Put Stimulated Emission to Work for You

Turn On the Laser and You Have a Quick Way to Check the Axis on Your Satellite Connection
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Fig. 1 Mount a waterproof laser pointer to your satellite dish to verify alignment. Len Watson of Chicago's Scope+Focus Consultants offers a suggestion that should minimize downtime for your satellite connections.

The next time you get a call in the middle of the night that a storm blew through and the satellite is down, you'll start packing gear and be thinking signal chain. The first question that will pop up is look angle. You'll wish you had a quick way to know if the dish has been blown off-axis.

Anticipate this need. Spend 30 bucks now for a waterproof laser pointer and a couple of ground clamps or conduit supports. With the dish aligned properly, mount the laser to a part of the dish that would move if its aim changed — in Fig. 1, on one of the feed horn supports. Then point it to a "driveway" reflector, as seen in Fig. 2. Turn on the laser and you have a quick way to check the axis anytime.

Len suggests you mount the reflector 60 feet away. At this distance, the laser will move about one foot per degree off-axis.

Len provides two sources for waterproof laser pointers. Go to www.leisurepro.com and enter product code AQUULP in the Search field. Or try www.roithner-laser.com/Pointer.htm and scroll down to the underwater pointers.

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Fig. 2: A driveway reflector, mounted 60 feet away, completes the alignment setup. * * *

WA1MIK, Bob Meister noted a comment about a missing tower identification in the picture in the Nov. 19 Workbench (Fig. 3).

Bob adds a clarification for readers. Even though there is no tower identification sign visible by the tower, it's certainly legal to post such a sign at the entrance to the tower site. Two signs (one at the tower and one at the property entrance) are not necessary.

"Let's be fair," he writes. "How many tower ID signs do we really need at a site?"

Great point. In fact, I'd say the sites I've visited are divided 50/50 between signage on the tower and at the entrance. The advantage to having signage at the entrance to the property is that information can be copied easily from the road; site entry is not necessary.

Do you need a source of tower site signage? Try Antenna ID Products in Glenmoore, Pa., at www.antennaid.com. Another is Curt Bennett's Sign Pro of Lexington, Neb., co-owned with KRVN(AM). Call (888) 230-7446.

Let them know you heard about them from Radio World.

One thing that grabbed Bob Meister's attention in the photo was the lack of ground wires on the coax feed line or any other cable entering the building. These lines should be grounded outside the building, close to the entry point, as well as the base of the tower — basically anywhere they change direction by 45 degrees or more.

Lightning will continue to follow a straight path; you want it to go down the ground wire rather than into the building, where it can do more serious damage. Of course, ground connections inside the building won't hurt either.

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Fig 3: Make sure lines entering the transmitter building are grounded properly. Although we can't see the incoming electrical service, it bears inspection, too. Who knows what evil lurks around that entry point? Ditto with the incoming telephone lines.

Is there water and sewer service to the building? What about outdoor lighting, especially over the entry door? Is there a backup generator? What's the condition of the generator enclosure? Fuel source? Fuel tanks? Fuel line? Any nearby satellite dishes? STL antennas on the tower? GPS receiver antenna for the HD Radio exciter? Any windows in the building? Are they barred securely?

The list can go on and on.

* * *

On a different subject, awhile back we had a discussion of running uninterruptible power supplies with backup generators and how some couldn't cope with the "less-than-perfect" power.

An AM station where Bob Meister works has that problem. They're using a TrippLite online UPS — an inverter runs the load 100 percent of the time — and they have an old Onan mechanically-governed generator at the transmitter site. The UPS refuses to accept the incoming AC power when on the generator, so it runs exclusively on its batteries, not even trying to charge them.

Since this is an AM station, the load on the generator naturally varies with the audio content. It's impossible to guarantee 60.0 Hz operating frequency. After running half an hour, the UPS has no choice but to bypass itself and revert to the incoming AC power, no matter how good or bad it is. Of course all the equipment continues to function fine.

When the commercial power comes back, the generator shuts off, but the UPS with dead batteries can't do anything about that momentary outage, so all the powered loads lose power for a few seconds. Not good for equipment running Linux, such as HD Radio exciters.

Bob contacted TrippLite, which told him there's nothing it can do to its units to allow them to accept "less than computer-perfect power; that's what their units expect and require," as he quoted the conversation.

If you're going to have perfect power all the time, who needs a UPS? This is the real world. Power fails.

Bob investigated the market and found that Liebert makes a similar online UPS (GXT2 series) that accepts AC power from 40 to 70 Hz and claims to be compatible with standby generators by not being so critical of incoming power. After all, it's just charging the batteries and keeping the inverter running. It shouldn't care about the voltage or frequency of the incoming power; the inverter will clean it all up and feed the load anyway.

Bob bought one of the company's units but has yet to drag it down to the transmitter building and go through a power-fail situation to see how well it does. But at his house with a standby generator running at 60.5 Hz, the Liebert model works fine. It would seem that Liebert listened and designed a UPS that eliminates many of the problems people have with older generators. Not everyone can afford a computer-controlled genset that holds the output frequency at exactly 60.0 Hz.

From the Liebert Web site, www.liebert.com, one of the features is the unit's compatibility with backup generators. The unit boasts the ability to handle frequency variations and other power fluctuations that occur during generator operation.

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. He was SBE's Educator of the Year for 2006. Reach him atjohnbisset@verizon.net. Faxed submissions can be sent to (603) 472-4944.

Submissions for this column are encouraged and qualify for SBE recertification credit.


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