In article .com,
"bradvk2qq" wrote:

Mike Chambers wrote:
Unfortunately that didn't solve the problem.

The transformer should have fixed the problem. The noise is most likely
coming from the laptop switched-mode power supply. Have you tested it
while running on batteries alone?

I have several radios connected to computers, and for this I use the
Buxcomm Rascal GLX (www.buxcomm.com) and this works for both of my pc's
and my laptop.
The Rascal is also available as a kit for transceivers and you can
build just the receive side if you wish. That said, the transformer
alone should be enough, and there is the possibility that you did not
assemble the cable shielding correctly or add sufficient bypassing.

My computers receive audio, decode it and post it to my webpage. This
system does work, do not despair.

Most likely the switching noise from the laptop passes through the
connecting cable as common mode noise. Try RF chokes on the cable on
both ends.

--
Telamon
Ventura, California

In article ,
John Smith I wrote:

Mike Chambers wrote:
...

Mike:

Here is an interesting link:

http://www.waypoint.com/users/~disco...esentation.htm

One circuit I seen on this page makes use of an opto-isolator. Seems to
me that with a led and photo-transistor one could kludge together a unit
which would seem to perform miracles!!!

The OP already tried a isolation transformer so I don't think an
opto-isolator will be any more helpful.

I expect that it is a common mode noise issue. He can buy common mode
chokes that just clamp on the cables to find out.

--
Telamon
Ventura, California

Telamon wrote:
...
The OP already tried a isolation transformer so I don't think an
opto-isolator will be any more helpful.

I expect that it is a common mode noise issue. He can buy common mode
chokes that just clamp on the cables to find out.


Surely you jest, with optical isolation, there is NO direct connection ...

Unless you are proposing the rf is able to transverse the light beam.

JS

John Smith I wrote:

Surely you jest, with optical isolation, there is NO direct connection ...

Unless you are proposing the rf is able to transverse the light beam.

JS

The optoisolators are only used for ptt keying, not for the audio. The
audio is usually isolated with transformers. But, just because the op
has tried transformers, doesn't necessarily mean he did it correctly.

Brad.

On Wed, 03 Jan 2007 16:02:14 -0800, Mike Chambers
wrote:

I have an Eton E5 which I connect to my laptop via the Line Out on the
Eton to the Line In on the laptop.

This works great for recording shortwave broadcasts, but if the laptop
is plugged in, it generates some interference on the radio (only when
they are connected via lineout / in). If I unplug the laptop, there is
no interference.

Does anyone know if there is anything I can do to get rid of the
inteference? I want to set up my machine to record programs overnight,
so I can't leave the laptop unplugged.

mike

http://mesh.typepad.com

Is your laptop battery weak where it is always charging? This would
overheat the supply and generate more rfi.

We had a Dell with this problem at work. We used to plug the power
supply into a 110 volt isolation transformer and then we connected a
ground lead to the ground side of the speaker jack on the computer.

Another alternative is to replace the laptop power supply with another
brand which hopefully will not be as noisy.

Jim

Telamon wrote:
...
Either one will not be an effective block unless they are designed to
prevent passing common mode RF noise. It takes very little in stray
capacitance or mutual inductance to go around the opto-isolator.


If you are an electronics engineer, I'd venture you are a damn poor one.
The opto-isolation I proposed would be about 10,000x more isolation
than an audio xfmr.

Coupling of rf noise though the audio xfmr is just a question of "how
much?" Indeed, I'd be surprised if they even provided proper shielding
(grounded metal sheet over inner winding with ends of sheet insulated
from each other) of one winding from another!

If the core material is ferrite, like in the cheap china junk, I'd throw
it away for such uses. Silicate-steel laminations might be usable when
rf is a problem ...

Regards,
JS

In article ,
John Smith I wrote:

Telamon wrote:
...
Either one will not be an effective block unless they are designed to
prevent passing common mode RF noise. It takes very little in stray
capacitance or mutual inductance to go around the opto-isolator.


If you are an electronics engineer, I'd venture you are a damn poor one.
The opto-isolation I proposed would be about 10,000x more isolation
than an audio xfmr.

Coupling of rf noise though the audio xfmr is just a question of "how
much?" Indeed, I'd be surprised if they even provided proper shielding
(grounded metal sheet over inner winding with ends of sheet insulated
from each other) of one winding from another!

If the core material is ferrite, like in the cheap china junk, I'd throw
it away for such uses. Silicate-steel laminations might be usable when
rf is a problem ...

You are very weird and you have poor comprehension. Go back and re-read
the thread and you will find that I did not recommend the transformer.
My post of a few lines stated that the opto-isolator would be not any
better than the transformer. I don't know where you get your ideas from
but you are one very confused individual.

The reason another poster thought the transformer would help is because
the problem was created by a ground loop. If the problem was a ground
loop the transformer or opto-isolator would help.

My thinking was always that it was a common mode noise problem with the
switching noise from the laptop getting to the radio through the
connecting cable. A ferrite clamp on core is a good solution. Ferrous
metals are much lower in inductance value than the ferrite and would not
work as well for a similar size core.

Why do you bother to post if you have no idea what you are talking about?

--
Telamon
Ventura, California

I find that it helps somewhat to turn off the screen. I have an iBook, and I can lower the brightness to the point that the screen switches off. Or you might be able to put the screen to sleep while the machine continues to run.

Telamon wrote:
...

In your previous post:
---------------------------------------------------------------------
"I usually don't joke about the subject. The transformer is really no
different than the opto-isolator for DC isolation. One couples primary
and secondary circuits magnetically and the other with photons.

Either one will not be an effective block unless they are designed to
prevent passing common mode RF noise. It takes very little in stray
capacitance or mutual inductance to go around the opto-isolator."

---------------------------------------------------------------------

See the part, "The transformer is really no
different than the opto-isolator for DC isolation. One couples primary
and secondary circuits magnetically and the other with photons."

Why in the hell would we even concern ourselves with dc isolation, it is
rf which is causing the problem ...

Now, see the part, "Either one will not be an effective block unless
they are designed to prevent passing common mode RF noise."

There would be NO coupling, other than a light beam--and I asked you,
are you claiming the rf is traversing the light beam? (and, if so, you
will notice that I implied ONLY AN idiot would site that as being a
problem in this case.)

Optical isolation would be an ABSOLUTE cure for his problem.

JS

Mike,

I had the same issue, and when I first attempted it I clamped it
straight ono the cable and still had noise "BUGGER!!". This is when I
read some where to coil the cable to form 3 loops / turns about 3-4
fingers wide and I clamped two ferrite cores from RS.

That did the trick and the noise is 100% gone.

Hope that helps.

Regards
Mark


Mike Chambers wrote:
Thanks. That didnt seem to help any.

mike

On Thu, 04 Jan 2007 10:47:45 +0100, Charly wrote:

Hello, you can also get some noise-reduction ferrite core, such as this :

http://www.shinemicro.com/images/ferritethumb.jpg

Perhaps you have some already clamped on some device's wire (digital
camera, AC/DC tranformer, modem, etc...).

If you can un-clamp one a clamp it on your laptop power wire OR audio
line wire, just check if it helps...

I did that on my AC/DC adapter of my SW radio, and it helps reducing (a
little) incomming RFI.

Charly