Fig. 1: This flashover damage to transmission line was caused by a hunter. Do you ever get grief for “visiting the transmitter site”?
I don’t know what managers think goes on out there; but more than once I got eye-rolling when I announced we’d be working there for the day.
Photos of your maintenance efforts help, especially when they are posted in the lunchroom for everyone to see.
Keep air dielectric line pressurized and moisture-free for reliable operation of FM and high-power AM facilities. If you let a nitrogen tank go empty or fail to repair dehydrator, condensation may form inside the line, with a resultant flashover.
A hunter used the lines shown in Fig. 1 for target practice; whether the damage is from a hunter or moisture, arcing makes for an ugly day for the engineer.
To the right in the photo is the upper connector, cut from line that burned. The lower connector was pretty well ruined.
Note the soot on the Teflon insulation. Rigid line usually can be disassembled and cleaned by passing rags wet with alcohol through them, inspected and reassembled. But the ridges in flexible line, plus the inability to remove the center conductor, may render the line scrap when damage as shown in Fig. 2 occurs.
Fig. 2: Soot is nearly impossible to clean from flexible lines. So check the nitrogen pressure on a regular basis. Invest the few hundred dollars in a low-pressure alarm switch that can be tied to the remote control and installed on the transmission line to warn of a low-pressure condition. Even some positive pressure in the line is helpful. The point is not to let pressure drop to zero.
If you maintain an older transmitter with no VSWR protection, another investment is an RF power monitor. Bird and Coaxial Dynamics offer these. When interlocked into the transmitter, they will shut the transmitter off when an arc or other high VSWR condition occurs. Transmitters without this protection can turn into virtual arc welders once a fault begins.
Thanks to Rich Hill at the Citadel Carlisle, Pa., cluster for sharing the damage pictures.
* * *
Organize your tools and keep them organized. This practice makes for improved efficiency, especially when you’re under the gun to get a critical piece of equipment back online.
Fig. 3 shows a nice labelling job by Transmitter Supervisor Ken Sleeman of Bonneville’s WTOP in Washington. Every tool has its place in the appropriate drawer.
A tool drawer/chest doesn’t have to be expensive. Discount builder supply stores offer a variety of sizes and styles, and some are upgradeable to grow along with your tool requirements.
* * *
Fig. 3: Organization of tools can make a great impression on your manager. Well, after hundreds of Workbench columns, I should have known readers would spot the use for that old clunker relay shown in Fig. 1 of the Nov. 5 column. Sure can’t fool you!
Of course, it’s a poor man’s power failure detector. The AC plugs into a non-UPS fed outlet, and the contacts are wired to a remote control status input.
But what if you don’t have a UPS on your remote control? That’s where other readers picked up on the cross-connect wire, soldered to the relay contacts.
This is used by a number of engineers at remote transmitter sites. The C (common) and NC (normally closed) contacts from the relay are connected to the tip and ring of the transmitter site telephone line. When there is AC power, the relay is energized and presents an open circuit to the phone line. When the AC power goes away, the relay de-energizes and presents a short to the phone line. When the transmitter telephone line is called, the caller gets a busy signal since the phone appears off-hook. Simple; but it’s important troubleshooting information.
This little device has saved engineers countless trips to the transmitter when a call to the power company may be all that’s necessary. Although it could be left hanging in a rack, it’s better engineering practice to house the relay in a box, fuse the circuit and perhaps add a 620-ohm resistor in series with the relay contacts.
As one reader stated, the device we pictured certainly could be used to “surprise” an unsuspecting engineer who stuck his hand in the rack. (But then that never happens.)
Another wrote: “It’s always interesting to revisit a simple but very helpful idea from the past.”
Thanks to those who took the time to comment. Got a photo of a clever or puzzling gizmo? Send it along.
John Bisset has worked as a chief engineer and contract engineer for 40 years He recently joined Nautel as regional sales manager for Europe and Southern Africa. In 2007 he received the SBE’s Educator of the Year Award. Reach him at email@example.com. Faxed submissions can be sent to (603) 472-4944.
Submissions for this column are encouraged and qualify for SBE recertification credit.