Boston-area over-the-air TV outage - again

The nitrogen gas is in a conduit surrounding the transmission line to prevent the formation of moisture. Any kind of moisture could cause a serious problem such as a short circuit or electrical arc especially at the voltages and wattage they are dealing with. Sometimes such an arc is not visible but will show as a compromised output. It definitely shows up on the control panels below!

I've had to be in transmission facilities of this nature in the past. Consider this... at home you have a cable TV line that is coax cable and its about 1/4 inch in diameter (plus or minus) or about the width of your pinky finger. The coax line in these facilities are full solid copper pipe about the width of your upper arm (about 3-4 inch dia.). The center conductor is about as wide as your thumb. I simplify here.

The transmission tubes (yes they have a tube) is in a special housing with a peep hole for inspection purposes. The peep hole has a special tinted glass to cut down on the light and radiation it emits, and you have to wear special goggles if you should be unfortunate enough to have to look in, which is usually only allowed for a second or two.

Many of the transmitters are pooled together these days sharing a tower as a money-saver which is why this often takes down several stations at the same time. There used to be 3-4 such towers in Needham, and I think that still applies. WHDH (CH 7 & 56) is the free-standing tower off Needham St.

All of these stations have both main and auxiliary transmitters. When maintenance on the main transmitter is needed, usually on weekends and at night, the switch over is seamless between 12 midnight and 2 AM. That can last till between 5-6 AM Monday morning. Usually the aux transmitter is enough juice to get the signal out when there is less clutter in the radio spectrum at night on weekends, but some people can loose the stations or they will be hard to pull in under the new digital format. In the old analog days you pretty much never noticed it.

Speaking of gas insulators... For those who live close, or are near West Roxbury you probably have noticed an electrical distribution yard next to Roche Bros Market parking lot on Willow St. That yard has a high voltage line connecting it to the electrical yard on Hyde Park Ave around #750 in Hyde Park. It was laid in the early 1970s by United Technologies for the then-Boston Edison. That HV line has a special "oil" that surrounds the transmission line that was injected that helps insulate it and protect it and prevents the formation of moisture much the same way the gas does the job at the TV towers. This is a common practice where high voltage and power is found.

As for gas powered... yes most have a back-up generator but those may be powered by diesel or natural gas.

I chided GBH several times in the last few years asking them to post something when they were down for what ever reason and it seems between my complaints and those of others they took these steps to keep us informed. Sadly, they are the ONLY station that appears to be doing this with a blog page. Given that these outages can and do impact other broadcast frequencies, it is a good source to bookmark. If other stations are doing it, it's an afterthought since for many the broadcast medium (via antenna) has become secondary to their feeds going out via cable and satellite. Of course CVB's recent snit with Direct saw them touting the free antenna signal. Maybe they will rethink things now.