oldnewbie said:
Sitting here in Seattle, I watched with interest to the news from Catalina Island. A pretty bad fire, and the news I just heard is that the fire was caused by someone working on a radio station tower. Anyone know any details?
And since I am just learnin' please indulge a few questions that might be obvious to you Professional Engineers.
Is the transmission line from the transmitter to the antenna analogous at all to an extension cord? In other words, how likely is it that a transmission line can be overloaded to the point of causing a fire? What other things at a transmitter site are likely to pose a fire danger? Is there a large difference when it comes to safety between AM and FM and TV? What is the worst safety violation you have seen? AND FINALLY ;-) ... what would be your top safety tip to a newcomer to the business like myself?
Thanks again to all of you. I have learned so much simply by reading this board. I hope the owners don't send me a tuition bill!
Yes a shorted transmission line can cause a fire...I once saw a 9in diameter line with Teflon insulators burn a hole soo big, I could fit my fist through it (obviously after the fire was out
..there is RF (high freq AC) amps and voltage...the rules are still there. Fires are rare if all proper rules are followed but the real world sometimes has faults and doesnt follow the rules
No it is not analogous to an extension cord...just think of it more like BIG coaxial cable (much bigger than your CATV, CB or Ham radio coax cable)...an extension cord would be more like balanced line but thats not used in most modern RF systems (hams use it more on shortwave freqs because of the lower loss at high SWRs or reflected powers than coax). Other things that can cause fires is the electrical feed to the room, the transformers or capacitors shorting or blowing inside the cabinets or anything handling high AC, DC or the RF voltages...AM and TV have similar issues...and there are several possible combinations that cause a failure..if the system is properly designed, there should not be a problem but I have seen failures in line or antennas that were just bad luck or other cause (anything man builds can go bad; nothing is perfect
SAFETY working around high voltage (DC, AC or RF) is ALWAYS the same....you always assume its energized and life unless the breakers are open and the "Jesus stick" has been used to check/drain off high voltage (called such because if you don't use it, you may see Jesus!) Even solid state transmitters have voltages lethal enough to kill, if not seriously injure someone...Once when I was working on a 35KW FM transmitter, a static drain in the Power Amplifier had a ceramic standoff break and the coil then leaned over to touch the high voltage panel which had 10000 volts on it...the standoff broke JUST as I tuned the plates off (I was doing maintenance on it into a dummy load; off air)...heard the "tink" but didnt see anything broke or on the floor....so I hit the Plate On button and BANG!!! all the breakers tipped off while my finger was still on the button Needless to say, my heart skipped a beat as I stood there realizing I was still alive and breathing and nothing was on fire!! I looked at all the breakers and saw all of them (including the AC line) had tripped...then I opened the PA cabinet up, tested for voltages with the Jesus stick and then saw the carbon burns where the arc had occured...30 mins later the transmitter was up and running with no problems (didnt need the static drain as the antenna was DC grounded anyway...so it all came out).
Learn proper respect for voltages and safety rules from a local electrical person (possibly a person at your local power company)...they can show you what happens around 2400 to 35000 volts when equipment fails, etc. Of course lightning or other Mother Nature actions can cause failures in equipment......Zap the lightning god does weird things but there is a madness to the method (or is that method to the madness
Always keep one hand in your pocket (ok thats unrealistic but a rule of thumb always mentioned), NEVER work alone (in this day and age, that will happen more often than not), and NEVER trust noone (ooops Dale Dribble coming through there)...ahhh make that never trust any lead...if it aint grounded, it AINT dead...and you could end being that! In any business like radio where dealing with High voltages, the first mistake you make COULD be your last....
Hope that didnt scare ya off....
BTW my local ABC station just ran a short story on that fire and yes, it was mentioned someone was working on a radio station antenna....will have to do some digging on this
