Back when radio stations still had DJs, one would occasionally get the frantic “We off the air” call:
Nowadays, the unemotional monotone computer-generated remote control voice says something like “Alarm, status channel 16, WXYZ silence…” or better still, the answering service.
In some ways, I miss the old days…
Today, there will be a quiz.
Recently, we had an AM antenna array go out of tolerance by a good margin. This has been repaired, however, I thought I’d post this information and see if anybody could identify the problem and the solution. Unfortunately, I don’t have prizes to give away, however, you can show off your AM engineering prowess.
All of the information is pertinent:
Readings:
| Tower | Phase angle as licensed | Current ratio as licensed | Phase angle as read | Current ratio as read |
| 1 | 147.2 | 0.583 | 149.5 | 0.396 |
| 2 (reference) | 0 | 1.00 | 0 | 1.00 |
| 3 | -137 | 0.493 | -125.8 | 0.798 |
| 4 | 107.5 | 0.481 | 92.7 | 0.355 |
| 5 | -38.1 | 0.737 | -60.2 | 0.623 |
| 6 | -178.7 | 0.382 | 142.8 | 0.305 |
Licensed values for common point current is 13 amps, impedance is 50 ohms j0 and there is normally no reflected power on the transmitter. On this day, the common point current readings were 8.9 amps, impedance 38.5 ohms +j5 the transmitter had 340 watts of reflected power.
This is the overall schematic of the phasor and ATU:
Aerial view of the transmitter site, oriented north:
So, where would you begin? Ask questions in the comments section.
During the digital TV conversion in the US, all broadcast television stations installed new transmitting equipment and antennas. Most stations ended up on a different frequency than their original analog channel. In Albany, New York, all of the TV stations moved to a common transmitter site and installed their antennas on a single tower.
For more on the Albany DTV site, check out the NECRAT page: www.necrat.us/albdtv.html
So, what happened to the old Analog TV sites in Albany?
For the most part, after the analog turn-off on June 12, 2009, the sites have sat empty. Such is the case with the former WMHT site.
This old sign about sums up the end of analog television.
The former transmitter operator desk. The maintenance log is still open. From the looks of things, they opened the circuit breakers and walked away. Everything remains intact from the antenna to the klystrons and exciters. It does appear that the coolant has been drained from the system. Other than that, it seems like the whole thing could be restarted with minimal effort.
There were two Onan DFN 350 backup generators. With a TV transmitter, running the cooling system after shutdown is vital. The idea here is that both generators in parallel could run the whole station, if one generator failed, then the cooling system would still run and cool the klystrons.
The former WMHT tower, which currently holds the WVCR-FM, WXL-34 (NOAA weather radio), and W44CT-D (Three Angles Broadcasting) Low power TV transmitter.
These equipment racks and the NOAA weather radio transmitter in the other room are the only active equipment at this site.
WMHT-TV Chanel 17 (488-494 MHz) was signed on 1962 from this site. The Comark transmitter was installed in 1984. The station’s analog ERP was 2000 KW visual, 200 KW aural.
It is an interesting site.
High winds seem to be the culprit in the collapse of two towers in North Adams. According to the Motorola system technicians, it happened at about 12:30 am Sunday morning, which is when all their link loss alarms started going off. The larger, self-supporting tower broke from its mounting plate and tipped over into the smaller guyed tower next to it. Effected are WUPE-FM and W226AW (WFCR New England Public Radio) as well as NEPR’s new station WNNI which has not officially signed on.
Cellular service for ATT, Verizon, and Sprint/NEXTEL were all knocked offline as well as internet services and E911 dispatch. Those services are coming back online, with temporary modular cell units en route. N
Here are some pictures:
For pictures of the towers during happier times, refer to this post: Filtering for co-located FM transmitters.
Restoration work is underway with WUPE-FM expected to return to the air at low power by Monday afternoon.
WUPE-FM was returned to air at low power by about 1pm on Monday 3/31. We took an unused Shively 6812 antenna that was tuned to 94.1 MHz and retuned it to 100.1 by cutting 1/4 inch pieces from the end of the elements until it was on frequency. It took a bit of doing, but with a network analyzer, we were able to get it to 1.2:1 SWR with symmetrical sidebands. Running 600 watts, it covers the city of license and then some.
The STL antenna is a survey antenna mounted on the side of the building. In this configuration, with the leaves off of the trees, we are getting about 250 uV signal, which is pretty good.
The site is now crawling with insurance investigators, cell site technicians, North Adams fire department, Berkshire County Sheriff’s officers, tower workers, etc. After we finished this work, we cleared out to make more room for everybody else. Estimated restore time for W266AW is Wednesday 4/2.
Planning for the replacement tower is already in progress, I’d expect it to happen fairly quickly. The next step for the broadcasters is to put up a 70-foot utility pole and get a full-powered antenna for WUPE. This should happen in the next two weeks or so. That will serve as the temporary facility until the new tower is constructed.
