amplifier for MW 520kHz using ferrite core

[earckens]

Would the use of a ferrite core be allowed to be used in the part of the schematic attached, instead of the drawn dipole (with the RF coil ("2F trafo" in schematic) tuned to 520kHz )?

I would attach one end of the coil on the ferrite core to the 100nF cap, and the other coil end to ground.

Purpose is to amplify signals on 520kHz only.

 

[Nigel Goodwin]

Of course, as used in almost every MW radio, with suitable windings to match the aerial impedance.

Usually the main tuning winding is high impedance, and tuned via a large variable capacitor, with a low impedance winding feeding the following transistor. As this is an FET stage you should be able to directly connect the main coil to the FET.

To add an external aerial as well, you simply add another low impedance winding on the ferrite rod, to match the (supposed 50/75 ohm) impedance of the aerial to the tuned circuit.

 

[earckens]

Of course, as used in almost every MW radio, with suitable windings to match the aerial impedance.

Usually the main tuning winding is high impedance, and tuned via a large variable capacitor, with a low impedance winding feeding the following transistor. As this is an FET stage you should be able to directly connect the main coil to the FET.

To add an external aerial as well, you simply add another low impedance winding on the ferrite rod, to match the (supposed 50/75 ohm) impedance of the aerial to the tuned circuit.

So one coil only around the ferrite core is not ok?

Currently I have 72 windings, corresponding to around 500kHz, feeding into the 100nF cap (the first cap on the drawing).

How many windings should the second coil have?

Great info Nigel, on adding the external (dipole?) antenna.

 

[Nigel Goodwin]

So one coil only around the ferrite core is not ok?

For an FET input it should be fine, a bipolar input needs a lower impedance feed.

 

[JimB]

So one coil only around the ferrite core is not ok?

A little bit small, I think.

Currently I have 72 windings, corresponding to around 500kHz, feeding into the 100nF cap (the first cap on the drawing).
How many windings should the second coil have?

I would start with 7 turns for the second winding on the ferrite rod.
ie 10% of the main (tuned) winding.

JimB

 

[Nigel Goodwin]

A little bit small, I think.

I think we read what he put completely differently

The 'coil' is the entire thing, not just a single winding - as I understood it anyway - and he said it was 72 windings.

 

[JimB]

I think we read what he put completely differently

Sounds like another attack of semantic differential!

In JimB speak
Winding = Coil
as in the primary and secondary windings of a transformer.

Turn = a 360 degree circle of wire.

JimB