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HB9ABX > TECH 20.07.06 13:10l 43 Lines 1455 Bytes #999 (90) @ WW
BID : J2P840HB9EAS
Read: GUEST DG9VH DG1VV DL1LCA DK2ZA OE7FMI
Subj: re: digital modes
Path: DB0FHN<DB0NOE<DB0GAP<DB0GPP<DB0LX<DB0CZ<HB9EAS
Sent: 060720/1105z @:HB9EAS.CHE.EU [Basel JN37TM] DP6.00 $:J2P840HB9EAS
From: HB9ABX @ HB9EAS.CHE.EU (Felix)
To: TECH @ WW
Klaus, DL8OL is probably not aware of the potential problem
of ground loops. Maybe his is lucky, not suffering this problem,
or he did not notice it, due to low level of appearance.
Besides wrong transmit levels, ground loops are a frequent
source of distorted transmisssion.
In digital transmission, different equipment is connected to
the transmitter, each one having its own power line.
Computer power
TX-power
Controller power and ...
Most equipments have their own protective ground, which
goes together at the power line connection. This way
a closed loop is formed. Normally, there exist a voltage
difference between 2 different power connectors, which then
create a current to flow in the loop. Furthermore, the loop
couples inductively to the fields of all power transformers.
This will create a voltage drop on the ground line of the
Mic line leading to the transmitter, and this voltage is
added to the desired audio signal.
The solution is opening of the ground loop, or other
solutions as audio transformers, opto couplers, or similar.
In any case, after installation, the transmission is to be
monitored by a control receiver to verify the purity of the
signal.
I recommend further study of this problem at the
following locations:
http://en.wikipedia.org/wiki/Ground_loop_(electricity)
http://www.epanorama.net/documents/groundloop/index.html
73
Felix Meyer HB9ABX
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