Troubles at the AM tower; I don’t know why, it won’t switch power. Over the phone I can tell, the program director’s day is not going very well. Press the “day” button but there is no kerchunk, the directional coupler shows the load is junk. Out into the big field, I go to find the problem quickly and fix it just so. The wind is cold, the snow is deep, I think of the contract terms I must keep. Reaching the tuning house, take out the keys, lock, do not be frozen, please. Once inside, there I find, no big surprise, the mice have been a working this pre-sunrise. A nest they have build in a most inconvenient place, in the back of the phasor wiring chase. Oh, the wires they have chewed, the circuit’s destroyed, all for the lack of mousetraps deployed. As I reach in to clean out the mess, the smell of mouse makes me gag, I confess. The fuses are blown, the contactor is jammed, perhaps, if I am lucky, I can move it by hand. A large screwdriver strategically employed, I pry up slowly, further damage to avoid. The bar thunks up, the contacts engage, the transmitter is ready to apply amperage. Call on the cell phone, tell them it’s fixed, stand back and watch the base current meter, transfixed. Then; Up it goes! Wonderful radio frequency current flows! I clean up, lock the door, lock the gate, carrying bad news the owner will hate. The damage is grave, the repair bill is steep, if a good relationship with the FCC you desire to keep. Business is off, the accounts are low, is this really necessary, he wants to know. The terms of the license are your obligation to keep, getting caught out of tolerance will not be cheap. Looking forlorn, the owner says in disgust, it is only the AM, but fix it if you must. Happy as a lark, with a song in my heart, I dig though the manual and order the part. Time to go home, eat breakfast, brush teeth, take a shower. I have another client to see before the noon hour.
40 amp RF contactor
Dedicated to all those who have been there, done that and the breed of RF men and broadcast engineers who are slowly fading away.
Here in the northeast, there are seasonal variations in the types of weather phenomena encountered. Blizzards in the winter, severe thunderstorms, and the occasional tornado in the summer, at least that is the way it normally happens. This year, we have already had two thunderstorms and a stretch of unusually warm weather. My highly advanced personal weather prognostication technique consists of looking at trends, and the trend thus far this year is warmer with more storms.
Weather Radar, thunderstorm line
When the weather RADAR looks like this, it is too late.
To that end, it is time to go around and check all of the grounding and lightning suppression methods at various transmitter sites and studios. I would rather spend a few minutes extra now than get called out in the middle of the night for an off-air emergency related to a lightning strike.
Proper grounding of all equipment, RF cables, and electrical service entrances is the minimum standard for transmitter sites. Proper grounding means a common point grounding system connected to one ground potential.
To that end, all coaxial cables that enter the building need to have their outer shields bonded to the site grounding system at the base of the tower and the entrance of the building. With an FM station where the antenna is mounted at the top of a tall tower, the coaxial cable outer jacket acts as an insulator along the length of the tower. A lightning strike on the tower will induce a very high potential on the outer conductor of an ungrounded transmission line. After entering the building, the lightning surge will find the next path to ground, which will likely be a coax switch or the transmitter cabinet. Neither of those two outcomes is desired.
Thus, it was time to ground the transmission lines at WRKI, the FM transmitter we moved last January.
3 inch coaxial cable grounding kit
Fortunately, Andrew, Cablewave, Dielectric, and others make grounding kits for various size coaxial cables. They are very easy to apply and make a solid connection between the outer conductor and the site ground.
3 inch coaxial cable grounding kit
The kit contains a copper band bonded to a ground wire, stainless steel clamp, waterproofing, tape, and a pair of bolts.
3 inch coaxial cable properly grounded
The concept of transmitter site grounding is pretty simple and inexpensive to implement. Thus, it is surprising to me how many transmitter sites, especially older sites, do not have adequate grounding. That is an accident waiting to happen.
Back last February, it was reported that FEMA/Department of Homeland Security was mysteriously constructing prepackaged AM transmitter buildings at various PEP (Primary Entry Point) transmitter sites across the country as something call “Primary Entry Point Expansion.” These buildings contain a 5 KW Nautel AM transmitter, EAS gear, satellite equipment (the exact equipment list is undisclosed), and a backup generator all in a shielded (Faraday Cage), prefabricated building placed inside a fenced-in compound at the station’s transmitter site. The buildings are being put in place, but not connected to anything in the outside world. They are planning to have about 80 (the number keeps increasing) of these structures in place by when the project is completed in mid-2013.
FEMA/DHS IPAWS PEP expansion project
Why, inquiring minds want to know, would they do that?
The new buildings and equipment are, of course, not provided to the government for free. I would estimate each unit costs at least $200,000 based on the following:
A new solid-state 5 KW AM transmitter costs $50-55K
A new 35 KW generator costs $23K
A new, shielded communications structure costs $70-85K
Those prices are roughly what a private company might pay, the government procurement costs would be higher. Multiply by 80, which equals at least $16M, perhaps double that when project administration is considered. In the distant past, through something called the Broadcast Station Protection Program (BSPP), FEMA did provide generators, fuel tanks, transfer switches, and occasionally a bomb shelter to key EBS stations throughout the country. In the recent past, FEMA and the government, in general, have been reluctant to fund even mandated changes in the EAS system, first in 1997 when EAS was first implemented and again in 2011 when the CAP modifications were required. Why are they now spending at least $16M to provide EMP-hardened facilities forAM radio stations?
The rationale for this current wave of government spending, as reported in several industryperiodicals, is simply a matter of supplying in-depth backup facilities in accordance with Executive Order 13407. The design of the structure and manner of installation seems to indicate the primary concern of FEMA is some type of Electromagnetic Pulse (EMP). If an EMP were to happen and it took out the station’s main transmitters, these could be connected to the existing antenna system and switched on. They would provide emergency programming and interface directly with FEMA’s IPAWS (Integrated Public Alert and Warning System).
The interesting thing about this is that there is a coincidence with the upswing of solar cycle 24. Back in 2008, likely when this project was likely first dreamed up, the predictions were for a great number of sunspots in this cycle. That has not happened and in fact, this cycle is now predicted to be the weakest solar cycle since 1823. Even weak sunspot cycles can create problems, but does that warrant supplying 80 backup transmitters, generators, fuel tanks, and buildings to various AM broadcasting stations throughout the country? Further, solar flares and Coronal Mass Ejections (CME) are fairly slow-moving events, the sun is well monitored; alerts would be issued and precautions are taken.
One other thing to consider: HEMP (High altitude Electromagnetic Pulse from a nuclear air burst). AM transmitters are more robust when it comes to HEMP than FM transmitters. This is because of their modulation type and frequency of operation. A 5 KW AM transmitter can withstand RF voltages six or eight times its nameplate carrier rating. Tube-type transmitters are even more robust than solid state. The FM broadcast band falls right in the middle of the HEMP fast pulse frequency (72-225 MHz), which will likely resonate in the tuning circuits of the transmitter exposed to it and destroy all of the active devices. Not so with AM transmitters.
A HEMP event would cause catastrophic damage to the electrical grid across wide areas of the continent (see also; Starfish Prime). The voltages instantaneously induced on computer circuit boards and power supplies would be so high, they would likely burst into flames if they were close enough to the detonation. The same for almost all other electronic devices with circuit boards. It would set the country back one hundred or more years, technologically, causing massive disruptions in the food supply chain. Such an act would surely be met with massive nuclear retaliation by the US. The military has not only hardened all of its communications and command facilities, but they have also undergone rigorous EMP testing, finding and fixing design flaws. Thus, the US military’s capacity to wage war would continue undiminished after a HEMP event, a fact that all other members of the nuclear club are surely aware of.
The case of the blown fuse, or rather the blown up fuse:
Blown 10 amp fuse on Harris SX5 PA board
F32 is blown into small bits and had to be vacuumed out of the bottom of the transmitter. The reason why is the pair of MOSFETs connected to that circuit were shorted. Of course, the reason for the shorting of MOSFETs needed to be investigated. What I found was on the underside of the PA board where the brass stand-off attacked the toroid combiner board, the nuts attaching the stand-off to the combiner board were loose and there was a big arc mark.
I tightened everything up and replaced the MOSFETS, marking them with a pen in case they short again, in which case the drive section needs to be closely examined.
