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HD in new cars

tomservo said:
So, what's the deal with the so-called "extended hybrid mode" I've heard about before… just fiction?
Click to expand...

There is only so much real estate to put your digital carrier inside of and 196kbps to do it with, so extending is not an option.

Some stations run asymmetrical HD because of an adjacent station on one side of their carrier. All that is involves is shifting higher digital carrier power to one side of the channel and lowering the one closest to the adjacent station.
 
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DavidEduardo said:


I have never heard of that. Have you any reference, description or link? Perhaps it is just promotional hype or a name for pure digital broadcasting without the analog component (just guessing).
Click to expand...

http://hdradio.com/broadcasters/engineering-support/high-quality-consistent-multicast-engineering

There are two FM modes available to use when multicasting:

MP1 Mode has a usable bandwidth of 96 kbps and is referred to as the Hybrid mode.
MP3 Mode has a usable bandwidth of 120 kbps and is referred to as the Extended Hybrid mode.
The table below shows how the multicast channels can be divided depending on the station’s programming needs.
(A table follows, visible on the page as a graphic)


Maybe this is something like the "hierarchical modulation" Sirius XM introduced a few years ago as a way to cram more channels into limited bandwidth. Those channels, about 50 of them, are only available online and on a few radio models.
 
CTListener said:
http://hdradio.com/broadcasters/engineering-support/high-quality-consistent-multicast-engineering

There are two FM modes available to use when multicasting:

MP1 Mode has a usable bandwidth of 96 kbps and is referred to as the Hybrid mode.
MP3 Mode has a usable bandwidth of 120 kbps and is referred to as the Extended Hybrid mode.
The table below shows how the multicast channels can be divided depending on the station’s programming needs.
(A table follows, visible on the page as a graphic)


Maybe this is something like the "hierarchical modulation" Sirius XM introduced a few years ago as a way to cram more channels into limited bandwidth. Those channels, about 50 of them, are only available online and on a few radio models.
Click to expand...

Aha! That explains it. The graphic puts it into perspective. Stations can have up to three total channels in MP1 mode or MP3 mode. I bet my local iHeart station that's running 3 channels is in the MP3 mode; on the SDR the sidebands are noticeably wider than the other stations in the market.
 
I hate to differ with DE, but I had that same issue many years ago.
A CBS Radio engineer explained that a higher numbered sub-channel can be closer to the analogue sidebands than the HD1 & 2,
but I cannot remember the details.
Apparently, the receivers are actualy tuning into more than one digital stream.

"The Sound of The Strip" is on KJKK-HD2(100.3), Dallas,
and was on WEAT-HDsomething(104.3), West Palm Beach
 
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ai4i said:
A CBS Radio engineer explained that a higher numbered sub-channel can be closer to the analogue sidebands than the HD1 & 2,
but I cannot remember the details.
Apparently, the receivers are actualy tuning into more than one digital stream.
Click to expand...

Either that engineer was mistaken, or you maybe misunderstood. The data streams for all HD channels are really one stream. The bits for all HD channels are encoded into that single data stream which occupies space on each side of the analog carrier. There is no physical spacing that puts an HD-3 channel closer to another station. What does happen, is the number of bits assigned to an HD3 channel will be less than an HD2 channel, or equally divided between HD2 and HD3. As has been discussed before, HD2 and 3 channels don't have enough bandwidth to provide Forward Error Correction (repeating of bits in case they get dropped in reception).
 
Kelly A said:
You covered most of the antenna variables David. Depending on the installed overall transmission system and how well maintained, one can also factor in things like AM noise levels (synchronous or asynchronous) and total group delay through the system. The fact is that some stations pay more attention to their installation design and maintenance, while others just do the minimum.

As David did say rightfully though; 50% of reception quality is at the point of reception.
Click to expand...

I think we are in agreement for once. Come to think of it - the reception dropout on Tuckerton is also an area that floods when it rains. In other words - a low spot. Sure, you can see the towers at night, but it is substantially lower in elevation. So - something blocks it just a bit, a lot of house, a water tank, who knows. The whole antenna farm is blocked, so pretty much everything drops out of HD. All of the variables sound reasonable, but there is good evidence that most antennas are done by the same outfit, so they probably buy antennas in bulk from one manufacturer. The aiming is straightforward - North. Nothing but farms, small towns, and the Gulf the other direction. And somebody told me that 35 years ago when they installed the antennas, they did it to throw nulls up the freeways. Pretty precise aiming ----. Antenna height, pretty much all 2000 feet. Several towers, but 20 miles away they are all pretty much together when you get 20 miles away. A few degrees at most.
 
Kelly A said:
Either that engineer was mistaken, or you maybe misunderstood.
Click to expand...
The following is consistent with what he explained:
"Analog FM modulation should be kept within the FCC allowed limits;
excessive audio processing and/or over-modulation will decrease the performance of the IBOC extended subcarriers."
It was the heavy processing that presented the issue.
 
rbrucecarter5 said:
All of the variables sound reasonable, but there is good evidence that most antennas are done by the same outfit, so they probably buy antennas in bulk from one manufacturer.
Click to expand...

There are several manufacturers of FM transmission antennas, and each has several models with extensive customization options, such as the degree of beam tilt, etc.

Also an option is the number of bays. Most of us prefer the lowest number of bays possible as more bays produces nulls in the horizontal lobe that can create a ragged coverage pattern. The best example was the 110 kw operation of KPFK on Mt Wilson in lA: a 12 (or was it 14 :mad:) bay Shively. It left big zones of ratty signal in between zones of good signal, like a big layer cake.

At the lower end of number of bays, the restriction is the TPO into the coax: there is a point where neither the cost of electricity nor the cost of the transmission equipment is feasible. Two Nautel 80's, anyone?

Each single-station antenna is custom built and tuned to the station frequency. Generally, big market stations pay for field testing on a tower section that is the same as the intended support structure, as the tower cross section dimensions have a big effect.

Master or multi-station antennas have another set of issues. Likewise for single station panel antennas.

It's not the same as pulling a yagi out of a box.

The aiming is straightforward - North.
Click to expand...

No, it is not that simple.

And somebody told me that 35 years ago when they installed the antennas, they did it to throw nulls up the freeways.
Click to expand...

Cowabunga, Buffalo Bob.

Pretty precise aiming ----. Antenna height, pretty much all 2000 feet. Several towers, but 20 miles away they are all pretty much together when you get 20 miles away. A few degrees at most.
Click to expand...

This should be the dictionary example of oversimplification of a false premise.
 
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DavidEduardo said:


There are several manufacturers of FM transmission antennas, and each has several models with extensive customization options, such as the degree of beam tilt, etc.

Also an option is the number of bays. Most of us prefer the lowest number of bays possible as more bays produces nulls in the horizontal lobe that can create a ragged coverage pattern. The best example was the 110 kw operation of KPFK on Mt Wilson in lA: a 12 (or was it 14 :mad:) bay Shively. It left big zones of ratty signal in between zones of good signal, like a big layer cake.
Click to expand...

Am I correct that more bays = more ERP from a lower powered transmitter = lower electric bills?

The place that is most ridiculous on bays is Roswell. Every little rise west of town has a tower a few hundred feet high with many bays extending almost the height of the tower.
 
rbrucecarter5 said:
Am I correct that more bays = more ERP from a lower powered transmitter = lower electric bills?
Click to expand...

More bays means more of the TPO concentrated in the horizontal plane, rather than going at angles above the horizon or straight down at the ground in the area of the transmitter.

There are disadvantages once you have too many bays, such as the serrated radiation pattern in the narrower beam which can produce all kinds of erratic coverage issues.

The place that is most ridiculous on bays is Roswell. Every little rise west of town has a tower a few hundred feet high with many bays extending almost the height of the tower.
Click to expand...

Larger market stations consider power bills to be a relatively minor expense. But in tiny markets, they can be significant, as can the cost of maintaining a higher power transmitter.
 
DavidEduardo said:


More bays means more of the TPO concentrated in the horizontal plane, rather than going at angles above the horizon or straight down at the ground in the area of the transmitter.

There are disadvantages once you have too many bays, such as the serrated radiation pattern in the narrower beam which can produce all kinds of erratic coverage issues.



Larger market stations consider power bills to be a relatively minor expense. But in tiny markets, they can be significant, as can the cost of maintaining a higher power transmitter.
Click to expand...

I suppose that having more power on the horizontal plane can help when a station is stuck with a less than ideal tower site far from the community they want to serve? Seems like the only time I've seen 8 or 12 bays on a tower it's been in the boonies, far from a city.
 
tomservo said:
Seems like the only time I've seen 8 or 12 bays on a tower it's been in the boonies, far from a city.
Click to expand...
...and in earlier instalations.
Large arrays were popular during the horizontal-only days.
Look at this GIANT early array in Poundridge, NY!
 
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ai4i said:
...and in earlier instalations.
Large arrays were popular during the horizontal-only days.
Look at this GIANT early array in Poundridge, NY!
Click to expand...

Jeez. That is one odd tower. Like a Blaw-Knox with another tower on top!

The first site I think of when remembering a site with a lot of bays is WGNL in Greenwood, MS. I used to drive by the tower site 2-3x a week and since it was right by the road and on a short stick (~340 feet AGL) it looked massive. I tried to find a Google Street View of the site as it exists today but it looks like the tower has been abandoned since 2014 (FCC coordinates still show it in use, so…?) This 2013 Street View shows the bays but they don't look that impressive from the highway. In person it always looked much more "substantial".

I never noticed any weird signal issues with the station, at least not in the flat as a pancake MS Delta region. Up in the hills it deteriorated quite quickly despite being only 10-20 miles from the site, but that was also on the back side of the antenna.

Since the OP was about HD radio technology, I'd hate to see how such a spiky pattern from one of these monsters would mess with HD signal strength. I bet it would make reception even more problematic.
 
tomservo said:
Jeez.
Click to expand...
...yes, and before they were able to get FAA approval to extent their tower an extra ninety feet,
they had all of their FM elements mounted on the side of that very same Blau-Knox, here.
 
ai4i said:
The following is consistent with what he explained:
"Analog FM modulation should be kept within the FCC allowed limits;
excessive audio processing and/or over-modulation will decrease the performance of the IBOC extended subcarriers."
It was the heavy processing that presented the issue.
Click to expand...

They're talking about the extended subcarrier within the channel being the digital or analog sidebands (HD Radio/SCA), being adversely effected by exceeding analog modulation limits. For example, if you exceed 75kHz deviation of your analog carrier, you risk running into, or overlapping into the real estate of the digital HD radio carriers or analog SCA, like one you'd find at 67kHz.
 
rbrucecarter5 said:
Am I correct that more bays = more ERP from a lower powered transmitter = lower electric bills?

The place that is most ridiculous on bays is Roswell. Every little rise west of town has a tower a few hundred feet high with many bays extending almost the height of the tower.
Click to expand...

As David mentioned, all major or mid market stations aren't concerned with trading antenna gain to save money, but to find the best combination of gain over TPO.

If you isolated a single circularly polarized FM antenna dipole (bay) and looked at the radiation pattern, it would look essentially like a sphere. Equal radiation going in all directions. Stacking elements focuses the radiation toward the horizon. The physics are that in that process, and depending on the amount of antenna gain, there are even order nulls that fall along the antenna field in some directions. Some of the nulls are less or deeper than others, because the antenna is mounted on a steel tower with potentially other antennas providing certain amounts of re radiation and reflection.
 
Kelly A said:
As David mentioned, all major or mid market stations aren't concerned with trading antenna gain to save money, but to find the best combination of gain over TPO.

If you isolated a single circularly polarized FM antenna dipole (bay) and looked at the radiation pattern, it would look essentially like a sphere. Equal radiation going in all directions. Stacking elements focuses the radiation toward the horizon. The physics are that in that process, and depending on the amount of antenna gain, there are even order nulls that fall along the antenna field in some directions. Some of the nulls are less or deeper than others, because the antenna is mounted on a steel tower with potentially other antennas providing certain amounts of re radiation and reflection.
Click to expand...

Actually - the owner of WAPN (who was eaten up with diabetes and had mood swings) located a very old 6 kW transmitter and insisted on firing it up using a single bay. With losses he would be in his licensed 2.2kW power. This was an exceptional opportunity to hear what a station will do with a single bay. The most striking thing - there was no picket fencing in the fringes. It was like driving over a cliff - one mile it was there, the next mile it was gone. No back and forth. The fact that there were other 91.5's in Orlando and Cocoa Beach meant that WAPN would clear on I-4, and the 91.5 from Orlando would immediately come in, with no swapping between the two. But Orlando and Cocoa would swap.

That was a short-lived experiment. He took one look at the electric bill, and changed back to his original configuration of a much smaller, more efficient 900W transmitter off of four bays, which only put out 1800W ERP, but his electric bill was once again fully supported by the preachers dropping off their cassette tapes for airplay. Very shoestring operation. I never had to climb the tower (like the guy on the show before me) to get the station back on the air, but I did have to swap the germanium transistors in the very old exciter to get my show on the air. That 1800W off of 300 feet actually had listeners in Keystone Heights and the south part of Jacksonville, but only when we were on the air with relevant programming. 80 miles is pretty good off of that setup.
 
rbrucecarter5 said:
Actually - the owner of WAPN (who was eaten up with diabetes and had mood swings) located a very old 6 kW transmitter and insisted on firing it up using a single bay. With losses he would be in his licensed 2.2kW power. This was an exceptional opportunity to hear what a station will do with a single bay. The most striking thing - there was no picket fencing in the fringes. It was like driving over a cliff - one mile it was there, the next mile it was gone. No back and forth. The fact that there were other 91.5's in Orlando and Cocoa Beach meant that WAPN would clear on I-4, and the 91.5 from Orlando would immediately come in, with no swapping between the two. But Orlando and Cocoa would swap.

That was a short-lived experiment. He took one look at the electric bill, and changed back to his original configuration of a much smaller, more efficient 900W transmitter off of four bays, which only put out 1800W ERP, but his electric bill was once again fully supported by the preachers dropping off their cassette tapes for airplay. Very shoestring operation. I never had to climb the tower (like the guy on the show before me) to get the station back on the air, but I did have to swap the germanium transistors in the very old exciter to get my show on the air. That 1800W off of 300 feet actually had listeners in Keystone Heights and the south part of Jacksonville, but only when we were on the air with relevant programming. 80 miles is pretty good off of that setup.
Click to expand...

A single bay is "overkill" in the search for raw power vs. antenna gain.

Different engineers have different criteria. Something in the 4 to 6 bay range seems the favorite for higher power stations (B and C Class) while two bays seems to be the optimum for Class A stations.

I did a lot of experimentation with antennas at my first FM. Since it was the first FM in the country, there were no technical rules so we tested many alternatives, making the antenna elements out of stuff from our local plumbing supply house. We ended up with a vertically polarized two bay antenna with severe mechanical beam tilt and a screen reflector at the back of the tower which was at about 13,000 feet AMSL on a mountainside. That combination produced the best coverage, the least multipath and the best penetration in a market where most construction was either masonry or concrete with rebar construction.

My preference would be 4 bays and more pure power. Since no two sites and no two towers are the same, it is hard to have "proof" but over the years that has proven to be the best combination for both nearby and fringe reception.
 
For transmitter sites located in downtown areas, lower gain and higher TPO may be best because you have listeners under-or in the vicinity of the antenna. For mountaintop sites or sites at least 10 miles from the metro, higher gain puts field where the population is. Using low gain in areas where there is nobody close in, is IMHO, a waste of energy.
 
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