Wednesday, March 21, 2018

Ferrite Antenna data and an example of its use

Ferrite Antenna Data

This article tells the story quite well. A real world example is the DX-160 receiver.
 The Dx-160 is an all band shortwave receiver. It has 5 bands. You can see 5 coils in a row. The alignment process calls for setting The coils at different points on the band. The final step is setting the ferrite antenna coil for each band.
The ferrite rod has a coil for each band. If you read the linked article you will understand the position of the coils effects its inductance. They are wound to be set off center when adjusted correctly.
Here is close up of the coils.

The ferrite antenna on the schematic. (T1 - T5)
The Dx-160 using the ferrite rod antenna
The ferrite rod antenna from the article that I am responding to, it is a tuned circuit being fed by the ferrite. The ferrite is 87uh and the tank coil is 2uh. Coils in parallel that are not magnetically coupled at as resistors do. 87uh in parallel with 2uh = 1.995uh or for practical purposes 2uh. At the other extreme 87uh in parallel with 12uh = 10.7uh. As long as the coils do not magnetically couple you can treat the antenna as a signal source and not a part of the tank. The small amount of interaction would be adjusted out when you tune the circuit. For best results a 10 : 1 ratio or more should be used. The 87:12 ratio is a little to low.

That article also referred to a Small Magnetic Loop.
Here is an example of the small magnetic loop.

Here is the magnetic loop with an amplifier from the same article.No ferrite used here. If this one had a coil on the fet gate and it was equal the loop inductance it would be what the article refers to.

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