At 10:27 AM 4/24/97 EDT, you wrote:
>Would a few experts care to help this chap out....and me too? I could
>never find 2 people in a row to agree.
>
>73.....Carl KM1H
>
>I have noticed that some circuits with tapped coils short the
>unused turns and others simply connect the tap leaving the unused
>turns open. What is the rationale for shorting the turns? Does
>the EMF induced in the shorted turns produce a high circulating
>current in the short and therefore energy loss?
>
It depends upon whether you are using a Pi or Pi-L network, and the
number of bands involved. In the early days, simple five band (10-80m)
Pi networks just let the unused turns float. (i.e. the B&W 850 series
coils) Then enter 160m and the WARC bands. At least the 160 meter
portion of the coil needed to be shorted out. When the Pi-L is used
with WARC and 160m taps it is necessary to have multiple fingers on
the bandswitch rotor to short 4 or 5 adjacent taps on the Pi coil.
Extremely high voltages build up on the coil and will crispy-critter
the bandswitch in an instant! Notice on the Ameritrons, Alpha 77
series, and most other Pi-L circuits that there is a special multi-
fingered rotor present on the bandswitch. To answer Carl's question,
probably all the answers were correct, depending on bands and circuit
involved.
(((73)))
Phil, K5PC
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