Toroidal Ferrite Core 18mm Diameter EMC Inductor Coil Form RFI Choke

This is one item of unused medium Q toroidal ferrite core with an 18mm outside diameter and an inner hole diameter of 8mm. The higher pack quantity options are cheaper per unit. They are suitable for a variety of radio filtering and suppression purposes where you don't actually want a particularly high Q factor.

In the test winding shown there are seven turns of PVC covered 1 X 0.6 untinned copper wire in parallel with a 1000pF capacitor. When driven from an RF source via a 1M resistor, the tank peaked at 996 kHz. The -3dB points either side were at approximately 979 and 1018 kHz indicating a middling Q of about 26 at that frequency. Based on this, L = 25.5uH for that seven turn winding.
A more recent test with an antenna analyzer shows very similar results as seen in the pictures.

That is all the information that I have on the material.

Outside diameter: 18mm
Inside Diameter: 8mm
Height: 5mm

As a usage example, in one of the pictures I have used five slightly larger type of similar ferrite grade cores threaded onto my car aerial lead to successfully reduce ignition and fan blower noise on AM radio, though you should be aware that standard aerial plugs will not fit through the hole on this smaller size of toroid. You'd have to cut the plug off and re-fit one. You need to wrap tape around them afterwards to avoid them rattling around and chafing. You can also add them to the power and speaker wires if needed where several turns are possible on each core. There may be small chips where the core has been ejected from the mould.

These came from Lithuania several years ago and are of 1980's Soviet manufacture.

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