Regular readers of this column will remember last year that Bruce Blanchard, engineering manager for the Salisbury University stations, solicited ideas to keep a nest of ospreys from using the dipoles of his STL dishes as dinner tables. He was losing his digital links to the transmitter sites. Readers provided a number of great suggestions.
Fig. 1: As osprey watches as plastic Spike Strips are installed on STL dishes. The latest update on the osprey problem is that the plastic spikes from Bird-X that Jack Elmore wrote about did the trick. Bruce bought them and had Terry Dalton and his crew from Stellar Communications Systems, based in Delaware, install them. The ospreys have not landed on the feed horns since.
Fig. 1 shows the installation in progress, with one of the birds circling. The ospreys did not like the crew on the tower at all, Bruce reports, but there were no incidents.
Bird-X supplies both metal and plastic spike strips, along with a variety of other items to deter birds or pests humanely. Bookmark www.bird-x.com. (Editor Paul McLane tells me he enjoyed reading on the website about some of the more imaginative solutions offered by the company for unwanted birds and pests, including a life-size alligator head, a "Terror Eyes" monster, a 3D coyote and "the World's First Indoor Laser Bird Repellent Device.")
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Here's a request and a tip, both from Chief Engineer Kevin Larke of the Mid Michigan Radio Group.
Kevin has two of the early 1990s Dolby DSTL still in service. They have been extremely reliable but one of his systems just starting having problems.
The forward and reverse power readings for the transmitter are stable, and the received signal strength reading on the receiver stays steady. But the bit error rate reading on the receiver jumps up intermittently, and the audio mutes for as long as 10 to 15 seconds.
Kevin and his staff took this pair out of service and switched to the backup Dolby system. That has been operating fine, so he can probably eliminate antenna problems or interference as the cause.
He called Broadcast Electronics, which had acquired the Dolby line sometime back, but he found that the line is no longer supported due to parts obsolescence. The technical manual has block diagrams but doesn't have detailed schematics or an alignment procedure.
Kevin asks Workbench readers if they have any suggestions or know of a reliable repair depot for these systems. It would be interesting to know how many are still in service, so let me know if you still have the DSTL.
And now, the tip:
More than a year ago, Kevin sent in a suggestion about using an MP3 player as a cheap and easy source of test tones and audio to keep in a toolbox. He also mentioned that white and pink noise can be saved on the player. Several readers reported that random noise couldn't be saved as an MP3 file.
Kevin didn't specify the file type when he sent in his tip, and he has three different Sansa-brand MP3 players that are all capable of playing MP3s, WMAs and uncompressed CD-quality WAV files.
Kevin can generate white noise and pink noise using Adobe Audition, then save the files to his players as uncompressed 44.1k WAVs. A one-minute mono file only takes 5 MB of memory, so even the test tones can be saved as WAV files, without hogging memory.
What's nice about using the MP3 player is the player can be set to repeat, so a one-minute tone can play for as long as you need it. Uncompressed CD-quality 44.1k stereo music WAV files can also be played on the players.
Even a cheap 1 GB capacity player can hold plenty of audio for testing. Kevin likes to use the wideband pink noise when nulling analog telephone hybrids. He says he gets better results using pink noise instead of a single-frequency tone to achieve the deepest null possible.
Fig. 2: Who knows what evil the elements will have on this directional coupler, mounted outside? * * *
From our "You won't believe this" file: Fig. 2 is a great reminder to consider your FM transmitter's harmonic filter when planning an installation layout.
Today's designs usually incorporate the harmonic filter inside the transmitter, so its placement is not a worry. But what do you do when the transmitter room is too small to house the transmitter and its harmonic filter?
In the case of Fig. 2, you stick the end of the filter out of the building. But then there's a directional coupler that needs to be connected. In this case, the coupler is outside with no protection; it's been this way for a long time. A roof extension would be nice!
Exposure to the elements is just another example of the resiliency of broadcast equipment, I guess.
Fig. 3: Connections Film and Video used six camera angles to capture the demolition of a LORAN tower in Alaska. Do you have a photo for our "You won't believe this" file? Your confidentiality is assured.
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Here's a sad but fascinating set of videos, produced in HD by Connections Film and Video. The company used six camera angles to capture the demolition of the LORAN station in Port Clarence, Alaska. The demolition took place at the end of April; Connections Film and Video shared the footage on YouTube. Simply search for "Port Clarence LORAN demolition." Thanks to the many engineers who brought this video to our readers' attention. Radio World contributor Frank McCoy adds that the video is a good demonstration of the manner in which guyed towers fall.
John Bisset marked his 40th year in radio in broadcasting recently. He is international sales manager for Europe and Southern Africa for Nautel and a past recipient of the SBE's Educator of the Year Award. Reach him firstname.lastname@example.org. Faxed submissions can be sent to (603) 472-4944.
Submissions for this column are encouraged and qualify for SBE recertification credit.