously only produced a quiet scratching noise.

I very much welcome reports of experiences.

[email protected]

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21 thoughts on “Martin builds a simple ferrite rod to inductively couple radios to his external mediumwave antenna”

    1. Martin Tobisch

      Hello Adam

      Thank you for your Mail. In my case i use my 66 Ft EFHW Antenna. There is a 49 to 1 Unun between. But you know the 66 Ft antenna is not made for Medim Wave but it works perfect. In your case a 10 Meter wire with nothing extra on the roof, I would say try it. A 9 to 1 unun could make it better, but these things need to be tested. And please let me and the others know your results. Its a real interesting Topic
      Have fun with your radio an 73s

      Reply ↓
  4. Julio Cesar Pereira

    Very good! I have an LW/MW ferrite rod antenna with a tuning capacitor I use with my radios. It was manufactured by the DX Club of Brazil. It is incredible how it enhances any radio that has a bult-in ferrite antenna. I use it with a Sony ICF-2010, one of the most sensitive radios on MW. A station a signal that does not light any led from the S-meter suddenly lights up half of the LEDs. I have the 2001 laying on a stand that is on a revolving plate.

    Reply ↓
  6. Bill Alpert

    A few years back I created something similar using a large amount of wire winding around 2 end to end imported ferrite rods from the Ukraine all mounted in/on a piece of PVC pipe. I used a small butterfly capacitor to make it tunable. There was a lot trial and error with the winding and my first attempt ended up being resonant in the shortwave bands just above medium wave. The resulting device is quite a bit larger than your design, and is very directional, so orientation is key.
    I’d love to see the building details of your project, if available.
    73 de Bill Alpert/ KG6NRV

    Reply ↓
  7. Bill Hemphill

    Hi Martin,

    Very interesting on using ferrite cores glued together. I’ve seen some similar using ferrite rods put together.

    I do something similar. I have a regular AM ferrite rod antenna out of an old am radio. It’s placed in a plastic box. I can then hook an antenna to it and place the box next to the radio. Like you found, it does work wonderful.

    I also have a 27″ tunable hula-hoop style am loop antenna. Normally, I would just place the radio inside the loop and then rotate and tune the loop for best reception.

    But if the radio has an antenna input that disables the ferrite antenna in the radio, I can place the box inside the loop and then cable from the box to the radio. This gives the best results.

    73
    Bill WD9EQD
    Smithville, NJ

    Reply ↓
  8. Bert Schuur

    When I was about 12 years old I found out that if I connected a long wire to the cv radiator (earth) and looped it a few times around my transistor radio, mediumwave reception sensitivity increased dramatically. Increasing or decreasing the number of loops acted as the antenna attenuator. Appears that I also already had grasped the idea of signal overload.

    Also am reception would improve by placing a permanent (loudspeaker) magnet on top of the transistor radio.

    Reply ↓
    1. Bill Hemphill

      Bert,

      Your using the ground reminded me of my experience with the toy type crystal radios. I had found that if I clipped the antenna lead to the ground side of an electrical outlet, then I got great reception of the local stations. This was in the days of non-polarized electrical plugs. If I remember correctly, the left prong of the outlet was usually ground and is what I normally used. But at school one day, I tried it and turned out the left prong was hot and I shorted it out with the outlet cover plate. It sparked and melted the antenna wire alligator clip. So much for listening to the World Series that day in class.

      73
      Bill WD9EQD
      Smithville, NJ

      Reply ↓
      1. Bert

        One day my school buddie’s younger brother asked me to fix his crystal am receiver. I corrected his error, gave the ground part wire to the little guy “hold this against the radiator”, gave the antenna part wire to my schoolbuddy “stick this in your mouth”, and i could listen to both of the (then) national am frequencies of the Flevo transmitter site.

        Hard to miss, flevo transmitter was only some 25 km away, 400KW, path over wetlands.

        Now the Netherlands is into private LPAM radio.

        Reply ↓
    1. Martin Tobisch

      Hallo Pedro
      Ja das ist wirklich sehr einfach. Wie oben beschrieben sind diese 8 Windungen auf den Kern zu wickeln und das Koax anzuloeten. Die spule hat eine erstaunliche Fernwirkung. Deshalb ist das Thema Ausrichtung kein Problem mehr. Im Text hatte ich eine Quelle fuer die Ferrite angegeben. die sind erprobt und bestens geeignet und haben einen guten Preis. Das Foto mit dem fast durchsichtigen blauen Isolierband zeigt eigentlich auch das Innenleben. Die Windungen sind gut zu erkennen.
      Viel Erfolg beim Nachbauen und ueberweitere erfahrungen freue ich mich auch.

      Reply ↓
          1. Martin Tobisch

            Hi Dennis
            I guess its not a real magic number. The first test with one or two made very low signals und you have to adjust the coupler exactly. Then i found with 6 cores it works good and stopped further testing. And it was my last ferrite that time hihi. But it is an interesting idea to try it with more than 6 ferrites. Please inform me if you have new results or experience. The linhs for ferrite cores i wrote in the comments are approved. It si NiZn Material and i used it a lot even for EFHW antennas.
            best 73s
            9H1D

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