This Broadcast Electronics FM3.5A is 40 years old. There was a small problem that took the station off the air for a couple of hours this morning. The high voltage shorting solenoid fell apart, causing the 40 amp breaker in the service panel to trip.
These types of failures will become more frequent as the transmitter ages. Things like air switches, blower motors, tuning and loading mechanical assemblies, circuit breaker fatigue, plate rectifiers, screen and plate bypass capacitors, exciter and controller fans, etc. The list of potential failure points can get quite long. The fact is, nothing lasts forever.
There is no backup transmitter for this site and there is no easy way to get a temporary unit on line, if needed. This is not the oldest main transmitter that we service with no backup. That honor goes to a CCA DS-3000 built in 1970.
The question is; how long should old tube transmitters be kept in service? Also; how long should we (an independent service company) agree to maintain them? The temporary solution for the above failure was to remove the broken shorting bar and turn the transmitter back on.
That creates a safety issue for anyone who may need to work on the transmitter before the replacement arrives. It also creates a potential liability issue for my company.
I put a big label on the back door indicating that anyone doing service needs to discharge the power supply capacitor with the grounding stick (which they should be doing anyway). But I will feel better when the shorting solenoid is working again.
I went to do maintenance at one of our sites and noticed that a certain transmitter was running at half power. Followed the path of the fault log and found this. When I mentioned it to the station staff, they said, “Yeah, we noticed it sounded a little funny…”
This is the second time this has happened with this particular transmitter. In any case, this is what I get paid for, so I am certainly not complaining. If only every problem where this easy to find.
When I get back out there to replace this, I will bring out my network analyzer and sweep the antenna and transmission line to make sure there are no issues with that. In addition, I will double-check all the grounding to make sure the copper thieves have not made off with any critical components like the ground buss bar or #2 solid down lead wires.
Bad weather or other disasters can strike any time of year. Around these parts, the most dangerous weather events occur from early spring through late summer. In the past twenty years or so, we have had tornadoes, hurricanes, micro bursts, flooding events and so on. All of that got me thinking about what would happen if a tower came down, or a transmitter building was destroyed by fire, wind, water, etc.
If past events can predict future performance, there would ensue a mad scramble to replace damaged equipment and or get some type of temporary antenna into service. That is what happened in great City of North Adams, Massachusetts when the tower that held the cell carriers, the 911 dispatch, and the local FM radio station came down in an ice storm. Fortunately, we had a single bay Shively antenna at the shop that we trimmed up and installed on a temporary pole with 200 watts TPO.
That will cover the city of license, provided there is electricity…
What if there where an event that was so devastating that the electrical power would not be restored for months? Think about hurricane Maria in Puerto Rico. After that event, the infrastructure was so devastated that there was not even the possibility of getting a fuel truck to deliver diesel for the emergency generators at the hospital in San Juan. It can happen.
With that in mind, I began poking around and thinking about how I would get something back on the air. In the face of massive disasters, AM and FM radio is still the most effective way to communicate with the general public. Radios are still ubiquitous in homes, cars and businesses.
In a short period of time I came up with a couple of solutions. First, the frequency agile Bext exciter uses a single solid state rectifier feeding 24 volts to the power supply board. The audio input includes a mono balanced line level input which can be fed by a computer sound card or some other simple source.
From there +12, +15 and +20 VDC are created to run various circuits. The heat sink cooling fan is the only thing that runs on 120 VAC, which is old and I might replace with a 24 VDC unit.
The power output is about 22 watts, which is not bad. That will certainly get out well enough from a high spot and provide good coverage when the power is out because all the other in band RF noise generators will be off.
Then I though about the deep cycle batteries in my barn. These 6 volt, 435 Ah units have been around for a couple of years, but last I checked, they still held a charge. Other deep cycle batteries from things like golf carts, fork lifts, campers, boats etc could also be pressed into service. The point is, 24 VDC should not be impossible to create.
To keep a charge on the batteries, this solar panel will work:
This setup would require some sort of 24 volt DC charge controller, which I found on Amazon for less than $15.00 US. This charge controller has selectable 24/12 VDC output and also has two USB ports which would be handy for charging hand held devices.
I measured the power draw while the exciter was running 20 watts into a dummy load, it draws 120 Watts.
The final part would be some sort of antenna with transmission line. For this situation, a simple wire center fed dipole hung vertically would work well. This can be fabricated with two pieces of copper wire and a few insulators.
The lengths of each wire can be calculated as follows:
Approximate length in feet: 234/f (MHz)
Approximate length in inches: 2808/ f (MHz)
Approximate length in cm: 7132/f (MHz)
For the FM band, maximum length of wires needed will be 32 inches (81 cm). Insulators can be made of anything that does not conduct RF; PVC, ABS, dry wood, dry poly rope, etc.
I recommend to cut the wires slightly long, then trim little bits off of each end while watching the reflected power meter on the exciter. To keep RF from coming back down the shield of the transmission line, make 8-10 turns, 6-8 inches in diameter of coax as close to the antenna as possible and secure with a wire tie. This will create a balun of sorts.
My emergency FM kit consists of:
Bext Frequency agile exciter
30 feet, RG-8 coax with N male connector on one end
4 ten foot RG-58 BNC male jumpers
1 four foot LMR-400 N male jumper
Dipole antenna, cut long
Solar charge controller
Small basic tool kit; hand tools, plus DVM and soldering iron
Power cords, extension cords
300 watt 12VDC to 120VAC inverter (pure sine wave)
20 feet audio wire
Various audio connectors; spade lugs, XLR male and female, RCA, 1/4 TRS, etc
Various RF connectors; PL-259, N, BNC, etc
Bag of 12 inch wire ties
3 rolls of 3M Scotch 88 electrical tape
100 feet of 3/8 inch poly rope
This is all kept in a sturdy plastic storage bin from the Home Depot. If needed, the batteries and solar panel are stored in the barn along with an assortment of other goodies.
Will it ever be needed? Well, I hope not. However, it is much better to be prepared to restore services than wait for somebody to show up and help. Sitting around complaining about the government does not relieve those people in need during and after a disaster.
This satellite dish nearly broke off of its mount during a “macroburst” event. According to the National Weather Service:
A macroburst is a thunderstorm downdraft affecting an area at least 2.5 miles wide with peak winds lasting 5 to 20 minutes. The macroburst is a straight-line wind phenomena not associated with rotation…used to differentiate from tornadic
winds. Macrobursts can produce as much if not more damage as tornadoes due to the size and scope of a macroburst.
On May 15th a large group of severe thunderstorms triggered at least three tornadoes and one macroburst event in eastern New York and Western Connecticut. Winds in the macroburst area were estimated to be in the 85 to 105 MPH range.
The next morning, it took a long time to get the the clients studio. Trees where down everywhere, roads were closed, traffic lights not working, etc. This created numerous detours and traffic jams. When I finally arrived at a clients studio facility, this was the first thing I noticed:
That is an older 3.8 meter comtech dish hanging on by one 3/8 inch stainless steel U bolt. The funny thing is, they did not complain about this or the lack of satellite service. The main complaint was that the studios were on generator and some of the lights and air conditioners were not working.
This dish had originally been put up when AMC-8 was the main commercial radio network bird in the US. The dish elevation was only 9 degrees above the horizon, so this had to be put up next to the building at roof top level to clear the trees and see 139W.
I was attempting to secure the dish but in the end, the 650 pound dish was too tenuous and the weather was still unstable. There was other damage to the dish thus we decided to take it down instead. Even that took a bit of doing. We were trying find a crane or bucket truck, but all that type of equipment had been pressed into service with recovery efforts. We finally undid all the bolts and bracing and fell it like a tree.
The dish was then cut up and put in the dumpster.
The new satellite dish will be installed next to building in a lower position.