Hello Lech and all


lining the antenna tuning house with screening is about standard in LF/MF
transmitter installations.

Screening of all six sides serves several tasks:

provide short and low impedance return current paths for the matching
circuit.

prevent EM fields couple into the coils and interconnecting wiring (inch
class copper tubing).

prevent losses from humid building material when exposed to high EM fields
associated with the matching circuits

provide protection for humans from effects in high EM fields associated with
the matching circuits


Some antenna tunng houses are lined with aluminium sheets (DHO38
installation in Ramsloh, 23k4), most others are lined with cooper sheet
material.

Copper sheets have the benefit that the material is electrical compatible
with copper conductors and can be soldered for good electrical continuity.

Aluminium sheets are cheaper by themselves but need surface treatment
(Alodine treatment) for making good electrical contacts.

If it where just the inductors, which need screening, then a minimum spacing
from coils to screen equivalent to coil diameter should be provided for
both, to keep edy-currents in the screening under control, and to keep
capacity to ground under control. Lining the whole building serves all tasks
outlined above at moderate cost and optimum performance.

-----Original Message-----
From:   Lech Laszkiewicz [SMTP:[email protected]]
Sent:   Sunday, January 14, 2001 8:49 PM
To:     RSGB LF Reflector
Subject:        LF: coil screening/TA test/ DECCA TRANSISTORS

I wonder why a very highly professional designers of the Decca system went
to the expense and complexity of copper sheet screening of the interior of
their complete buildings containing the antenna tunung/loading coils.
They
seem to have obtained considerable advantages doing so, inspite of the
dissertation of a certain homegrown "Guru". Could it be that the measuring
systems and instruments they used were all wrong?