tapped coils-fm transmitters

[ilektronikos]

why in some cases we receive
the RF signal(in the FM transmiters)
from a tap of the coil(inductor)
like in the schematic (fm);
AND in some cases we conect the
antenna directly to the collector like other circuits;
(fm2)

 

[Nigel Goodwin]

It's to better match the impedances, the output from the collector is really too high to feed the aerial directly, the tapped coil provides an impedance matching transformer.

Connecting the aerial direct is a bit of a 'bodge', but for such a crude device it's often done that way - the tap will also make it more stable!.