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The Effect of Degradation to Analogue Coverage by IBOC

We are parsing this on the DFW board. Never hear this before. Any thoughts?
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There is another aspect of HD that is troublesome. It digs deep into the analog coverage range. KGLK Lake Jackson was a very useful test station, because their HD would be on, then off, then on, etc. Since I make the Dallas / Houston drive frequently, I am familiar with how far the stations go. Prior to any HD, there was a good dividing line at about Centerville. Some went a little farther, some less. But it was - Buffalo - all Dallas. Madisonville, all Houston. Average days year round no skip.

KGLK ran HD, its Northern coverage shrank from Centerville to South of Huntsville. That is HUGE. Because of their frequent shutdowns, I could tell you by Centerville if they were running HD or not - as confirmed by interference on first adjacents. Now they probably don't care much about Centerville, Madisonville, and Huntsville but I guarantee they care about the Woodlands and Conroe, where they would no longer come in on cheap radios. I can prove the care about those markets because they bought 106.9 to cover them again. When all they really needed to do is just shut down HD. And it also has a big impact on building penetration closer in.

So how do Dallas FM's fare? Somewhat better, but their range is still drastically affected. What used to be down to Centerville and in a lot of cases Madisonville is now between Fairfield and Buffalo. Pretty much every DFW since HD was adopted. Still - not serious if you consider Buffalo ratings, but building penetration in downtown Dallas is another matter. I challenge any DFW station engineer to take the drive themself, test the range with HD on, then test it with HD off at a similar time of day. It is repeatable and a profound shrink of range.

I get the same on Houston stations, virtually all are gone just North of Huntsville now.

So the key takeaway from this is that on average what used to be 130 to 140 miles is now 80 to 90, which is not much more than HD reception range of 70 miles. So from blended mono at 90 miles to full HD reception at 70 miles is the new norm. Not bad if you are after an HD system that matches analog coverage, but analog coverage has been gutted in the process. I make this drive a lot, I discount ranges late in the evening and early morning, but mid day it is absolutely repeatable and a stunning indictment of the engineering involved in setting up this system. Bad engineering through and through.
 
Okay, that's a biggie. I'll need some time to dig in and think about the big picture as to why.

Here's a synopsis of what you're saying very concisely for the less technical minded (yes, for the GM's following!):

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1) IBOC activation/operation noticeably degrades the usable coverage radius of analogue FM.

2) You have observed this along I-45 between Houston and Dallas.

3) While degradation of the absolute coverage radius along the I-45 corridor is negligible, the corresponding degradation of coverage radius along desired azimuths, in the direction of desired outlying population in any respective market, is highly critical. (negative implications for Conroe & Woodlands in the case of Houston)

4) Accordingly, the degradation to analogue FM signal strength caused by IBOC operation has a serious and direct consequence that requires separate, special consideration for inner city building penetration. (critical negative effect for downtown and other in-building office listeners)
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Wow, that is an astonishing observation that I have never, ever heard before.

My gut reaction says to act to quantify this with repeat measurements using two test stations of known integrity (operating at verified 100% ERP each time), one in Dallas and another in Houston.

So, get two stations from the same group owner, turn IBOC off and complete multiple runs using an Audemat or similar mobile measurement system to collect signal strength data for analogue only operation.

Basically, drive from Cedar Hill to Missouri City, and measure the same two stations say seven separate times, analogue only.

Then perform a separate set of seven Dallas to Houston runs for the same stations with IBOC activated.

Take all of the data sets and perform basic statistical analysis - at minimum, discard statistical outliers, compare and contrast averages, maxima and minima of signal strength to determine benchmark locations (the contour radius) for the two stations operating in both IBOC On and IBOC Off conditions to draw a quantitative conclusion.

Doing this would enable you for sure to see the location of various contour radius(s) for signal thresholds (70, 60, 50, 40 dBu) which would in turn allow you to roughly estimate the effect of reduction in analogue ERP when operating in IBOC.

Okay, let's say we've got the data... who ya gonna call? Ibiquity? Nooo. We would need a consultant from Gerogia Tech's rad lab to validate everything.
 
There are some other things to consider about FM "HD" radio and how stations choose to implement the service. Many stations choose to go with "spacial combining", which consists of either separate antennas or going with a different circular rotation within the same antenna through a additional port/coax run. I feel either of this "solutions" are problematic as ensuring that digital vs. analog proportions cannot be as easily assured. In my market, there are several that are combined via an ERI COG antenna system, feed with separate coax runs for analog and digital that rotate into the antenna with opposite directions. I personally have observed that when I take the whip antenna and move it various directions I can make the digital carriers LARGER than the analog in some positions. Add to this that the antenna has a ton of gain and it's in part of the metro. Null fill doesn't totally fix all the problems that are within the first few miles. Are some of the highest rated stations in town coming out of it? Yes. Is it a perfect signal? HELL no. Another thing to consider is that many "HD" stations were put on the air and not really maintained properly. Many do not have the more automatic adaptive corrective system that newer units are now coming out with. I guess what I'm saying is there are PLENTY of reasons why the HD can and DOES screw up the analog signal IF things aren't set up and adjusted right. The days of chisels, hammers, screw drivers, DMM, and a soldiering iron being the only tools needed to do are job are far over. Knowledge, care and the proper test tools to be able to see if a station is set up right and is meeting the mask are VERY, VERY important.
 
ERI COG antenna system, feed with separate coax runs for analog and digital that rotate into the antenna with opposite directions

I am familiar with COG Wheel Master Antenna System; Senior Road Tower put one up. I like to call the opposing LH & RH analog and digital circular polarizations "contra-rotating cp"... borrowing that name from the Tupolev Tu-95 Soviet BEAR Bomber which has contr-rotating propellers, which helps me visualize the opposing CP for each service.

And I do agree that there are many, many transmission system and antennae system variables in play that must be considered, narrowed and eliminated before conducting any real time measurements.

-Type of Amplification
-Type of Combining
-Type of Antennae System (to name a few).

But if one station in Dallas and a second in Houston had substantially similar plants, the same type of amplification, combining and antennae systems, it would be a good situation to quantify the difference analogue performance for analogue only versus analogue + digital operation to see if turning on the digital impinged on the analogue signal strength in any statistically meaningful way.

I don't know that I would trust an Audemat Navigator for precise measurement and characterization at this level. I'd use the Z-Technologies field strength meter instead.

I really feel that Ibiquity's attempt to quantify the level of RF needed to yield a comparable IBOC coverage area, including being realistic about IBOC building penetration, was either insufficient or very seriously flawed. Accordingly, it wouldn't surprise me if Ibiquity gave little, no or insufficient attention to impingement of analogue coverage.
 
I'm sure if glossing over something like that made them more money, they'd surely do it. Everything I've seen from them so far pretty much points that way. Let's face it... Their AM product is nothing short a joke on the industry. So I think your thought that they might just try to ignore a defect of the system is pretty safe bet.
 
I am cynical enough to believe that a desired outcome of the introduction of "digital modes"
is to eliminate the memory of 140 mile reception eventually.
 
Tom Wells said:
I am cynical enough to believe that a desired outcome of the introduction of "digital modes"
is to eliminate the memory of 140 mile reception eventually.
Me too Tom
 
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