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HD and Lightning

T

Those RRRRs

Guest
Is the HD AM Band affected by lightning like the terrestrial AM Band? And how is it that we can put a man on the moon but can't seem to "fix" the terrestrial AM Band so that the lightning problem no longer affects it? Or is it that no one has bothered to fix it?
 
If a few bits are missing, then no problem. If there are serious interruptions in the data stream (repeated loud crashes), then error concealment will no longer be possible, and the radio will drop back to analog reception, lighting crackles and all. Digital is kind of "all or nothing". You either get the full audio quality possible at a given bitrate, or you get nothing (nothing digital, anyway).

That's all the theory. I have no practical experience with AM HD. My GUESS is that an occasional lightning crash will cause no serious problem, but several of them in a few seconds and the deal's off. Am I wrong?
 
Both of the above are pretty fair one sentence answers and relatively accurate. I wrote the rest below and then got the "Others have posted" message. Maybe a little more detail will helo. If not... Oh Well.

Those RRRRs said:
Is the HD AM Band affected by lightning like the terrestrial AM Band? And how is it that we can put a man on the moon but can't seem to "fix" the terrestrial AM Band so that the lightning problem no longer affects it? Or is it that no one has bothered to fix it?
Click to expand...

I'm sure there ore others with a better explanation, but I'll start off and get you confused. :)
The difference is how the radio wave is changed to produce the sound.

You start with a radio wave on a certain frequency or wavelength and go from there. If you receive this wave with your radio... you get silence. Not "static" as in no station, but silence.

There are three other things you need to know to get how this works...

1) AM or AMPLITUDE Modulation, changes the amplitude or SIZE of the radio wave depending on what is being transmitted. Changes in the SIZE of the wave are detected by your good old AM radio and turned into sound. The louder the sound, the bigger the Amplitude or Size of the wave.

2) FM or FREQUENCY Modulation changes the Frequency of the radio wave depending on what is being transmitted. Small changes in the frequency of the wave are detected by your FM radio and turned into sound.

3) Lightning is (for lack of a better term) a giant electrical ZAP! It make a big amplitude wave across almost all of the radio bands.


So when AM is transmitting and FM is transmitting and there is a lightning CRACK... here's what happens...

A really Big "High Amplitude" wave is created by the lightning. It is on the AM band and on the FM band. Here's how your Kitchen radio on AM and your Office Radio on FM react to that big wave...

The Kitchen radio on AM reacts to the Really Big wave by making a really big sound. A Staticy sound, because unlike a song or voice, it's just really a really loud "Electrical" noise. As you know if you get close to the lightning strike it also makes a really loud SOUND as well. :)

The Office radio is listening to Frequency changes on FM. While it "can" become confused, it is looking for the Frequency changes in the radio wave it is listening to. If the Lightning put a really big wave over what the FM radio is listening to, it can overload your FM receiver and cause momentary confusion, but when an FM radio is confused, it tends to not see a frequency change and basically creates nothing Including static. If the lightning is furthur away, and the wave is not as big, it might not affect your FM radio at all.

As I understand it, the advantage (Such as it is) for HD is that it sends the data more than once (Which causes the delay). Since it sends it more than once, it has more than one chance to get it right. Therefore it is more RESISTANT to lightning. I would suspect AMHD is still affected by moderate storms (but better than analog) and FMHD is still affected by SEVERE storms (Tho better than analog).

It is ironic actually. We can put man on the moon, but I suspect we will NEVER conquer the static of mother nature.

I'll now gladly step aside and let the carreer engineers correct the finer points... (Or show me to be a complete numbskull.)

Clouseau
 
A really Big "High Amplitude" wave is created by the lightning. It is on the AM band and on the FM band. Here's how your Kitchen radio on AM and your Office Radio on FM react to that big wave...
Click to expand...

Modulation types aside, lightning affects the FM band (88 - 108 MHz) considerably less than the AM band (540 - 1700 kHz). Aircraft comms are in AM at frequencies just above the FM band (118 -137 MHz), and although static can be heard on those AM transmissions, the static is lower in comparison to what is heard on AM radio stations. Even 4-watt CBs at 27 MHz sound cleaner during storms than AM radio stations. This helps FM signals on the FM band be even more resilient to interference from lightning. Likewise, the HD Radio COFDM signals on FM are affected less by lightning than the HD Radio COFDM signals on AM (partially, anyway... bitrates/redundancy also plays a factor).

My experience with HD Radio on AM hasn't been as favorable as what others have posted here. With storms between 30 and 50 miles away, I lose the lock on HD signals for several seconds at a time repeatedly. This is for the 50kW powerhouses that sound clear and virtually static-free in analog mode. My receiver is the Sangean HDR-1 using the stock loop antenna. During the same storms, the HD Radio signals on FM have always been solid.
 
My experionce with HD-am lightling, is if there is a lot around, it cuts off the hole signal but my nearest signal is WOAI about 60 miles from me so that might be a factor there.
 
Mike Walker said:
That's all the theory. I have no practical experience with AM HD. My GUESS is that an occasional lightning crash will cause no serious problem, but several of them in a few seconds and the deal's off. Am I wrong?
Click to expand...

I've listened extensively during thunderstorms, and you are correct. If the lightning crash is at least 20 dB or so below analog carrier, it will disrupt the digital decoding process and cause the receiver to "blend" from digital to analog for a couple of seconds. As long as the crashes are occasional, the diversity delay will usually prevent them from being heard, but in a moderate to severe storm, the receiver will remain in analog mode, thus the digital signal is of no benefit.
 
I actually think it's kinda neat hearing lightning on AM radio, and I don't mind it at all. Of course, I come from an area that has thunderstorms maybe 3-5 days a year so it's a rare and interesting occurrence to be able to hear the lightning. On an all digital system it would either sound like nothing at all or like rebuffering errors on internet radio - boring!
 
awj223 said:
I actually think it's kinda neat hearing lightning on AM radio, and I don't mind it at all. Of course, I come from an area that has thunderstorms maybe 3-5 days a year so it's a rare and interesting occurrence to be able to hear the lightning. On an all digital system it would either sound like nothing at all or like rebuffering errors on internet radio - boring!
Click to expand...

Yea, me too - always enjoyed thunderstroms, while listening to DX AM. Looks like Mike has figured out that even on HD-FM the digital signals crash.
 
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