Inductor in Series with RF Signal

Thread Starter

Sparky49

Joined Jul 16, 2011
833
Hi all,

My understanding is that an inductor will tend towards blocking an AC signal from passing through it.

I have recently constructed a circuit for a small radio IC (http://www.farnell.com/datasheets/96892.pdf page 17, figure 8) for FSK operation. However, there is a an inductor in series with the output. How does this not block the RF energy? Is it because of the use of a loop antenna, rather than a monopole?

If I were wanting to use a monopole antenna, what would be the best configuration? Simply remove the inductor?

Many thanks for your time,

Sparky
 

nsaspook

Joined Aug 27, 2009
7,350
The inductor and series capacitor form a band-pass filter (and what looks to part of a matching network) to let the fundamental carrier frequency pass while blocking others. No, you can't remove it.
 

wayneh

Joined Sep 9, 2010
16,398
My understanding is that an inductor will tend towards blocking an AC signal from passing through it.
It resists changes in current, yes. But I'm not sure that's a useful way to think about an inductor in all applications. Plenty of AC - all the power entering my house and powering this computer - passes through a transformer, for instance.
 

nsaspook

Joined Aug 27, 2009
7,350
In that case, can I simply use a monopole antenna instead of the loop?

Many thanks for your reply.
Maybe but it's not a simple matter of just replacing it with a random wire if you need to maintain range. The loop antenna forms a component matched tuned circuit optimized to transmit the signal. A proper 1/2 wave dipole or 1/4 wave with ground plane should work but would be the size of a baseball. The loop antenna is physically small but electrically large at the the transmit frequency.

http://ww1.microchip.com/downloads/en/AppNotes/00831b.pdf
 
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