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AM IBOC during electrical storms in NYC

L

LinoNYC

Guest
I've had an Acurian IBOC radio since last November, yeaterday during an electrical storm here in NYC I decided to hear how this system delt with interference on the AM band.

The Acurian has a set of 6 "bars" corresponding to the strength and buffer level of digital data and I have noticed that this level will often vary slightly during normal conditions.

Storms create more dramatic variations.

Using the supplied loop antenna positioned for optimum under normal conditions:

WOR (strongest AM in area) 6 Bars no changes during storm.

WABC Normally varies 4-6bars. During strorm it varied down to 2 but did not revert to analog

WNYC Normally 3-5 bars Reverted to analog several times a minute due to lightening.

WCBS-am Slightly weaker in this area than WNYC usually no more than 2 bars often no digital lock at all. During storm: call letters appeared but no digital.

Although I have read that this system would render AM largely immune from interference it seems that in order for this to be possible, this signal must be nearly strong enough to overcome noise even in analog.

This probably explains why two small stations, WPAT-am and WZRC seem to have discontinued IBOC transmissions two years ago. I don't understand why WADO (Spanish-50K) ceased late last year.


Lino
 
50.000 watt KLAA Orange, CA at 830 AM dropped HD radio a year ago and never looked back. I suspect the list is growing.
 
My own experience with Chicago stations during storms is similar to yours in NYC. My Sangean HDR-1 repeatedly loses HD lock on 19-mile-distant WLS, yet the analog audio from WLS remains clean. The storms don't have to be on top of me, either. HD on the FM band remains rock-solid even with lightning strikes a block away.
 
Ok, one more time.

Scotty said to Kirk, "I canna change the laws of physics".

Neither can iBiQuity.

The reason why there was a noticeable effect from lightning on AM IBOC reception but not on FM IBOC reception is because noise from lightning affects a signal's AMPLITUDE (not its FREQUENCY). If the data on an AM signal is trashed because of lightning noise and bits are lost or scrambled then your AM HD receiver is going to "blend to analog". This will not happen on your FM HD receiver because lightning causes no interference whatsoever to the frequency of a signal.

It's amazing what corporate propaganda people will believe, isn't it?
 
Cal Stymes said:
The reason why there was a noticeable effect from lightning on AM IBOC reception but not on FM IBOC reception is because noise from lightning affects a signal's AMPLITUDE (not its FREQUENCY). If the data on an AM signal is trashed because of lightning noise and bits are lost or scrambled then your AM HD receiver is going to "blend to analog". This will not happen on your FM HD receiver because lightning causes no interference whatsoever to the frequency of a signal.
Click to expand...

You're on the right track here, but I'm obligated to mention that both the AM and FM digital carriers employ a combination of amplitude and angle (frequency) modulation.

However, the laws of Physics still apply: AM HD doesn't tolerate lightning well because a huge interrupted-DC spark throws much more energy into the medium-wave band than the VHF range where FM stations operate. (Most small power line insulator arcs also concentrate their RF energy at lower frequencies, the noise can be carried hundreds of meters along the wires.)

Also, the AM IBOC scheme relies on 64-QAM digital subcarriers, which have less noise immunity than the BPSK or QPSK signals used for FM because the digital symbols are closer to one another in phase and amplitude. So when noise is factored in, there is a greater probability of decoding errors -- and when these rise above the capability of the system's forward error correction algorithm, the receiver gives up and blends back to analog. For a detailed explanation of the differences, see:

http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation#Digital_QAM

http://en.wikipedia.org/wiki/Phase-shift_keying
 
The HD radio cartel's claims of noise and interference immunity are just another HD radio deception?
Well, imagine that!
 
Cal Stymes said:
The reason why there was a noticeable effect from lightning on AM IBOC reception but not on FM IBOC reception is because noise from lightning affects a signal's AMPLITUDE (not its FREQUENCY). If the data on an AM signal is trashed because of lightning noise and bits are lost or scrambled then your AM HD receiver is going to "blend to analog". This will not happen on your FM HD receiver because lightning causes no interference whatsoever to the frequency of a signal.

It's amazing what corporate propaganda people will believe, isn't it?
Click to expand...

You are dead right about Amplitude Modulation versus Frequency Modulation. However, we are talking about Coded Orthogonal Frequency Division Multiplexing versus Coded Orthogonal Frequency Division Multiplexing.

Yes, I intentionally repeated myself, because HD Radio is transmitted via COFDM on both the "AM Band" and the "FM Band." You can transmit AM, FM, or COFDM at any frequency.

Several factors come into play. Although COFDM is used on both bands, it is not transmitted in a 100% identical manner. One difference is the wider channel spacing between 88 - 108, which allows the COFDM signal to be spread much wider. Another difference is that the COFDM signal on the AM band is linked to the AM carrier to some degree, and RFI disrupts that relationship.

Yet another significant difference is that 530 to 1700 kHz is FAR MORE susceptible to electrical interference than 88 - 108 MHz. Evidence of this is the dramatic difference between commercial AM radio stations and VHF aircraft AM stations. During a storm, even a 50kW AM radio station can be virtually unlistenable, but a 100w aircraft ATIS station (118 - 136 MHz) is very much readable, with subdued static. Electrical noise is further reduced in the military aircraft band, located between 225 and 400 MHz, which also uses AM.

I once worked at GTE Airfone, which operated in AM in the late 80s. I NEVER heard lightning static over those units. They operated at 849-851 and 894-896 MHz.
 
I stand corrected that lightning (high voltage DC-spark) interference is more of a frequency band phenomenon than a modulation type phenomenon.

Thank goodness we have all you experts on here to set the record straight! :)
 
The Dude said:
vsa said:
50.000 watt KLAA Orange, CA at 830 AM dropped HD radio a year ago and never looked back.
Click to expand...
VERY GOOD!!!!!!!!

WE NEED MORE STATIONS TO DO THE SAME!
Click to expand...

WLS 890 was hissless one day about two weeks ago, presumably for upgrades, as all the other iBOC had similar one-day outages.

This morning on the way to work, WLS had no iBOC, WGN and WBBM did. Guess who got the hour of TSL?
 
vsa said:
50.000 watt KLAA Orange, CA at 830 AM dropped HD radio a year ago and never looked back. I suspect the list is growing.
Click to expand...

The ONLY other station to do that was 560 WIND due to an ownership change. OK that is two compared to how many have added it?
 
cmenow said:
vsa said:
50.000 watt KLAA Orange, CA at 830 AM dropped HD radio a year ago and never looked back. I suspect the list is growing.
Click to expand...

The ONLY other station to do that was 560 WIND due to an ownership change. OK that is two compared to how many have added it?
Click to expand...

Seems there was one in NJ that dropped the AM iBOC. Clifton, Nutley, Passaic, somewhere in that area.

Lunchtime update from NW suburban Rolling Meadows, IL. More AM iBOCs missing in action at lunchtime....

890 AM WLS is still analog only. Bandwidth seems like it's still limited but has "oomph". More ibquity upgrades?
WGTO 910 Cassopolis MI is clearly audible here 25 miles inland, playing Hey Jude. WOKY Milwaukee next door on 920 is running iBOC,
but the sidebands on 910 are at the very threshold of detection, not too bad.

620 WTMJ Milwaukee is running a Brewer's game, and it's in analog only. Upgrades?

670 WSCR Chicago is also analog only.

If these are all upgrades being installled, we'll know soon enough.
 
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