How does a receiver identify an AM HD broadcast?

[bulwnkl]

Okay, my question is different and more specific than the title seems. (-:

I understand that HD transmissions are much lower power than analog, and have read that one should not expect to receive distant AM HD signals. However, when I tune KSL (about 500 miles away, straight-line, according to a website), the radio shows me that there's an HD signal there for several seconds. It even initially identifies the station as "KSL-HD." However, after a few seconds, that goes away. It never snaps over to the digital HD signal at any time, but the radio seems to 'know' the HD signal is there.

Do I misunderstand how far an AM HD signal will travel? I thought there would be no possibility whatever of KSL's HD signal reaching me, but I guess it must be getting here, just very weakly?

 

[rbc]

With hybrid AM HD, the HD broadcast is on the edges of the analog signal, not getting as much power as the analog signal. Sometimes the HD radio detector can find an HD signal, even if it can't decode it. In Mississippi, I've received HD carriers from WSCR, WBBM, and KRLD. I've only successfully decoded WBBM once it my car when the sky-wave was coming in strong. I have a video of that:

https://www.youtube.com/watch?v=v9tQDfZRj3Y

 

[KeithE4]

Okay, my question is different and more specific than the title seems. (-:

I understand that HD transmissions are much lower power than analog, and have read that one should not expect to receive distant AM HD signals. However, when I tune KSL (about 500 miles away, straight-line, according to a website), the radio shows me that there's an HD signal there for several seconds. It even initially identifies the station as "KSL-HD." However, after a few seconds, that goes away. It never snaps over to the digital HD signal at any time, but the radio seems to 'know' the HD signal is there.

Do I misunderstand how far an AM HD signal will travel? I thought there would be no possibility whatever of KSL's HD signal reaching me, but I guess it must be getting here, just very weakly?

There were issues about a decade ago, reported by a then-regular on this site, where KDKA 1020's HD from Pittsburgh was interfering with WBZ 1030's analog in Boston, and vice-versa. WBZ was also interfering with his own station in the Rochester NY area on 1040.

I also was able to hear KNX 1070's HD wipe out my local (Phoenix) KDUS 1060, even when KNX's analog was inaudible or fading in and out. I didn't have an HD radio at the time, so I had no way of decoding anything.

 

[rbc]

There were issues about a decade ago, reported by a then-regular on this site, where KDKA 1020's HD from Pittsburgh was interfering with WBZ 1030's analog in Boston, and vice-versa. WBZ was also interfering with his own station in the Rochester NY area on 1040.

I also was able to hear KNX 1070's HD wipe out my local (Phoenix) KDUS 1060, even when KNX's analog was inaudible or fading in and out. I didn't have an HD radio at the time, so I had no way of decoding anything.

That's why the all-digital will be better eventually. Stations will only use a 20 kHz channel instead of 30 kHz. Less interference.

 

[bulwnkl]

Apparently I was _way_ off in my understanding of how far the HD signal (in a hybrid environment) could potentially be detected. There’s a local AM station here which has an HD signal but that I can’t ever decode unless I’m practically at the transmitter. So that combined with a couple dismissive comments I’d seen somewhere made me think that it should be impossible for me to even detect KSL’s HD signal. Apparently that’s not so!

On a note related to interference: I’ve had major difficulty getting much on AM (GE Superadio) since I moved back to AZ several years ago. Things improve at night, but there’s still major interference from somewhere. I’m not claiming it’s HD interference. I think in my case it’s something electrical around the area (can a solar array or an A/C unit or LED light bulbs mess up AM reception?), but in any event AM is not nearly as usable for me as it was in the very rural area where I grew up. If all-digital AM would help this kind of issue significantly, then maybe I’m willing to have to replace my radios.

 

[KeithE4]

On a note related to interference: I’ve had major difficulty getting much on AM (GE Superadio) since I moved back to AZ several years ago. Things improve at night, but there’s still major interference from somewhere. I’m not claiming it’s HD interference. I think in my case it’s something electrical around the area (can a solar array or an A/C unit or LED light bulbs mess up AM reception?), but in any event AM is not nearly as usable for me as it was in the very rural area where I grew up. If all-digital AM would help this kind of issue significantly, then maybe I’m willing to have to replace my radios.

Try moving your radio outside, about 10 feet from the house. Then see what happens. If your reception improves, then you might be in the same boat I'm in: Stucco house with lots of noise-making devices inside. The chicken wire holding up the stucco is good for 20-40 dB of attenuation, depending on the frequency, from AM thru WiFi. But if you're in the Phoenix area, there won't be much local AM at night to begin with, other than KFYI/550 and KTAR/620. They're the only stations with even close to full-market coverage, and KFYI is weak where I live in NE Mesa, even with the radio outside.

 

[bulwnkl]

If there wasn't a sand storm at my house just now, I'd try going outside. (-: I'll give it a shot later, if things calm down. Thanks for the suggestion.

I've wondered whether the chicken wire would be a problem. I've also wondered whether the metal foil layer on the underside of the roof would inhibit an (FM) antenna up there. I have a TV antenna outside pointed at South Mountain, but it may have an FM trap on it(? I'll have to look it up again), and anyway the distribution system in the house is 'used up' in terms of antenna cabling.

 

[bulwnkl]

Interference disappears almost the instant I leave the house. It sounds like a major electrical 'thing,' which I've discovered covers pretty much the whole lower half of the AM band. Perhaps someone wired in a little AC juice to the chicken wire? LOL!

 

[KeithE4]

Interference disappears almost the instant I leave the house. It sounds like a major electrical 'thing,' which I've discovered covers pretty much the whole lower half of the AM band. Perhaps someone wired in a little AC juice to the chicken wire? LOL!

The chicken wire acts similar to a faraday cage, or a screen room that you might have at work if you are employed at an electronics manufacting/design company. If anything, the 20-40 dB attenuation is a two-way street. It keeps the outside signals out, but it also keep the indoor noise in.

You will have to use outdoor antennas to get any kind of reception, though. HOA willing, of course.

 

[Kelly A]

can a solar array or an A/C unit or LED light bulbs mess up AM reception?

Answer: Yes and definitely yes. LED bulbs spew a broadband noise that even affects FM reception. Solar farms convert the DC voltage from the solar panel power regulators for storage in batteries. The solar regulators/battery chargers make a fair share of noise. What really makes the noise is when the solar farm takes the stored, or direct DC and convert that to AC. The giant DC/AC inverters generate a lot of switching noise that greatly affects the AM and SW band.

 

[boombox4]

Could be anything. Router power supply, switching power supplies for computers and other devices. A lot of stuff puts out RFI.

LED bulbs can, depending on brand, and how close the radio is to the LED bulb. My LED bulbs are mostly RFI-free -- the radio only picks up the hash (weakly) when it's within a foot or so of the bulb. YMMV.

 

[bulwnkl]

A follow-up on the interference issue--

It appears that the HVAC system, and _probably_ the fan motor in particular, is the single biggest source of interference in the house generally. We frequently run just the fan for air circulation even if the A/C isn't actively cooling, so I have massive interference a great deal of the time. The motor has been replaced before, and the people who did the work were simply not competent to work on residential HVAC systems, so who knows what they put in. Still not sure what's causing the rest of it, though. I took a radio out next to the solar array's inverter, and the interference doesn't seem to increase as I approach it, so I'm thinking that's not a major contributor here. Anyway, just thought I'd follow up.

 

[kenglish]

It's generally agreed that every building has a "noise cloud" that extends about 15 feet beyond the structure. If you erect an outdoor antenna for radio, keep all of the active (unshielded) parts of the antenna and transmission line outside of that noisy zone. Some recommend bringing the transmission line underground from a feed point on the antenna, at it's far end, away from the house. Also, some people use an isolator near the point where the line comes inside, to prevent noise from riding inside on the shield of the cable.
Tons of interference sources are indoors, as well as in neighboring structures. As for your HVAC, the system may be using a variable-speed (electronic) drive motor. Check out places like Palomar Engineers for info on ferrites that can be clamped on to the wires, to lower the noise. They have some good tutorials on such things.

 

[bulwnkl]

I _wish_ it had a VFD. (-: I don't understand how the fan motor could possibly be so noisy, but the noise level drops dramatically when it shuts off. Plus, the nearer I get to the IDU (in the attic), the higher the noise level. I had initially thought the compressor was the primary source, and it may be a significant one, but I still get big noise after the compressor shuts down until the fan shuts off. <shrug>

I do believe there's a bunch of junk coming into the house from (perhaps through is the better way to put it?) the very loud transformer outside, but the transformer itself doesn't particularly interfere with radio reception until I'm right on top of it.

 

[Ai4i]

can a solar array or an A/C unit or LED light bulbs mess up AM reception?

I was just recently reading about ADSL service with data that goes up to 1104 KHz and uses unshielded twisted copper pairs that were designed for basic telephone service many decades ago.
Of course, the lower limit of KSL's HD signal begins around 40 KHz above ADSL's upper limit but those providers generate square waves which are not the cleanest of emission types.

 

[bulwnkl]

How interesting! I wonder whether the cable company's internet service generates similar interference. It doesn't use tel-co copper, obviously...

Since I'm now using a Sangean HRD-16 instead of my Superadio (my son uses it for FM in the evenings), I have much less audible noise on the AM band. The interference is still there based on inability to pull various distant stations in, especially in the lower half of the AM band, but how much of the noise gets put out through the speakers is _much_ lower with the Sangean HD portable vs. the GE Superadio.