What do you know about electronics? [Apr. 1990--Electronic Servicing & Technology]

Copper wires vs. fiber-optic cables

By Sam Wilson, CET

You hear a lot about fiber-optic tele phone lines these days. They are rapidly replacing copper wires for communications applications. It is interesting to compare some of the features of the two types of communications lines to see whether there is really any advantage of fiber optics over copper.

In this discussion, the term copper conductor means a conductor of electricity; fiber-optic conductor means conductor of light.

Assuming equal weights of fiber-optic and copper materials, the fiber-optic material will produce three times the length of the copper material. Putting it another way, if the two materials cost the same per pound, the cost per 100 foot length of the fiber-optic conductor would be one-third of the cost of the copper conductor.

The fiber-optic conductor will permit three times the data-handling capability. The bit-error rate is a comparison of the number of error bits per total number of transmission bits. For copper conductors, an excellent bit-error rate would be one bit per million. However, the number is usually closer to one error bit in 10,000. For fiber-optic materials, a bit-error rate of one bit per 10 trillion is common.

Whenever there is a bit error in a transmission, it is necessary to take the time to retransmit the signal. That results in lost time and added expense for the company using the system.

Two other important features make Wilson is the electronics theory consultant for ES&T. fiber-optic cables more attractive than copper cables:

• Fiber-optic material has a long life time because of its natural resistance to corrosion.

• Installation and section-replacement costs are less.

The committee syndrome

Lately I have encountered an unusually high number of companies with a frightening method of operation. When I try to get something done in those companies, I am told (very politely): "Everything here is done by committee.

Your suggestion will be taken under advisement by the committee." If you aren't careful, you will miss the real message. Let me rephrase it for you: "We have no leader. No one in this company can make a decision. With the use of committees, it is not necessary for anyone to take the blame if some thing goes wrong.

"There is no one here who has the guts to stand up and say what should be done. There is no one here who has the nerve to say (when necessary), 'I made a mistake and here is what I am doing to correct it.' "Our committee structure protects us from anyone who may want to make a dynamic move. We are protected by the fact that if anyone is hired, the commit tee must first give its approval of the applicant. Thinkers need not apply.

"There is no incentive here for being the best at what you do. Our commit tees are effective in defusing leader-type personalities. We believe in the great mediocre society." It makes me wish we could go back to companies and organizations run by a good old Bull Moose.

Being calculator smart You know from kindergarten that the rms value of voltage (V) can be deter mined from the peak voltage (V,,) by the following equation: V= (0.707)V,, A more accurate value can be obtained using this equation: vA V:(1-si h ,l)V

For average values (VA vE ) when the peak value is known, use this equation: v= (0.636)V,,

To get a more accurate value: V A %It = (2/n)V,, If your calculator is getting old, it may not be able to do the following calculations. Try this simple arithmetic problem: 10-3x3--l=0 My calculator can't handle that one.

Instead of zero I get this answer:

-1x10'°

Try your calculator on this simple trig problem:

TAN 20°=0.3639702

TAN (2 x10^7)°=(should be the same answer)

My calculator drops the last two digits. Errors in these calculations are more likely to occur in older calculators.

Letters

I wish I could include all of the letters that we get, but that is impossible.However, I do try to answer every letter. Sometimes it takes a long time. If you don't hear from me in six to eight weeks, you know that your letter has dropped to level two.

In this issue, I had room for a couple of interesting letters. This one is from

From Pat Cerone, WEZG/WXRA Radio, Clay, NY:

After all of the trouble I went through to build a remote infrared tester, I found that I already had one.

Not only that, but it will check all types of remotes: infrared, sonic, garage door openers, etc. All you need is a small AM radio; aim the remote to the antenna loop and you will hear it loud and clear.

The Editor (Conrad Persson) and I have both tried this and it works! It may be because the remote control is pulsed and that produces a wide range of harmonic frequencies. In any event, it works very well.

We appreciate your sending this good tip and I'm sure the readers will appreciate it too.

Here's a letter from CAMCO Avionics, Long Island, NY:

We at CAMCO Avionics find your quizzes very entertaining, but the answer to question three in the December 1989 issue confuses us. Your voltage is going through an inverting amplifier, so it must be true that the positive input voltage should be negative on the output. Right? The reason the inverting amp is used is that the non-inverting input does not produce a gain proportional to the simple ratio of resistors. Instead, the gain is 1+R1 /R. However, you would not want to be put into a position of saying that 2+4=-6 or any other negative number. Actually, the absolute value i taken to be the answer for summing amplifiers even though the output is, as you indicated, 180° out of phase with the input.

Thanks for taking the time to write.

Unusual diode applications

You have, no doubt, used LEDs as light indicators, but they have some interesting properties not related to giving off light. As far as I know, these properties have never been put to use.

An LED also works, with some limitation, as a light-activated diode (LAD). Its conduction changes when a bright light is directed to it. The LEDs with clear plastic lenses seem to work best as LADs. If you have any practical use for this LED characteristic, don't tell anyone. Send me a letter explaining your idea.

Another unusual feature of the LED is that it behaves like a zener diode. I you have a curve tracer on your scope, connect an LED into it for an interesting test. You have to supply enough volt age to get it to zener on the reverse half-cycle.

I have played around with this concept and I was able to make a shunt regulated supply. However, the zener diode that would do the same job costs less than the LED. Still, it is an interesting idea.