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I am making a 2 Watt FM transmitter. The transmitter's inductor is somewhat like this :-

enter image description here

The resistor is part of the transmitter circuit. I am little confused with the inductor and not sure how to make it. I have small ferrite toroid. Will it work?

And 0.8mm CuAg wire means 20AWG. If I replace it with #23 or #26 wire, how many turns would be applicable? For L2, would a normal insulated copper wire work? And should it overlap L1 on the ferrite, or co-exist on the ferite beside L1?

I am referring the below circuit:

enter image description here

Any idea, if L1 and L2 can be replaced with a single air-core Copper Coil?

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Actually the inductor in the 2nd schematic is a single core inductor ! Well not really, it is actually a transformer.

The connection to the antenna is part of the inductor. Actually that inductor is a transformer, the primary side has a centertap, the secondary side is connected to that centertap and the other connection goes to the antenna.

It would have been more clear if this symbol was used:

enter image description here

But then without the core ! T1 and T2 connect to top and bottom right, mid-right and bottom left connect to battery voltage, top left is the antenna output.

This is a configuration that is used to connect the differential signal, present at the collecors of T1 and T2, to a single ended antenna.

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  • \$\begingroup\$ Sorry @FakeMoustache I am actually referring this circuit (my bad, I posted the similar circuit by mistake): educypedia.karadimov.info/library/fm2w.gif which is a similar version of the above one and describes 2 lines on the inductor. So is it a regular transformer? I believe, a normal transformer has way more inductance than what is required in a FM transmitter. Isn't it? \$\endgroup\$ – sribasu Jul 17 '16 at 19:13
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    \$\begingroup\$ So is it a regular transformer? What is a regular transformer ?? Maybe you're thinking of a mains transformer ? Of course these need more windings as the operating frequency is a lot lower (50 or 60 Hz). A transformer at 100 MHz (or even 100 GHz) is still a transformer, it might have less windings, it will have less inductance, it might not have a magnetic core. But it is still a transformer. \$\endgroup\$ – Bimpelrekkie Jul 17 '16 at 20:28
  • \$\begingroup\$ The way this new circuit is drawn is confusing as it is unclear from the schematic that there needs to be magnetic coupling from L2 to L1. The bottom connection of L1 is the battery voltage. It has no RF signal. So making L1 a separate coil makes the circuit transmit nothing ! The way the RF signal is fed to the antenna is by the magnetic coupling between L1 and L2, which is invisible in the circuit, making it a confusing drawing. Sure it is mentioned in the text but who reads that ? \$\endgroup\$ – Bimpelrekkie Jul 17 '16 at 20:38
  • \$\begingroup\$ No @FakeMoustache there was no text describing the coil. Unfortunately! That's why I am seeking help. Please can you guide me a little to complete the coil. How to achieve magnetic coupling from L1 to L2 in this case? And yes, I thought it to be a mains transformer. Thanks, you made it clear. \$\endgroup\$ – sribasu Jul 18 '16 at 19:40
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    \$\begingroup\$ How to achieve magnetic coupling from L1 to L2 in this case? Read the textbox, it says: L2 is 2-4 turns of insulated copper wire wound over L1. You wind L1, then you wind L2 over it. \$\endgroup\$ – Bimpelrekkie Jul 18 '16 at 20:55

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