Grundig Ferrite Rod design

[simpsons]

A conventional ferrite aerial consist of a simple cylindrical rod or bar shaped design upon which the resonant coil is fixed.

From my collection of Grundig radios, the ferrite rod is grooved about the circumference.

Given both Grundig and Philips have, at the top end of the market, produced competitive designs only Grundig use a grooved ferrite rod.

Is there a technical reason behind this?

Chris

[Leon Crampin]

Yes. The resistivity of ferrite is not infinite, despite a very small particle size. An energy loss will therefore occur along the lines of a partially shorted turn.

By grooving the ferrite, the theoretical shorted turn is made much longer - maybe doubled in length, consequently halving the losses from this effect.

Good design again from Grundig - pity about the grease they used in gang shaft bearings, which dries up and causes seizure. No design is perfect though.

Leon.

[simpsons]

Thank you Leon, how interesting.

I wonder why this design is only used on Grundig transistor radios.

I can't find a patent for the grooved rod design which would give me a time frame for its introduction.

For example, the Grundig mains radio such as the 3028 has a simple "thin" rod.

In addition, great play is made by Roberts of their R983, a clone of the Sangean PR D3L and similar to the C Crain CC, of the fat ferrite rod, said to bring in AM stations unheard on lesser sets.

I had one of these and didn't find stations "unheard" but more importantly, the digital display failed. But I digress.

Chris

[Goldieoldie]

Why did manufactures not use ferrite rod aerials on their earlier valve radios ?

[Leon Crampin]

I think Siemens supplied this ferrite to Grundig. In my automotive design work which was active at about the time these sets were designed, I found the Siemens range of ferrites to be more comprehensive and better performing (especially with regard to curie point, critical for engine mounted components) than the offerings from Philips.

The politics became messy though, with the UK military being the final user.

Leon.

The development of suitable ferrites occurred as valves were being replaced by transistors. There were a few valve portables with rods, and my late version KB FB10 has one.

[ajgriff]

Interestingly Phillips EE kits (1960s) had grooved ferrite rods. I've still got mine!

Alan

[Cobaltblue]

Originally Posted by Goldieoldie

Why did manufactures not use ferrite rod aerials on their earlier valve radios ?

Manufacturers would use what was available and cost effective.
Like many developments in electronic design its driven by new materials and processes, unavailable or cost prohibitive to the designers of yore.

Cheers.

Mike T

[paulsherwin]

Lots of valve sets used ferrite rods from the mid 50s onwards.

[Tractorfan]

Hi,
I have a Blaupunkt stereo valve radio that has a ferrite rod aerial within.
It is grooved and mounted on a steerable base controlled from a knob on the front panel.
It is visible on the right just below the speaker.
Cheers!

[Cobaltblue]

The Ferrite rods in the Philips Electronic Engineer kits EE8 and EE20 use these groved rods so its not as Philips were unaware of them.

Cheers

Mike T

[Radio Wrangler]

Originally Posted by Leon Crampin

I found the Siemens range of ferrites to be more comprehensive and better performing (especially with regard to curie point, critical for engine mounted components) than the offerings from Philips.

That was also the view amongst the filter and RF people at HP here.

US SMPS folk went more with Ferroxcube

David

[Leon Crampin]

It's quite possible that Philips supplied Siemens ferrite in their kits. The Philips group frequently ousourced and re-marked items from other suppliers if this was expedient. For instance, I have some Mullard IW4-350 rectifiers that are obviously MOV MU12 devices.

Ferrites for the kits may have been a very small production run compared with the needs of the radio industry.

One thing I found to be irritating concerning Philips and the supply of ferrites for production was that they didn't actually produce some ferrites listed in the data book unless there was significant demand. My application was a small run, and my chosen ferrite tube was not actually produced, despite the fact that they had submitted samples - hence a move to Siemens.

Leon.

[G6Tanuki]

Originally Posted by paulsherwin

Lots of valve sets used ferrite rods from the mid 50s onwards.

Yes, there was a rapid transition from the old-style 'frame' aerials to ferrite-rods in the early/mid-50s valve radios. By the coming of the transistor radio in about 1956/57 everything had gone Ferrite Rod.

[Were there _any_ transistor radios made using old type frame aerials?]

Ferrite 'pot cores' also took over from the older wave-wound coils in IF transformers in the same era; it meant that IFTs could be made both smaller and higher-Q. Oldest radio I have that uses ferrite-pot IF coils [eight of them, with three IF amplifier stages meaning it's rather selective] is my "Reception set R209" military radio whose first version appeared some time around 1945/46.