Tag Archives: AM Broadcast Antennas

Giuseppe discovers his homebrew rotating ferrite antenna works amazingly indoors and nulls RFI

Many thanks to SWLing Post contributor, Giuseppe Morlè, who writes:

Dear Thomas,

This is Giuseppe Morlè again. First of all, Happy New Year to you and to the whole SWLing Post community! I’ve been continuing the tests on my “T Ferrite” antenna for medium wave and the 160 meters ham meter band.

I tried the antenna inside my shack listening to Rai Radio 1 from Milan Siziano, about 800 km from me, on 900 kHz in the early morning after sunrise. The antenna, despite being inside, proved to be perfect for the cancellation of the electrical noise that I had around me.

Disconnecting the antenna from the receiver–a Sangean ATS-909–the noise occupied everything without being able to listen to anything. Putting the antenna back, the noise disappeared completely making the modulation re-emerge, with a weak signal, it was already day, but with good understandability.

The antenna, as I described in another article, is composed of 2 ferrites 12 cm long each, bought at ham fests, tied together with insulating tape.

For the two windings, I used a small section of cable used for telephone systems that is rigid enough to model perfectly on the ferrites–43 turns for the primary and 3 turns for the coupling link to the receiver. The variable capacitor is 850 pf.

I should mention that the magnificent W1VLF channel was my original source of inspiration for this antenna.

Check out the following video:

Click here to watch on YouTube.

That is amazing, Giuseppe! We often think of magnetic loops as the only choice for coping with urban noise and RFI, but ferrite bars–especially configured like yours–are a brilliant tool for indoor low-band listening. Thank you for sharing! We love your experiments.

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Giuseppe’s homebrew rotating ferrite antenna

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Many thanks to SWLing Post contributor, Giuseppe Morlè (IZ0GZW), who writes:

Dear Thomas,

I’m Giuseppe Morlè (IZ0GZW) from Formia, on the Tyrrhenian Sea, in Italy .

I built this simple rotating directive ferrite antenna for medium waves and the 160 meters ham band.

Inside the tube there are 2 ferrites with 43 cable windings and 3 for the coupling link that goes to the receiver.

In this video the test as soon as I assembled everything …

In broad daylight, it was 12.00 local time, you could hear well over 2000 km.

The antenna is very directive and perfectly manages to separate several stations on a single frequency.

The pipes are in plastic for plumbing use (PVC), I bought only that one, 5 Euros, the rest is all recycled.

I wanted to share this simple and very functional project of mine with the SWLing Post community.

Thanks and I wish everyone a better year.

Greetings from Italy.
Giuseppe iz0gzw.

Thank you, Giuseppe! What a simple, effective antenna project. I like how you’ve invested so little and recycled parts from other projects. I also love your view there looking south over the Tyrrhenian Sea! What a great place for radio.

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Radio World: History of Directional AM Broadcast Antennas

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Many thanks to SWLing Post contributor, Marty, who shares the following article by John Schneider in Radio World:

In the early years of AM radio broadcasting, all stations utilized non-directional antennas. Most all of these were wire antennas suspended between towers or buildings. Interference, especially at night, was severe. An interfering signal of 5% or less in signal strength was enough to disrupt reception of the desired station, and if the frequencies of the two stations were slightly separated, there would be a heterodyne beat note. As a result, only a few widely-spaced stations could operate on each of the AM broadcast channels in the entire country at night. This limited the number of stations that could coexist to about 500 nationwide, with many of them sharing time on a single frequency.

As antenna technologies were developed and improved in the early 1930s, a few progressive stations began experimenting with multi-element directional arrays. This approach offered two attractive benefits: 1) It could reduce radiation towards other stations on the same or adjacent frequencies, permitting more stations to share a frequency; and 2) a broadcaster could direct more signal towards the desired coverage area, and away from wasted areas such as open water in the case of coastal stations.

WFLA-WSUN

The first known use of a directional antenna was by a pair of stations in Tampa/St. Petersburg, Fla. In 1927, the Clearwater Chamber of Commerce acquired station WGHB and changed the call sign to WFLA. A companion station, WSUN, was operated by the St. Petersburg Chamber of Commerce. The two stations shared the frequency of 900 kHz, broadcasting on alternate evenings to promote tourism and business opportunities in their respective communities. In reality, they operated with two station licenses, but there was only one transmitter and one antenna.[…]

Click here to to continue reading the full article in Radio World.

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