The recent popularity of a new antenna cable called Skyhighgain Coax has created a safety problem for users and a nightmare for firefighters. SHGC was developed theoretically by Tricenters Experimental Laboratories, Inc. as a signal-boosting element for use in radio and television transmission lines. Scientists at TELI discovered that when a bias voltage is applied to the special material used to make SHGC the effect was incredible. Instead of simply reducing signal loss, the signal strength increased!
Amplification of RF (radio-frequency) signals in the new coaxial transmission cable was actually greater than 3 db (decibels) per meter per meter. (Read that again.)
In laymen's terms, that means that for every 10 centimeters a signal travels through the cable the signal strength doubles! Put 1 Watt of RF energy into one end of a one meter length of SHGC and you get 2 Watts at the other end (assuming you supply the bias voltage, of course). At two meters you get 4 Watts. At three meters the signal strength increases to eight Watts. Doubling the power every meter the total effective power of the signal exceeds 1,000 Watts by the time it has traveled only 10 meters up the line.
Now imagine what would happen if you had a 100-meter SHGC cable. (The actual figures are shown at the end of this article.)
In conventional transmission lines there is always some loss of signal depending upon frequency and the electric characterists of the cable. But with SHGC, instead of a loss, you get a gain in signal strength. This is the stuff every radio engineer has dreamed of.
But here's the problem. The unwary (and mathematically challanged) average user seems to think that if a short section of SHGC inserted in his transmission line is good, then a longer one is better. If one were to, say substitute SHGC for the complete run from their radio shack to the top of their tower, the signal would have more energy than the cable (or the antenna) could withstand. (The 20-meter traps on the tri-band beam that used to be on the 60-meter Rohn 25g tower behind the house in the photograph above were never found.)
Designed to be used in short sections between standard coax and the antenna, SHGC is not currently available, pending the resolution of certain limiting manufacturing capabilities. Some reports have surfaced however that a few samples of the hot-pink colored coax have somehow slipped past reality checkpoints and made their way into the Amateur (and amateur) community. And without official spec sheets and installation guides SHGC poses a significant hazard to the uneducated.
The following table dramatically illustrates the danger of using too much Skyhighgain Coax in any transmission line.
Length of Coax / Power Output
As you can see, by the time you reach only 20 meters, the signal power has exceeded a million Watts! Assumming your facility's commercial power mains could handle the load, the signal would exceed 30 million Watts at only 25 meters from the transmitter.
Of course, most power main breakers would trip long before the million Watt level, but once the signal starts up the transmisison line the peak envelope power (PEP) climbs so fast that there is a possibility that the circuit breakers would either fuse or the electric current would simply jump the breaker's open switch gap and power would continue to increase until the primary main lines evaporated in what could only be described as an artificial bolt of lightning, showering every surrounding structure in hot plasma and sparks.
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