In the Feb. 2 Workbench we showed pictures of wiring conduit used by Tony Gervasi and Dirk Nadon of Nassau Broadcasting. Needing a means to route wires into and out of their equipment racks in the technical center, they chose large diameter PVC pipes, painted black to match the racks and connected to the top of each rack.
Frank McLemore runs a contract engineering business that serves as the market engineer for the Clear Channel cluster in Columbus, Ga. There are three AMs and five FMs in the group. Frank performed contract engineering for most of these stations going back to when they were owned separately by individual companies. The stations were consolidated into an eight-station group by Cumulus in 1999 and sold to Clear Channel the next year.
Frank agrees with Nassau's use of PVC pipes to clean up cables leaving an equipment rack. During the studio consolidation for Cumulus, similar pipes were installed. As seen in Fig. 1, the PVC pipes also support a wire trough.
(click thumbnail)Fig. 1: PVC pipe serves as a conduit
Looking for a cheap source for wire racks? Try the shelving and closet organizer section of a hardware store. The white vinyl-covered wire shelving is inexpensive, looks nice and keeps the wires organized as you can see in Fig. 2.
(click thumbnail)Fig. 2: Close organizer shelving makes an inexpensive wire trough.
At the Columbus site, Frank has two rack rooms joined by the wire rack trough through a hole in the wall. He suggests that if you need to bend the shelving, take it to a sheet metal shop for a good straight bend.
McLemore can be reached at firstname.lastname@example.org .
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The breadth of knowledge and experience possessed by Workbench readers amazes me. It also makes this column great fun to compose.
You'll recall that Mark Goff of Eagle Communications had questions about E. F. Johnson components used in a very old phasor belonging to a station his group had acquired (Feb. 16).
What better resource to answer his questions than a former employee of E. F. Johnson? Veteran engineer Jim Stanley, W6GH, is now with Infinity's KOOL(FM) in Phoenix. Jim writes that he worked at E.F. Johnson in Waseca, Minn., as manager for the engineering department during the mid to late 1990s. In 1997, the company was sold to Transcrypt International in Lincol, Neb.
To Jim's knowledge, there were prints, procurement documents and drawings stored in the print room in Waseca. As a number of years have passed, he's not sure if the material Mark needs is still there. But it's Jim's guess that the information is still available in some form. The challenge will be finding the right person to help you. Jim writes that the company is barely a shadow of its former self.
Jim suggests calling the main number in Waseca and inquiring as to who is in charge of the print room and documentation. Mark will need the EFJ part number, which should be embossed on the inductor in question.
The main number at E.F. Johnson is (507) 835-6222. Thanks, Jim for providing this resource. If you maintain an older AM, with E. F. Johnson components, keep this number handy.
Jim Stanley can be reached at email@example.com.
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Like Jim, Mark Humphrey, the engineering manager at Radio One in Philadelphia, has been around the engineering block a few times. Mark is well versed in a variety of broadcast engineering issues, and especially RPU matters.
Mark replied to Dick McGraw of McGraw-Elliott Media Group. In our Feb. 16 column, Dick was looking for a portable FM receiver that was immune to Marti/RPU 161MHz interference. Mark's suggestion is to try a notch filter, or trap, ahead of the FM receiver to reduce the interference. He has had good results with the 5KV "FasTrap" product, made by Microwave Filter Co. in East Syracuse, NY.
Visit these two Web sites and bookmark them: www.microwavefilter.com/tubularbody.htm and also www.microwavefilter.com/negativetraps.htm
These traps are inexpensive and normally are sold to cable TV operators to delete pay channels from non-subscribers. However MFC can supply them for any frequency in the VHF range. Just specify your Marti frequency when you order. The price is around $25 per filter. Mark has also used these filters in the 2 meter ham band.
The filter should attenuate the Marti interference by at least 30dB. Install the trap directly on the antenna input terminals of your FM receiver. Mark suggests finding a portable receiver with a metal case, and an "F" connector for the antenna input for best results.
At Mark's WPLY they use an older Dayton Industrial FM/SCA tuner in the remote truck, and the FM receive antenna (a homebrew folded dipole inside PVC tubing) is mounted atop the mast, just 30 inches above the Marti's transmit yagi. Mark says they typically run 40 watts on 161.67 MHz.
With the trap in line, there has been no overload problem. In fact, even the SCA (which is used for IFB from the studio) is clean.
Mark Humphrey can be reached at firstname.lastname@example.org.
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Dr. K. Dean Stephens is a Senior Broadcast Engineer. He notes that we've probably been blitzed with suggestions for handling dirty power from a generator feeding an unhappy UPS (and we have; watch for a future column).
Dean offers one of the simplest solutions. The problem is solved by charging the UPS system from the generator. Don't switch critical equipment to the generator power, just wire the generator output to a DC charger, which will feed and charge the UPS batteries. The equipment will run off the UPS, but the charger will keep the batteries happy.
Thanks, Dean! Reach Dr. Stephens at email@example.com.
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