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PA2AGA > HDDIG 01.01.00 09:35l 247 Lines 7702 Bytes #-9630 (0) @ EU
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Subject: HamDigitalDigest 99/324G
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I will try to answer any questions, please don't hesitate to e-mail me.
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Before you buy.
>.
------------------------------
Date: Fri, 24 Dec 1999 10:56:23 -0500
From: "Dan" <dan.jaume@usa.net>
Subject: FS: PK232 TNC
FS: PK232 TNC, cables, manual, clean, non smoker.
$ 75.00, shipping included, lower 48 sstates.
Dan 561 286-7241
>.
------------------------------
Date: 19 Dec 1999 00:46:34 GMT
From: haynes@alumni.uark.edu (Jim Haynes)
Subject: ground loops and audio isolation transformers
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: Sun, 19 Dec 1999 10:20:42 -0500
From: "Rob" <NoEmail@NoWay.com>
Subject: ground loops and audio isolation transformers
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: Sun, 19 Dec 1999 13:36:15 -0500
From: "Bob Lewis" <aa4pb@erols.com>
Subject: ground loops and audio isolation transformers
Just curious. When you have the ground loop problem are the radio 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: Sun, 19 Dec 1999 23:10:43 -0600
From: "George T. Baker" <w5yr@worldnet.att.net>
Subject: ground loops and audio isolation transformers
Interesting, Bob.
When I was using my laptop for PSK31, I did not observe any problems with
hum, noise, or instability. But, when I got a new P3 500 MHz system for
the shack and hooked it up to the rig, I could see spurious activity on
the unmodulated carrier on the Monitorscope. Transformers in both audio
lines removed it completely. Like most things involving computers, it is
easier to just "do it" as a precaution and eliminate the source of the
problem than it is to diagnose it and find out what is really causing it.
My IC-765 uses separate returns ("ground") for the mic input circuit and
the PTT circuit. That may be involved with the desktop rig while it did
not enter into the picture with the laptop, although the connection to
the rig was the same in both cases.
I am getting a new Kachina tomorrow - if UPS doesn't self-destruct! - and
it will be very interesting to see how it interfaces to the computer.
They bring out the audio and control lines to a dedicated connector and
the levels are such that no attenuation is required. I will probably go
ahead and install transformers anyway since I already have them and they
seem to do no harm.
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
Bob Lewis wrote:
>
> Must be related to the rig's mike input circuit in some way I guess.
> I've used two different computers and two different lap tops with two
> different rigs (Icom and Elecraft) in all combinations, all with
> direct connections and no hum. Or, I'm just lucky.
>
>.
------------------------------
Date: 19 Dec 1999 23:31:26 GMT
From: Hamish Moffatt <hamish@rising.com.au>
Subject: ground loops and audio isolation transformers
Rob <NoEmail@NoWay.com> wrote:
> I think the main problem may be related to the fact that I use a laptop.
> The laptop has an external power supply with a two prong plug. It is not
> grounded well (like most laptops).
Interesting. How can you detect that you have a ground loop?
I have audio and PTT connected directly from my Toshiba laptop
to my IC-726 rig and haven't noticed any problems.
Hamish VK3SB
--
Hamish Moffatt Mobile: +61 412 011 176 hamish@rising.com.au
To be continued in digest: hd_99_324H
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