ON5MJ wrote:

hello everybody,

For many years it's a common practice to shortcut the unused part of
inductances in PA, Pi filters, etc, following the selected taps on the coil.
We can consider that the shorted turns are in fact the shorted secondary of
a transformer coupled to the primary made by the "hot turns". Consequently
this would dissipate power and reduce the Q. Is this right or not ? Or told
another way: is there any inconvenience in not shorting the unused turns ?

Thank you in advance for your explanations and experience.

73 de ON5MJ - Jacques.


I suspect that if one leaves the ends open one either has a problem with
nasty resonances or one has a problem with too-high RF voltages.

The coupling isn't terribly tight, and the coil should be fairly
efficient, so you may not lose that much (but checking it would be a
good idea).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com