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Engineering Extra
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The Reference Room
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Workbench
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| Looking for Leaks? Try Formula 409 |
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by John Bisset,
8.02.2006
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John Bisset has worked as a chief engineer and contract engineer for four decades. He is the northeast regional sales manager for Broadcast Electronics and in 2007 received the SBE’s Educator of the Year Award. Reach him at (571) 217-9386 or jbisset@bdcast.com. 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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Fig. 1: Keep a spare blower motor on hand for that inevitable failure.
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Fig. 2: Don't launch a missile. Keep nitrogen tanks secured.
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Fig. 3: Mark the location of AM coil clips with a permanent marker.
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Yes, antennas and line sometimes will leak air. But if you're losing tanks of air on your pressurized FM lines, more than likely you will find the problem on the ground.
Armed with a fresh tank of air, pressurize the line to about 3 psi, as read on your regulator. Then spritz a bottle of Formula 409 or similar brand cleaner on the manifold, fittings and regulator assembly and along the hose connecting them. A multitude of little bubbles will point to your leak if it's on the ground.
You may be able to fix it, using a procedure contributed by Paul Sagi of Kuala Lumpur.
Paul recently traced a slow leak to a valve. It turned out the leak was a slow seepage around the valve stem, caused by the packing not sealing properly. Since he didn't have any graphited asbestos valve packing, and would not want to use it anyway, perhaps being overly cautious because of the asbestos, he took a length of Teflon pipe thread sealing tape.
Paul rolled the tape to make a thread, then doubled it and rolled it again. His goal was to obtain the length and thickness needed for the cavity under the packing nut. The fix works fine, and since the valve is not turned very often, it's lasted a reasonable time.
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B. J. Crabb from WFTA(FM) in Tupelo, Miss., wrote about the exhaust fan shown in the June 21 Workbench. Where do you find one?
A good place to start is the Grainger catalog. If you don't have it handy, go online to www.grainger.com and select "HVAC>fans" - you'll find 37 different fan categories. The site has a PDF catalog that you can download, but stock a ream of paper if you're going to print it out. You're better off contacting them for your own copy.
Grainger also has in stock the big blower motors used in high-power transmitters, as shown in Fig. 1. Even if you don't have the budget for a spare, note the model number and cost. This info can be a lifesaver should you lose your transmitter blower.
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If your nitrogen tanks aren't secured as seen in Fig. 2, you're playing with fire - or missiles.
A fire marshal once told me about a tank that fell to the floor, breaking off the regulator; the pressurized tank turned into a projectile, blasting through two cinder block walls and ending up in a field outside the transmitter building.
Don't take a chance. Keep caps on unused tanks, and secure those in use. Thanks to Paul Shulins at Greater Media Boston for sharing the tank securing methods.
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Have you poked around your AM coupling network or phasor lately? With the parameters all within tolerance, now's a good time to mark the location of all coil taps.
As seen in Fig. 3, a Sharpie brand indelible marker is used to mark either side of the clip. This must be done when you're off the air. The result, however, is insurance should a coil clip drop off or burn. You'll save hours of time resetting the coil to the marked location. Thanks to Grady Moates at Loud and Clean for sharing this useful tip.
If you like stories about building stations from the ground up, visit www.loudandclean.com for a reprint of an RW article by Grady about building an FM in Bermuda. It's great reading.
Ira Wilner of Wilner Associates, a broadcast engineering and technical services firm, writes that the current production run of Boston Acoustics Recepter HD Radios do not function as described by Cris Alexander in our June column. As this product is evolving, there will probably be more changes in the future.
Here's the latest update from Ira.
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1. Locking a station into analog:
a. Tune to the desired station.
b. Press the "alarm 1" and "alarm 2" buttons simultaneously and release.
c. This will put HD station into analog and keep it there.
d. To return to the HD mode, tune away from the station and then return to the desired station.
2. To get to the technical menu:
a. Tune to the desired station.
b. Hold down the "clock" button for 15-20 seconds.
c. You will get a master display with the following selections:
i. Version
ii. Hardware
iii. Audio Process
iv. Tuner ROM Writer
v. Split Mode
vi. Load Default Value
d. Pressing the clock button will exit this top menu.
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3. Scrolling through the menu
a. Left knob scrolls up and down.
b. Pressing the left knob takes you to the submenu or makes a selection.
c. Pressing the "display" button goes back to the previous menu.
d. Pressing the clock button will exit from the top technical menu.
4. Split mode
When you enter the split mode the radio will play at full volume.
5. Workaround for (4) above.
Use the headphone jack. You cannot adjust the volume with the front-panel knob on either the speakers or headphones when in the "split mode."
6. Additional headphone weirdness:
a. Sometimes, when you plug in the headphones the speakers will not mute. If this happens you can put the receiver into the standby mode with the on/off switch, plug in the headphones, then turn the receiver on.
b. The same thing happens occasionally when you unplug the headphones. The speakers will not unmute. So if that happens, put the receiver in standby with the on/off switch, then pull the headphones and turn the receiver on.
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Reach Ira via his web site at www.wilnerassociates.com |
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