A Simple Lock Check Pays Dividends

This is a good time to check site security locks before the really bad weather rolls in. Are the hasps bent? Are locks rusted? Do keys work? Better to learn these answers now than find out when you can't get into a site in an emergency.
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This is a good time to check site security locks before the really bad weather rolls in. Are the hasps bent? Are locks rusted? Do keys work? Better to learn these answers now than find out when you can't get into a site in an emergency.

This is a good time to check site security locks before the really bad weather rolls in. Are the hasps bent? Are locks rusted? Do keys work? Better to learn these answers now than find out when you can't get into a site in an emergency.

This is the kind of inspection an intern can make. Have him or her snap pictures of all locked gates and doors. Review the pictures with the intern and develop a plan of corrective action.

(click thumbnail)Fig. 1: The Trackstick II provides GPS tracking data and runs for a week on two AAA batteries.
If all hasps are secure, squirt some liquid graphite into the lock and work the mechanism with a key, locking and unlocking until the mechanism is thoroughly lubricated. You'll be thankful for this corrective action when you arrive that cold and icy morning.

* * *

With the football season in full swing, Radio Director Darren Morton of Grove City College in Pennsylvania decided to replace the station headsets and remote mixer.

The station's football remotes are done primarily on POTS lines, with the occasional venture into "hellular reliability" just to make things interesting. Darren liked the features on the new JK Audio Remote Mix4, especially the Bluetooth capability, so he bought one.

In the past, he's used the Sennheiser HMD24 headsets (with dynamic mics) and had great success. With the new RM4 offering phantom power, he opted for the AKG HSC271 headsets (with condenser mics).

When he first plugged this combination together, he could barely raise the input gain before it went into clipping. He expected the condenser mics to be somewhat hotter than the dynamics; but this much gain made it unusable. It's been Darren's experience that getting "talent" to set gains correctly in the field is akin to negotiating a hostage release!

Comparing the AKGs to the old Sennheisers on a different mixer revealed only a slight difference in relative output. So he put a tone generator set at –30 dB into the JK and confirmed that its mic preamps were indeed very hot.

A call to JK got him a set of schematics.

The input preamp on the JK is a great opamp, the Analog Devices AD8221. Some research on it revealed that its gain can be set by one resistor connected between pins #2 and #3 (Rg). JK uses a 499-ohm resistor for a gain of 100. Using some simple math and figuring a gain of about 25 gave him a 2k resistor value which would knock 12 dB off the input.

Inside the JK RM4, the gain resistors are marked as follows: ch#1- R4; ch#2-R13; ch#3-R21; and ch#4-R33. They are located in line with their corresponding inputs. The only problem is: those resistors are SMDs, surface mount devices, and darn-near microscopic.

So out came the reading glasses and the forceps for surgery. On the plus side, the printed circuit board is relatively hardy. The result was good, although Darren could have thrown away some more gain and still had plenty to spare. The AKG mic headset worked great.

Of course, his actions here probably invalidated the warranty. But Darren is confident in the surgery and adds that JK equipment has never let him down before.

The company's Joe Klinger adds: "We also hear from others who would like more gain. It's difficult to design one preamp circuit that will work equally well with all microphones and in all environments. The original design offers a respectable working range for most microphone/environment combinations."

(click thumbnail)Fig. 2: Make a visual inspection of transmitter site locks and hasps at least once a year.
* * *

Here's something fun, especially if you run AM radial measurements or monitor points.

The Trackstick II is a small GPS device that continuously records its own position for later download through a built-in USB connector. Plug it into your computer to see your exact route on Google Earth, Microsoft Live and many other online mapping programs. Recorded data includes date, time, location, speed, heading, altitude and the exact length and location of any stops.

The Trackstick II is popular among hikers, bikers and boaters but also among engineers who want to record an exact history of their travels for later review on digital maps. Wondering where the intern takes the remote vehicle after the remote? The Trackstick II tells all!

For monitor point location, the included software can embed location data into your photos to show the exact spot that your pictures were taken. Trackstick II is also compatible with Flickr, Myspace and other online communities that accept geotagged images.

The Trackstick II runs on two AAA batteries which can power the device for up to a week. Visit www.trackstick.com for information.

* * *

A safety tip is forwarded by Mike Langner of Albuquerque, N.M.; it also was reported by Radio World Newsbytes recently.

The U.S. Consumer Product Safety Commission and RadioShack issued a voluntary recall of two models of the retailer's DC power supplies. Users are warned to stop using the recalled products immediately. RadioShack notes that there are about 160,000 affected units in the recall.

RadioShack's part numbers are 22-507, a 3A supply with an automotive lighter jack and binding posts, and 22-508, a 15A supply with binding posts. Date codes of the affected units are from 08A04 through 01A08. The date code format is MMAYY where MM is the month and YY is the year. The catalog number and date code are on the back of the power supply. The supplies were sold at RadioShack stores from October 2004 through January 2008.

Power supplies with a green dot on the product and the product's packaging have been repaired and are not included in the recall. The recalled power supplies are wired incorrectly, posing electrocution and fire hazards, though no injuries had been reported.

Owners of recalled supplies can return them to any RadioShack store for a free repair. Registered owners of the recalled power supplies were to be mailed a notice. Additional information is available through RadioShack at 800-843-7422 or www.radioshack.com/recall.

Mike Langner is a former station owner, PD, GM, DOE and chief engineer. For the last four years, Mike has provided broadcast consulting services to a variety of clients, including the New Mexico Association of Broadcasters.

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Keep the Goodies Under Lock and Key

I recently spoke with an engineer who told me of nests of black snakes he found in a previously unused communications building. As snakes search for warmth, they are drawn to a transmitter building's heat source.

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A True Remote Transmitter Reset

Ed Bukont of Commstruction and Services remarked about our reminder to check filters and heat sinks on solid-state transmitters, often overlooked because the transmitters run so reliably.