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PA2AGA > HDDIG 23.12.99 04:33l 228 Lines 6874 Bytes #-9640 (0) @ EU
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Date: Wed, 22 Dec 99 22:20:37 MET
Message-Id: <hd_99_323C>
From: pa2aga
To: hd_broadcast@pa2aga
Subject: HamDigitalDigest 99/323C
X-BBS-Msg-Type: B
and
> > computer plugged into the same power outlet? How long is the
cable
> > run between the rig and the sound card? I've not had any ground
loop
> > problems but the IC761 and computer are about a foot apart with
only
> > about 2 feet of cable.
> >
> > Rob <NoEmail@NoWay.com> wrote in message
> > news:VM674.199071$5r2.503727@tor-nn1.netcom.ca...
> > > Jim,
> > >
> > > Yes, those audio isolation transformers do a great job when
they
> > are used
> > > right!
> > >
> > > Unfortunately, many people connect one lead of the secondary
and
> > one lead of
> > > the primary BOTH to ground usually INDIRECTLY via a chassis.
If
> > you dos
> > > this, the audio isolation transformer is useless (as you know).
> > >
> > > I have also found that sometimes it is necessary TO COMPLETELY
> > isolate the
> > > ground of the computer from the ground of the rig. To do this,
you
> > MUST
> > > also isolate the ground used by the PTT. Instead of using a
simple
> > > transistor to key the rig's PTT line from the serial port. It
is
> > necessary
> > > to use an opto isolator circuit.. It is really not that much
more
> > > complicated.
> > >
> > > A schematic for an opto isolator circuit for the PTT can be
found
> > at
> > > www.qsl.net/wm2u
> > >
> > > 73'
> > >
> > > Rob
> > >
> > > "Jim Haynes" <haynes@alumni.uark.edu> wrote in message
> > > news:83h9ta$nh3$1@ash.prod.itd.earthlink.net...
> > > > I have found it necessary in several situations that all
happen
> > to involve
> > > > Kenwood rigs to use an isolation transformer when feeding
audio
> > from a
> > > > TNC or computer sound card to the radio. I have used the
little
> > Radio
> > > Shack
> > > > output transformer 273-1380 since it also provides a voltage
> > step-down.
> > > > In the Kenwood mic connector there are two separate grounds,
one
> > for the
> > > PTT
> > > > switch and one for the mic element. I run the transformer
> > secondary to
> > > > the mic element pins only. This has cleared up the trouble
every
> > where I
> > > > have used it.
> > > >
> > >
> > >
> >
> >
>
>
>.
------------------------------
Date: Sat, 18 Dec 1999 11:09:15 -0500
From: "Rob" <NoEmail@NoWay.com>
Subject: ground loops and audio isolation transformers
Thanks George.
Well I am planning to use an opto isolator so my serial port can key my rig
using the PTT line.
The opto isolator should break up the ground loop and isolate the ground of
the computer from the ground of the rig. A good circuit can be found at
www.qsl.net/wm2u/psk31.html
I plan to put the opto isolator circuit, the audio isolation transformers
and my resistor network in a metal box with the metal box connected to the
rig's ground (via the cables from the box to the rigs mic and the rigs audio
output). Of course the shields of the cables from the sound card will NOT
be connected in any way to the metal box BUT DIRECTLY to the audio isolation
transformers. I think this will work okay.
But I will have to make sure that the RS232 cable from the computer is not
somehow grounded to the metal box -- That may be tricky! I assume that is
what many HAMs choose to ground the metal box to the computer (via the
shields of the cables (including the RS232) cable to the computer) and
connect the cables from the metal box directly to the rig (making sure there
is no ground connection to the metal box).
But I think it is better to use the same ground as the rig for the metal box
(NOT the ground of the computer) since there will likely be less RFI
problems (as the ground or lack thereof of my lap top is not great!)
73
Rob
**VA2FB**
"George T. Baker" <w5yr@worldnet.att.net> wrote in message
news:385B1C88.8954F49E@worldnet.att.net...
> It doesn't matter where on the cable the transformer is inserted. But, be
> careful that you do not have any other connections between the computer
> and the rig. A common error/oversight is to use the transformers,
> properly installed, and then add a PTT circuit controlled from a serial
> or parallel port. This automatically connects computer ground to rig
> ground and nullifies the action of the transformers. Another good reason
> to use VOX if your rig will support it with PSK31 or whatever.
>
> 72/73, George
> Fairview, TX 30 mi NE Dallas in Collin county
> Amateur Radio W5YR, in the 54th year and it just keeps getting better!
> R/C since 1964 - AMA 98452 RVing since 1972
>
>
> Rob wrote:
> >
> > I have some ground loop problems between my rig and sound card. I
currently
> > use two resistor networks to reduce the audio levels. (one for the line
from
> > the sound card speaker out to the rig mic input and one for the line
from
> > the rig aux audio out and the sound card mic input)
> >
> > I would like to use some audio isolation transformers on both audio
lines
> > (I,e. the line from the sound card speaker out to the rig mic input and
the
> > line from the rig aux audio out and the sound card mic input)
> >
> > Does it matter where I place the audio isolation transformers on these
two
> > lines? e.g Can I place it on the side closer to the sound card with the
> > resistor network on the other side of the transformer closest the rig??
Or
> > should it be vice versa?
> >
> > 73's
> > Rob
>.
------------------------------
Date: Mon, 20 Dec 1999 21:17:58 GMT
From: Dale Gillilan <positivechanges.hypnosis@gte.net>
Subject: Help: MFJ Multicom on HP200LX
I'm running an MFJ 1289 tnc and using an HP 200lx. It works fine if I
use a simple terminal program (like the one build into the palmtop). I
am able to send commands to the tnc, etc. and everything works.
However, when I try to use Multicomm (or, Baycomm), it does not seem to
communicate with the tnc. I do get data coming back from the tnc (such
as received info), but if I try to send any command to the tnc, it hangs
up my pc. I have tried reloading the software without any benefit.
Does anyone have any suggestions as to what may be going wrong and what
to do about it? I'm totally out of ideas and getting desperate.
Thanks,
Dale
>.
------------------------------
Date: Mon, 20 Dec 1999 16:18:35 -0600
From: Jeff Johns <jeffj@scott.net>
Subject: Help: MFJ Multicom on HP200LX
On Mon, 20 Dec 1999 21:17:58 GMT, Dale Gillilan <positivechanges.hypnosis@=
gte.net> wrote:
> Does anyone have any suggestions as to what may be going wrong and what
> to do about it? I'm totally out of ideas and getting desperate.
To be continued in digest: hd_99_323D
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