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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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