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Re: Lightning Taking Out AM-HD Signals

S

Savage

Re: Lightning Taking Out AM-HD Signals

Lightning can take out anything at an AM transmitter site. The safety of your gear depends on how well grounded everything is, and how well-engineered and maintained the lightning and static-discharge gear is.

All equipment racks should be brought to station ground (NOT utility) with 4" copper strap tied to the ground system, phasor and co-ax shields. Ball and horn gaps out at the towers should be correctly gapped and adjusted for minimum clearance without arcovers on modulation peaks. Static drains should be carefully checked at each tower (if your system doesn't have them, get them. Generally static discharges are far more troublesome than direct lightning hits.) One weak link here and computer stuff - which is essentially what an HD exciter is - is asking for big trouble.

HD Radio is very susceptible to any kind of impulse interference - lightning hits, atmospheric static discharges or contactors opening/closing causing sparks - and on and on. Anything that causes packets of digital data to get scrambled or lost - poof! You're listening to analog. (And frequently analog which is not time-aligned with the digital....)
 
Re: Lightning Taking Out AM-HD Signals

[EDIT-quote removed]
Click to expand...

Notice that the time it takes to re-acquire digital lock is much longer than the duration of the lightning strike. Is this a good tradeoff?

Imagine how this clip would sound if the station were full-digital without analog to fall back on (iBiquity's long-term goal.) But we don't have to wait forever to experience this problem. Current IBOC receivers have these muting problems when forced to digital while tuned to a station operating in "ballgame mode" with the analog delay defeated. I can't think of a better way to encourage tune-out.

Fortunately, the lightning problem is much less severe in the VHF band because static discharges generate less noise at higher frequencies. That's why we should be looking at the BMC proposal if we're serious about solving AM's biggest problems.
 
Re: Lightning Taking Out AM-HD Signals

[EDIT-quote removed]
Click to expand...

Sherry,

It doesn't have to happen all at once. Just like with the expanded AM band, it could be phased in over time. Many radios actually already tune 76-88 MHz, since those frequencies are used in Asian countries.
 
Re: Lightning Taking Out AM-HD Signals

Lightning is a BIG problem for digital TV, particularly on the low band (channels 2-6). When there is a lightning strike, the picture freezes and the sound cuts out, and it takes a LOT longer to recover than analog TV did.

Often this happens during severe storm alerts, when people really need to get the message.
 
Re: Lightning Taking Out AM-HD Signals

It doesn't work so hot on UHF, either Audioguy.The worst part for emergency communications is the TOTAL loss of audio during heavy squalls or lightning strikes.Unlike the primitive NTSC system that's been 'improved' upon, any scrambling of ones and zeroes doesn't just results of streaks of noise in the video, it results in a total loss of audio.
Meanwhile, back at the NTSC Ranch, Major Armstrong's crude narrow band FM audio kept on doing what it always did. Perform . Reliably. :)

RJ
 
Re: Lightning Taking Out AM-HD Signals

Where the hell did this obsession with "digital broadcasting" come from, anyway?

I was watching digital HDTV (which of course is all we have now) in the over-the-air flavor at a friend's on a 40ish-inch Samsung flat-panel TV. It was tuned to a local station using typical indoors antenna, kind of an updated version of rabbit ears. Distance between the transmitter and receiver was about 3 air miles, station is full-power VHF.

At intervals not exceeding 5 minutes the program was interrupted with intermittent freezing and pixellating, with attendant audio muting. I tried reorienting the antenna without results. My friend advised, "that never helps." I asked, how can you watch this thing? He shrugged and said, "you get used to it."

IMHO this is NOT an improvement over analog. Sure, the picture is fantastic when it works - the problem is, it doesn't work reliably, and the freezing and reacquisition are vastly more disruptive to a quality viewing experience than an occasional ignition streak a la back in the good ol' analog days.

At this location, anyone with a $3 set of Radio Shack rabbit ears would have gotten a perfect, stable analog picture.
 
Re: Lightning Taking Out AM-HD Signals

Although I have digital cable, I also have an antenna connected to my Sony HDTV. It's in a window in my attic conversion essentially three story house, so it's basically a roof top antenna. It's a fairly high gain dual bow tie cavity backed unit that provides excellent off air reception. The picture is slightly better than the digital cable. How many "civilians" would know or bother to deal with something like this?
 
Re: Lightning Taking Out AM-HD Signals

Len, the visual carrier power in digital in many cases has tracked the former analog power although not strictly. One thing that has become apparent is that stations are discovering they need power increases - in some cases enormous ones - to get reliable digital coverage to replicate their former analog coverage. That's why there have been a flurry of power-increase apps for full-power TVs.
 
Re: Lightning Taking Out AM-HD Signals

I have a set top converter on a TV at our weekend farm location. It's located about 15 miles from the TV transmitters and in sight of the towers. Non-amplified rabbit ears work most of the time.

For the VHF-HD stations, most anything will interrupt the signals, including over flying airplanes. The close U's are a little more hardy, but for the weaker ones, movement near the antenna will disrupt the signal. An outside antenna is the only way to go in the TV digital mode (or satellite TV with the locals included in the package).

As to AM digital and lightning, an early observation from broadcasters was that lightning or any type of impulse noise would disrupt the signal. Of course a common form of impulse noise is auto ignition.
 
Re: Lightning Taking Out AM-HD Signals

I think about my grandmother who, back in the 60s and 70s, watched TV on her B&W RCA 630TS (as a recent widow she was a TV "early adopter") at her apartment in Batavia, almost precisely midway between Buffalo and Rochester. With minimal adjustment of garden-variety cheapo rabbit ears she could receive all six major network affiliates from both cities - 2, 4, 7, 8, 10 and 13, no problem.

If she had to install a 7-foot yagi, roof tower and rotator, Gram would have been what we call around here "a radio listener." She simply wouldn't have bothered.

OTOH: Gram had a big-time crush on Jack LaLanne and never missed her "morning exercises" with Jack. She was in great shape up until the end - all the older dudes thought she was pretty hot stuff. So who knows - she might have installed a free-standing tower and CATV grade amplifiers rather than miss those grainy 16mm LaLanne workouts.... ;)
 
Re: Lightning Taking Out AM-HD Signals

Savage said:
Where the hell did this obsession with "digital broadcasting" come from, anyway?

I was watching digital HDTV (which of course is all we have now) in the over-the-air flavor at a friend's on a 40ish-inch Samsung flat-panel TV. It was tuned to a local station using typical indoors antenna, kind of an updated version of rabbit ears. Distance between the transmitter and receiver was about 3 air miles, station is full-power VHF.

At intervals not exceeding 5 minutes the program was interrupted with intermittent freezing and pixellating, with attendant audio muting. I tried reorienting the antenna without results. My friend advised, "that never helps." I asked, how can you watch this thing? He shrugged and said, "you get used to it."

IMHO this is NOT an improvement over analog. Sure, the picture is fantastic when it works - the problem is, it doesn't work reliably, and the freezing and reacquisition are vastly more disruptive to a quality viewing experience than an occasional ignition streak a la back in the good ol' analog days.

At this location, anyone with a $3 set of Radio Shack rabbit ears would have gotten a perfect, stable analog picture.
Click to expand...

It seems digital broadcasting on radio or TV is not ready for "prime time" and may never be.

None of this could have happened if all forms of digital broadcasting had been thoroughly and impartially tested first, BEFORE being implemented. Unfortunately for everyone, it wasn't. It's still all a failed high school science project.

In an emergency we better learn to bend over and kiss ourselves goodbye. You won't get any warning, information, instructions or help from broadcasting or cable. All communications will be frozen, rebooting, buffering, squelched, hissed on, jammed, or otherwise unavailable.

Instead of reasonably reliable and simple analog, broadcasting has traded it's future for overly complex, unreliable digital.
 
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