Contributor Dan Slentz passes along a relevant question from Doug Nelson: What kind of fire extinguisher should you install at your transmitter site?

There are six common types, according to manufacturer Kidde:

• Dry chemical agent extinguishers form a crust to remove oxygen and keep it from spreading. 
• Water types absorb the heat, cool the burning material and remove oxygen. 
• Wet chemical types seal the fuel to prevent vapors from igniting and cool the fire. 
• Carbon dioxide types remove the oxygen and replace it with pressurized CO2 gas.
• Halotron is a clean agent fire extinguisher that discharges a non-conductive rapidly evaporating liquid. 
• And foam types smother the fire by creating a barrier or film of foam.

According to the National Fire Protection Association, extinguishers carry a letter rating that corresponds to the type of fire a device can put out:

• Class A are fires in ordinary combustible materials, such as wood, cloth, paper, rubber, and many plastics. 
• Class B are fires in flammable liquids, combustible liquids, petroleum greases, tars, oils, oil-based paints, solvents, lacquers, alcohols and flammable gases.
• Class C fires involve energized electrical equipment.
• Class D are fires in combustible metals such as magnesium, titanium, zirconium, sodium, lithium and potassium. 
• And Class K are fires in cooking appliances that involve combustible cooking media like vegetable or animal oils and fats.

With all the equipment at a transmitter site, you certainly don’t want to use an extinguisher that will leave a residue that can ruin the electronics. To avoid damage, steer clear of Class A and B dry chemical extinguishers. 

Engineer Blaine Wilson writes that Halotron, made by American Pacific, is a brand of “eco-friendly” halocarbon fire extinguishers that are non-conductive and leave no residue, suitable for Class A, B and C fires. 

You should also consider an extinguisher’s rating and weight. The sites mentioned above have information to guide you.

What’s your experience? And have you ever had to use an extinguisher at your site? Email me.  

Engineer Steve Michaels suggests you take this question to your local fire department.

This seems a good idea on several fronts. First, you will get the latest information. Second, many departments will offer a free fire inspection of the transmitter site. Third, it’s a nice excuse to build a relationship with your local emergency responders.

Tube rebuilding

With Microwave Power Products closing the former Econco facility, engineers will be looking for an alternative source for tube rebuilding. 

Steve Tuzeneu writes that Massachusetts-based Kennetron rebuilds vacuum tubes, oscillator tubes, power grid tubes and electron valves used in broadcast and industrial applications. Do you have experience with the company to share? 

Frank fixes a leak

Consultants Frank and Dave Hertel share a simple fix to a problem that you might encounter. It’s an emergency end cap for a 1-5/8-inch transmission line.

Perhaps you are on a job and the station’s “staff IT engineer” has an old transmission line adapter on a line that is leaking air excessively. His nitrogen tank is going “empty” once a day. 

The nitrogen tank feed for the 1-5/8-inch line unfortunately is in parallel with a 3-1/8-inch line. The leak occurred when the engineer removed the 1 kW FM transmitter in order to send it to the factory for repair.

Since he didn’t have a spare transmitter, he and management understood they would be off the air for some time. Fortunately, they also realized that their high-power transmitter should be protected by having nitrogen on its 3-1/8 line. The nitrogen feed is simultaneously on both the 3-1/8 and the 1-5/8 line so it would not take on any moisture.

Lady Luck must have been with them because a previous RF engineer had left a stockpile of parts and pieces. They found an old cut-off EIA 1-5/8 flange and converted it into an end cap. The flange caps the bottom run of the EIA flanged 1-5/8 coax while keeping pressure on both coax lines.

The photos show you how to correct the station’s line pressure requirement while awaiting a new, non-leaking adapter/connector for the 1-5/8-inch line and the return of the transmitter.

This can be used outside, if need be. It will withstand winter and summer conditions. The plug for the coax end is a 1-1/2-inch expandable freeze plug, also known as a welch plug, available from Amazon or an auto parts store.

Workbench submissions are encouraged and qualify for SBE re certification credit. Email johnpbisset@gmail.com.

[Read Another Workbench by John Bisset]

 

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A longtime consulting engineer who now works for the federal government saw our discussion of mnemonics for remembering the resistor color code. He shares one he learned in college. It goes “Budweiser Beer Rots Our Young Gut, But Vodka Goes Well.” Hey, whatever works!

Barcode lookup

I was chatting with some colleagues recently and we all agreed that the smartphone may well be the best invention for engineers of modern times. These apps do pretty much everything.

Paul Sagi just told me about an app called Barcode Lookup that turns your phone into a barcode scanner. It contains 1.6 billion codes.

Let’s say you spot a product at the hardware store but want to know more about it or compare prices from other sources. Open this app on your phone to scan or plug in the UPC number. You will see descriptions, images, online stores, reviews and other useful information. You can also store the results.

The platform contains five barcode types known as Global Trade Item Numbers. They include UPC, EAN, ISBN, JAN and ITF-14.

The app is available on the Apple and Google app stores. Learn more about this simple but fascinating tool.

Broadcast manuals

How about a stroll down memory lane? Frank Hertel, principal engineer with Hertel Engineering, told us about a great page that has many old equipment manuals and catalogs.

The page is part of the invaluable WorldRadioHistory site run by David Gleason. It’s under Technical & Electronics, listed as “Catalogs of Equipment Manufacturers.”

It’s fun to peruse, say, a catalog of equipment from Bradley Broadcast from the 1990s (several of which were edited and co-designed by our editor Paul McLane in a previous job), or to read a manual for AEL transmitters, or look over documentation about a Tapecaster cart machine.

Do you miss names like McMartin, Allied Broadcast, PR&E or Schaefer? Get ready to go down the rabbit hole.

Priceless data sheet

We’ve mentioned in the past that the audio performance of old Western Electric transformers, many of which were used for equalized remote service, makes them a keeper.

San Francisco projects engineer Bill Weeks shares a data sheet from 1958. It identifies the transformer type (first column) and the operating specs in subsequent columns.

This is too small to read here, so we’ve posted it and you can download it as a PDF.

Archie’s site tips

In a recent Workbench, Dale Lamm shared a list of things to do before leaving a transmitter site, the kind of reminders you might want to post by the door.

We asked for more ideas. Archie Simpson responded with these:

• Are AM ATUs at each tower base closed and locked?
• Are the tower fences closed and locked?
• Is the generator fenced in and locked?
• Is the satellite dish fenced in and locked?
• Have the computer monitors been turned off?
• Have all non-security lights been shut off?

And finally, one that can easily forgotten easily at 3:20 a.m.: Is the alarm turned on and the remote control not left in “local” mode?

Air conditioning caution

With warmer weather coming for most of our readers, Florida-based engineer Don Browne reminds us also to keep an eye on the air conditioning at the transmitter site.

Check the air outlet and intake, and determine the difference in temperatures. Depending on outside conditions, the difference should be around 15 to 20 degrees F.

Air conditioning systems generally can be expected to only cool to about 20 degrees below the outside air temperature. But if the system isn’t cooling efficiently, act before you have a problem.

Lights, camera … no, LIGHTS!

My former Telos colleague Kirk Harnack has joined the technical staff of Josh Bohn’s company MaxxKonnect.

Kirk also is a broadcaster and installed color WiFi cameras at his transmitter sites. He intentionally leaves on the LED overhead lights for best visibility. But sometimes people turn a light switch off, impairing the use of the cameras.

To prevent that, he installs cable clamps. When someone really wants to turn the switch off they can do it with a screwdriver.

Kirk is always ready with a good tip. He learned this one from broadcast engineer Ray Vaughn.

Workbench submissions are encouraged and qualify for SBE recertification credit. Email johnpbisset@gmail.com.

[Read Another Workbench by John Bisset]

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Ben Dawson, P.E., principal engineer of Hatfield & Dawson, wrote to tell us about KNUV, an AM station licensed to Tolleson, Ariz., a suburb of Phoenix. The station was required to vacate its longstanding transmitter site. 

This is not an unusual situation for an AM station to find itself in these days, given the trends in urban development, the ever-rising value of real estate and the business challenges facing all AM stations.

With advice from Ben’s firm, the licensee and her technical contractor conducted a thorough search and decided to relocate to the site from which Phoenix station KXEG(AM) broadcasts. 

KNUV now broadcasts on 1190 kHz with 640 watts day, 22 watts night. KXEG is on 1280 kHz with 2.5 kW day, 49 watts night. The KXEG site has an equipment building that had more than adequate space for KNUV’s equipment.

The single 180-foot KXEG tower is close to the building, so they chose to install the diplexing filters and antenna tuning unit matching networks in an equipment room, and the tower is fed through a bowl insulator in the building wall via a well-supported copper tube to the tower base.

The filters and match networks for multiple frequency use of an antenna require segregated enclosures to electrically isolate the individual networks from one another. 

A three-cabinet phasor, formerly used at KXEG’s three-tower directional site, was chosen to house the antenna equipment. One cabinet was used for each frequency’s filters, and the remaining cabinet was separated with a shelf into an upper and lower compartment, one for each of the ATU matching networks.

Fig. 1 shows a view of the cabinets before stripping components.

Thomas Driggers measured the antenna impedances at both frequencies, and Steve Lockwood prepared a design for the system networks. Network values were selected to provide reasonable sideband loads to the transmitters of the two stations, using various software tools and with attention to the dictates of Ron Rackley’s “VARs matching” technique (described by Rackley in the 11th edition of the NAB Engineering Handbook, Chapter 7).

Once the design was in final draft form, the component list was prepared, and the team created an inventory. Components from the former phasor and ATUs were used where appropriate, and parts from available surplus collections were gathered to complete the inventory. 

The phasor itself and the two ATUs were removed from service at the original KNUV site, with one left for STA operation. 

The final system was constructed by Driggers entirely of surplus material and components except for a few feet of new 4-inch copper strap. Fig. 2 shows some of the surplus parts used. 

The surplus items were inspected and measured carefully. Because filters often require high-voltage capacitors and high-inductance coils, the team found it necessary in at least one case to obtain the necessary inductance by using two available coils in series, shown in Fig. 3. 

The vacuum capacitors that were to be connected in series parallel to obtain the necessary voltage-handling capability in the filters were evaluated with a hi-pot tester.

Given the cost of replacement “new” parts, the package of additional components was packed up with care and insured for shipment to Phoenix. 

When all parts were on site, the phasor cabinet was stripped and a shelf installed in the cabinet for the ATU networks. Parts were installed to minimize interaction. In particular the KNUV 1190 pass 1280 reject filters were connected to the KNUV ATU cabinet with a coaxial cable to avoid any coupling to the 1280 pass 1190 reject filters in the center cabinet. 

(You can read a paper by Ben Dawson, “Isolation Requirements in Diplexed MF Antenna Systems.” At Hatfield & Dawson’s website, scroll down to “isolation requirements.”)

Fig. 4 shows this coaxial cable from filter cabinet to ATU cabinet on the right side.

Though the resulting system is far from physically elegant, it is electrically straightforward and performs well. Fig. 5 is a rear view of the completed system.

The trends I mentioned at the beginning have driven a virtual explosion of diplexed, triplexed and even quadriplexed installations, some at sites with as many as nine existing towers.

Under these circumstances, the project cost for multiple use of existing antennas requires careful consideration. In some cases simple systems can be implemented with lowest cost by “hand-made” or “composite” systems, if qualified design and construction personnel are available.

Ben adds that in his teenage years, half of the local AM stations had handmade transmitters, and many had handmade audio console equipment. “Not something often seen in modern installations,” he said.

Workbench submissions are encouraged and qualify for SBE recertification credit. Email johnpbisset@gmail.com.

[Read Another Workbench by John Bisset]

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