Re: [IRCA] [DXFlorida] Computer noise in connected receivers.

[rscotka@xxxxxxxxxxxxx]

It might be possible to try snap over ferrite chokes on the 
connecting cable or wrap it through a core. When I found that my cell 
phone charger pumped noise into my Grundig portable sitting nearby I was able to 
wrap the charger cord through an Amidon 75 material core and got
rid of the offending hash produced. I would imagine anything with an
initial permeability of 850 (Material 43) or higher might do, that's
what the Radio Shack clip over chokes are made of...you'll notice that
most modern era monitor cables have built in chokes to keep noise down
but many higher performing video cards in conjunction with the occasional
oddball modeline will swamp them. My current monitor/card combo wipes my
entire house out though you are on the right track with the older laptop,
I don't get as bad interference from my old Thinkpad 380D when pressed
into service as a thin client around the house....


Russ Scotka






On Wed, 6 Jul 2005 03:39:12 -0400 (Eastern Daylight Time)
"WWWR" <WWWR@xxxxxxxxxxxxx> wrote:

> A while ago I asked here about noise generated by LCD versus CRT displays
> and got several responses which related experiences and offered suggestions.
>  With that valuable insight, I began to think what I wanted to do to
> implement computer control on my receiver.  
> 
> Years ago I had tried it with a desktop computer and CRT which introduced so
> much noise I gave up.  At the time I had a poor, indoor antenna arrangement
> which didn't help any either.
> 
> Considering my options, I remembered a decade old laptop, put aside when no
> longer needed for work.  I decided to try that as a bottom-line benchmark
> for what I might expect.  I had some equally old control software -- DOS
> based Scancat Gold (Anyone remember that?) -- which would be more than
> adequate to evaluate the concept, if not actually provide a solution. 
> 
> I moved the laptop around the receiver and found that a couple feet away
> there was little problem with noise pickup from the computer and monochrome
> LCD display.  Pleased with that result, I connected to the receiver RS-232
> port.  A raucous cacophony broke out.  Clearly this laptop was not going to
> be usable.
> 
> After some thought, though, I had an idea.  The noise was obviously passing
> through the interconnecting cable.  Breaking the electrical connection while
> still maintaining the communications connection seemed a viable solution.  I
> grabbed my Google and began looking for RS-232 optical isolators.  I found a
> few that seemed to address my situation, and settled on one that was
> reasonably priced.  In went my on-line order.
> 
> An optical isolator inserts a light path into the electrical path.  The two
> sides of the connection are electrically separate, while through the light
> beam, signal transfer is achieved.  This eliminates ground loops and other
> sources of transferred noise.  Just what I needed, it seemed.
> 
> A few days later the isolator arrived thanks to UPS and I rushed to test my
> theory.  It seemed sound, but since it  involved a null modem style
> connection between computer and receiver, I had a slight concern that might
> somehow be incompatible with the isolator.  The notion noise might still
> seep through was also still a possibility, not to mention that my whole idea
> was bogus and nothing would pass through at all, not even noise.
> 
> I am very glad to report that the idea was not bogus and I may just have a
> fairly cheap -- under $85 for the isolator -- solution to my computer
> control objective.  Now I know -- should I decide a more elegant solution is
> desired involving added expenditures for a newer computer or more
> sophisticated software -- I can rest assured any expenditures will not be
> lost to a noisy connection.
> 
> If when connecting computer and receiver, a noise level increase is noticed,
> this solution might be worth looking into.  The noise may be squeals and
> squawks created as computer functions are performed, or just an increase in
> the usual background hiss. Which and where the noise manifests itself may be
> possibly isolated at places on one band, or changing on different bands. A
> little experimentation will quickly show if the connection is the source of
> any induced noise.
> 
> I hope my experience may prove of value to others.
> 
> W. Curt Deegan
> Boca Raton, (Southeast) Florida
> [JRC NRD-535D; IBM ThinkPad]
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