Jean-Francios,
Congratulations on identifying and resolving the ground loop problem.
For those situations where a separate power supply is either required or
desirable, the use of an optoisolator instead of the more simple
transistor PTT/KEYING arrangement can also cure the ground loop
problem. However, one must be careful not to unintentionally power the
optoisolator in such a way to make that 'sneaky' gound loop path
re-appear. In most cases, the optoisolator should be powered from the
same supply that powers the device on the 'transistor' side of the
optoisolator.
73,
Don W3FPR
Jean-François Ménard wrote:
Hi everybody,
Since my first prototype of the K2 DATA port implementation, I did
some extensive test today during an outdoor portable operation.
I found that ground loop can occur on lower band... 40m or lower...
And the problem come from the PTT line that goes to ground during
TX. Even if the line IN and OUT are both isolated with an audio
tranformer.
I also test today my DATA port with my SCS PTC-IIe modem and had the
same problem.
I finally found the problem and solved it !!
Like SCS (PTC-IIe manufactuer) said in their user manual. If you
tranceiver have an external power option, like found on Yaesu FT-8XX
data connector, YOU SHOULD USE IT. Do not power your modem from
another power source, but from the transceiver port itself. Like for
the NUE-PSK, PTC-IIe or any other TNC... always power your device with
power from your transceiver.
This way, you will avoid ground loop that will harm your signal
quality for sure.
I just add one wire inside my K2 to the DATA port. I took the 12V line
from the AUX 12V connector inside the K2. This way, you will not have
any more problem and finally have an universal DATA port ffor almost
any kind of external device.
I will post a revised schematic on my website this week.
Like my previous modification, I always use RG-174 for inside wires.
It does prevent RF pickup during transmit and keep the signal as clean
as possible.
I will also post a few more pics.
Another tip, apply acrylic coating spray on the back of the amplifier
board before applying the two way tape. It will prevent short circuit
with any electronic part with the chassis.
Best 73,
de J-F VA2SS
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