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Is HD-AM Night-time 'Fixed' Yet?

J

JohnnyElectron

Has iBiquity been able to modify their system yet to allow the W-call 50KW clear channels on 750/760/770 and 890 to fire-up IBOC at night again? I haven't heard any activity after sunset from WJR and its brethern yet, and I'm curious if the Citadel stations will just run at a reduced digital carrier sometime in the near future to restore night-time HD-AM service?
 
With many 50kw AMs reporting reliable HD coverage extending barely 25 miles, and penetration of steel-frame buildings already virually nil, reducing the digital carrier injection level is likely to render the HD coverage meaningless. This is especially true at night when the HD has to contend with skywave interference.

Barry McLarnon, feel free to chime in on this, but you calculated that reliable HD decode under typical skywave conditions would require a signal strength of about 36 mv/m, if I recall. Maybe he'll share with us how he arrived at that figure. Assuming that to be the case, even a 6db reduction would seriously compromise HD performance.

Then there are the cases of major AMs with critical tuning networks and very deep nulls which simply will not work with IBOC-AM, without a complete rebuild of the phasor and LTUs. And special cases such as KDKA, where the pattern bandwidth of their stacked "Franklin" NDA tower is so asymmetrical as to make HD implementation impracticable.

If a nighttime "fix" was possible with simple tinkering of injection levels, this would have been accomplished long before this.
 
JohnnyElectron said:
Has iBiquity been able to modify their system yet to allow the W-call 50KW clear channels on 750/760/770 and 890 to fire-up IBOC at night again? I haven't heard any activity after sunset from WJR and its brethern yet, and I'm curious if the Citadel stations will just run at a reduced digital carrier sometime in the near future to restore night-time HD-AM service?
Click to expand...

It cannot be fixed. The only way to "fix" it is to shut it down, or live with mutual jamming. The AM system is defective from the start and should never have been implemented.
 
I was being diplomatic in the earlier post. Bruce is right. The sideband interference stomping on (at least) first-adjacents is inherent because with IBOC-AM the analog and digital must co-exist within an insufficient and narrow medium-wave channel. If you reduce digital injection, you further reduce already-marginal HD coverage and building penetration. If you set the digital carriers either side of the analog carrier asymmetrically to reduce interference in this sideband or that one, the asymmetry shows up as unacceptable noise increases in the analog component (and more problems with digital decode.) Further reduction of analog bandwidth past the current practice of about 5 kHz is not practicable because the analog component has already been compromised too much to suit the tastes of most listeners (and the oft-repeated "all receivers are narrower than that anyway" argument is a fallacy, as has been argued here many times before.)
 
Savage said:
With many 50kw AMs reporting reliable HD coverage extending barely 25 miles, and penetration of steel-frame buildings already virually nil, reducing the digital carrier injection level is likely to render the HD coverage meaningless. This is especially true at night when the HD has to contend with skywave interference.

Barry McLarnon, feel free to chime in on this, but you calculated that reliable HD decode under typical skywave conditions would require a signal strength of about 36 mv/m, if I recall. Maybe he'll share with us how he arrived at that figure. Assuming that to be the case, even a 6db reduction would seriously compromise HD performance.

Then there are the cases of major AMs with critical tuning networks and very deep nulls which simply will not work with IBOC-AM, without a complete rebuild of the phasor and LTUs. And special cases such as KDKA, where the pattern bandwidth of their stacked "Franklin" NDA tower is so asymmetrical as to make HD implementation impracticable.

If a nighttime "fix" was possible with simple tinkering of injection levels, this would have been accomplished long before this.
Click to expand...

Sure, it's all right here on the back of this envelope. :) Actually, I already explained my calculation in my earlier message on the subject. Hopefully, this will link to it:
http://www.radio-info.com/smf/index.php/topic,82698.msg616177.html#msg616177

Barry
 
Yup.. One can't fix what's unfixable. The only FIX for IBUZ AM digital is to go to virgin spectrum somewhere, and preferably adopt DRM instead. Either the current channel 6 TV band, the 26MHz RPU band, or maybe even trying to ask for something like 1700-1800 for local IBOC would make some sense. In a way the 1700-1800 would make the MOST sense as stations could just diplex it in their current array and go with it. (with some work, of course.) At a very minimum we need to DEMAND that all digital radios from now on are capable of also getting DRM so when and IF there are enough radios to get digital-only in the future we can go with a standard that WORKS.
 
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