First Radio to use a Ferrite Rod Antenna

Hello all.

I recently restored an RCA 1R81 radio from about 1951. I was surprised to find it uses a ferrite rod antenna. I wonder what is the earliest examples you have with a ferrite rod antenna.

To thank the Author because you find the post helpful or well done.

You have asked an interesting question. Nearly five years ago I wrote an article about different antennas and what they do, but this is in German. Hopefully somebody can use my thread and translate it by using also the pictures. I moved your question to the model page you mentioned because there one can see a picture of that ferrite rod antenna.

You are right that the RCA model 1R81 from 1950 is at least one of the early broadcast receiver using a ferrite rod antenna. In the book "Radios von gestern" (page 66, see also pages 70, 137, 321 and 364) I wrote that Hilpert invented ferrite core in 1908 (patent). Some claim that was in 1909 when Siegfried Hilpert (1883-1951) publically announced that relative resistance would be large in magnetic materials created mainly from iron oxide, and that such materials would be suitable for high-frequency applications. But he never developed practical materials at the level necessary for high-frequency applications.

By the way, magnetite (Fe₃O₄) was fount more than 2000 years before in Magnesia, Asia Minor! The Chinese used Lodestones  (magnetite) long before the Arabs and the West. The earliest Chinese literary reference to magnetism occurs in a 4th-century BC.

Wikipedia for Lodestone: "Based on his discovery of an Olmec hematite artifact in Central America, the American astronomer John Carlson suggests that "the Olmec may have discovered and used the geomagnetic lodestone compass earlier than 1000 BC," thereby predating "the Chinese discovery of the geomagnetic lodestone compass by more than a millennium". Carlson speculates that the Olmecs, for astrological or geomantic purposes, used similar artifacts as a directional device, or to orient their temples, the dwellings of the living, or the interments of the dead."

In Germany, Hans Vogt used the material as ferrite core antenna from 1933 with the name Ferrocart. But it was not common at that time and you could see active antennas, turning drum antennas inside a radio like the French brand Capte used and some American brands etc.

Wikipedia tells us about the ferrite magnet: "A ferrite is a type of ceramic compound composed of iron oxide (Fe₂O₃) combined chemically with one or more additional metallic elements^. They are both electrically nonconductive and ferrimagnetic, meaning they can be magnetized or attracted to a magnet. Ferrites can be divided into two families based on their magnetic coercivity, their resistance to being demagnetized. Hard ferrites have high coercivity; they are difficult to demagnetize. They are used to make magnets, for devices such as refrigerator magnets, loudspeakers and small electric motors. Soft ferrites have low coercivity. They are used in the electronics industry to make ferrite cores for inductors and transformers, and in various microwave components. Yogoro Kato and Takeshi Takei of the Tokyo Institute of Technology invented ferrite in 1930."

Well yes, Prof. Takeshi Takei presented a paper at 57th General Meeting of American Electrochemical Society in St. Louis. That same year, Takei applied a patent for his discovery, which was granted in 1932 (Japan PAT-98844). We should not forget Dr. Yogoro Kato who worked with Prof. Takeshi Takei.  In 1935 TDK Corporation was founded to commercialize this invention.

TDK started mass production of ferrite cores in 1937 under the product name of “Oxide Core” and this was mainly used for local oscillators, mixers and IF transformers for military radios.

But the use of ferrite for antennas is an other story ...
This starts probably with philips in the 1940s. But the general usage started around 1950 for "our type of radios" for broadcast reception., having an impact in about 1953, with often turnable antennas. But we have to know that TDK expanded the usage of ferrite to military radios as well as radio receivers, television receivers and direction-finding antennas for aircraft around 1940.

Philips received ferrite cores from TDK with related technical data on the material after 1940. But then Philips researcher Dr. Jakob Louis Snoek (1902-1950 car accident in the USA) did outstanding contributions to the later growth in ferrite applications - Vervey did theoretical work. Snoek also found the feasible frequency range for the use of ferrite, the so-called “Snoek Limit”. And he developped Ni-Zn ferrite and Mn-Zn ferrite and made related discoveries.

But his start for ferrite took place in 1933 when he studied Hilpert's work from 1909. Snoek actually noticed when removing carbon and nitrogen from iron and iron alloys he could reduce the hysteresis losses. That was in 1937 and lead to the material Fernico and Fernico coils of 1939 and from 1945 invention, 1946 (product) to (soft) ferrite coils from Philips. In 1950 Snoek went to Horizon Ltd. in Cleveland, Ohio. By 1948 Mr. Went led the ferrite research for Philips. 

Since 1944 Jonker and Van Santen worked on materials with the same crystal structure as Perovskiet (CaTiO₃).

Neél invented the theory on ferrimagnetism (not ferromagnetism) in 1948 and was granted the Nobel Price in 1970 for this. In 1947 Philips achieved a cross-license agreement with Western Electric which even lead to an exchange of early patents of WE on transistors. In 1951 A. L. Astuijts found a sintering process which improved teh alignment further by having a much higher saturation magnetization which lead for instance to very strong permanent magnetic loudspeakers. Today we know extremely good hard (for instance from Ugimag, France) and soft ferrites for many applications including hard disks.

Under the term ferrite core we learn at Wikipedia: "Ferrite rod aerials (or antennae) are a type of Small Magnetic Loop (SML) antenna very common in Broadcast band transistor radios (although they began to be used in vacuum tube ("valve") radios in the 1950s; they are also useful in VLF receivers, and can sometimes give good results over most of the shortwave frequencies assuming a suitable ferrite is used). They consist of a coil mounted on a ferrite core (a rod perhaps several inches longer than the coil, but potentially over 3 feet long). This core effectively "concentrates" radio waves to give a stronger signal than could be obtained by a simple wire antenna of comparable size, although still not as strong as the signal that could be obtained with a good outdoor wire aerial.

Other names include loopstick antenna, ferrod, and ferrite-rod antenna. "Ferroceptor" is an older alternative name for a ferrite rod aerial, particularly used by Philips where the ferrite core would be called a "Ferroxcube" rod (a brand name acquired by Yageo from Philips in the year 2000). The short term ferrite rod sometimes refers to the coil-plus-ferrite combination that takes the place of both an external antenna and the radio's first tuned circuit, or just the ferrite core itself (the cylindrical rod or flat ferrite slab)."

To thank the Author because you find the post helpful or well done.