(click thumbnail)Can you come up with a caption for this picture?Can you come up with a caption for Fig. 1? Email it to me at [email protected]. We’ll print the most creative captions in a future column.
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Kevin Larke is the chief engineer for the Mid Michigan Radio Group; like many engineers he does a little contract work on the side.
While he was installing an automation system at one of his contract station sites, the manager asked Kevin to check out the VHF Marti RPT-2 that a church uses every week for a one-hour broadcast. The staff said it sounded bad.
Kevin hadn’t planned this work, so he didn’t have his dummy load, frequency counter and related test equipment along. All he had with him was a Bearcat handheld scanner with unlimited coverage from 26 to 1300 MHz. Checking out the signal on the scanner, Kevin discovered that the Marti sounded best around 161.6475 MHz. It was licensed to 161.67 MHz.
In the past, Kevin has fed a tone into the Marti transmitter and set the center frequency by tuning for lowest total harmonic distortion on a distortion analyzer. Since he didn’t have a tone generator or distortion meter with him,
(click thumbnail)It’s an iPod. It’s a tone generator. It’s your backup audio source.an alternative plan emerged.
Kevin had brought his little Sandisk Sansa 512 MB MP3 player in his truck. He mainly uses it to listen to talk show podcasts while traveling. The MP3 player is patched into his JVC KD-HDR1 receiver. Yes, it’s HD, but as many buyers found out, it doesn’t decode RDS! The patch cable has 3.5 mm stereo plugs at both ends.
Kevin used Cool Edit Pro (now Adobe Audition) to create a minute of 700 Hz sine wave. He saved it as an MP3 and loaded it into the Sansa player via the USB port. He was able to use the same 3.5 mm stereo cable to patch it into the Marti RPT-2 line level aux input.
Then with the tone playing through the transmitter and received through the scanner, Kevin tuned the Marti frequency for minimum distortion. It’s easy to get the center frequency, just tune for the purest sounding tone. If the tuning is off a little, you can actually hear the harmonic distortion. Granted, it’s not precise, but better than it was before the adjustment. Kevin then ordered a new pair of crystals because the tuning slugs were at their limits.
Kevin saw a 256 MB MP3 player on clearance in a K-Mart for $20. His Sansa m230 512 MB player was only $35 at Best Buy. In a pinch, you could borrow an MP3 player from a teen!
(click thumbnail)Controls are on one end, the stereo jack on the other. Test gear in your teenager’s pocket.You could load a lot of high-quality test tones, white noise, etc. into one of these tiny players, making it a dirt-cheap little tone and noise generator to keep in the toolbox. It gives a pretty decent line-level output since it’s designed to drive 32 ohm ear buds.
That’s amazing technology considering the device only uses one AAA cell. Kevin adds that it wouldn’t be hard to add a resistive attenuator to drop the signal down to mic level.
Other simple mods could include the addition of a tiny transformer, switch and resistors in a box to get balanced line or mic levels. You could even get fancy and add various connectors and alligator clips. Of course there would be plenty of room left in the player for music and voice test audio files, too.
There’s yet another benefit. Once your tones are stored in the Flash memory, they stay, even if the battery is removed or goes dead.
Pretty cool, huh? A tiny pocket size test tone, white noise, pink noise, music and voice audio source for under $50. Such a deal!
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Dave Doherty manages the engineering for WBRU(FM), Brown Broadcasting in Providence, R.I. He got a slick Christmas present last year, seen in Fig. 2, an MP3 player like the one Kevin described above.
Fig. 3 shows the control buttons. The stereo mini jack is located on the opposite end of the player. Note the squeeze clip. It could fit on your lapel — or clip to a blank rack panel!
Dave’s application is to provide backup programming should there be an automation or STL failure at the station. Remember the adage “Good things come in small packages”? This one could really save the day as a backup for the station.
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John Pecore of Stormin Protection Products, manufacturer of the Optilator, writes that if your unit has been installed for more than four years, you ought to consider sending it back to have the batteries replaced and the unit calibrated.
For those not familiar with the Optilator: This device serves to isolate and protect equipment from telco surges using a fiber optic transmitter/receiver.
If your Optilator went dead for whatever reason and was replaced with a new one, there is a 90 percent chance that the factory can repair the dead unit. Repairs are $62.95 + $9.40 shipping, and they do accept major credit cards. John Pecore can be reached at (888) 471-1038 or at www.storminprotection.com.
The factory does not recommend that repairs or calibration be done in the field.