Question about FM HD vs analog fringe coverage...

[pianoplayer88key]

I was wondering about FM HD coverage in fringe areas, and FM HD receivers...
(No, I'm not (yet) thinking about getting an FM HD radio.)

How well, with the HD power increase, does HD FM do in fringe areas? (I've heard that the power increase was supposed to replicate analog coverage, but I could well be wrong.)

For example, I can often reliably receive 103.3 KVYB (analog FM) at my location from about 212 miles southeast of their transmitter. (BTW they have no local first-adjacents plaguing them, and I don't believe they run HD (at least I've never heard them advertise it).
http://www.mediafire.com/?odd1nkieuhjok
There's several clips there - one with the PL-380 on the roof of my house from last year, one with the PL-606 on a hilltop a few hundred feet higher than my house, and a couple in my back yard with the PL-606's whip antenna stored (one with the radio sitting on the ground, and still able to receive the station!)

So, let's assume there's an FM station whose analog signal I can just barely detect (much weaker than the weakest of the KVYB clips - threshold level, but not good enough audio to identify who it is) on the Tecsun PL-390 (which I don't have). Assume there are strong first-adjacent locals on either side.

So, what portable FM HD radios consistently get reliable FM HD reception when a radio like the Tecsun PL-390 is just barely able to get threshold audio on said station's analog signal (and there are strong local first-adjacents running HD, that had HD turned off when reception on the PL-390 was checked)?

Also what about co-channel interference? With FM HD is there a way to choose which station I want to hear (even when the difference in received signal in dBu is so much that if it was an AM frequency, the weaker one would be only barely audible when the stronger one is unmodulated - maybe 30-40dB or something, idk)?

 

[spunker88]

Your Tecsun radios will give the signal on their display in dbu. I'm not sure if there is an exact dbu level needed for HD, but Ive found at around 30-35 dbu is when the signal locks in. You will probably want to be closer to 40dbu to have it stay locked in.

Radios, especially the Tecsun with its nice DSP chip will allow you to listen to analog signals long after the HD signal would be impossible to receive. One of the biggest problems with HD FM is the fact that it cannot cover the same area as the analog signal mostly due to the fact that it is only broadcast at a fraction of the power of the analog signal and requires the sideband frequencies to be clear or pretty much clear. My Tecsun PL-390 pulls in DX listenable signals down into the single digit dbu levels.

KVYB has one of the largest coverage areas for an FM station. A combination of high transmitter power and a high elevation transmitter site. It is a grandfathered FM that signed on during the early days of FM trying to cover a super large area. New stations would not be allowed to cover this much area.

 

[pianoplayer88key]

Your Tecsun radios will give the signal on their display in dbu. I'm not sure if there is an exact dbu level needed for HD, but Ive found at around 30-35 dbu is when the signal locks in. You will probably want to be closer to 40dbu to have it stay locked in.

Radios, especially the Tecsun with its nice DSP chip will allow you to listen to analog signals long after the HD signal would be impossible to receive. One of the biggest problems with HD FM is the fact that it cannot cover the same area as the analog signal mostly due to the fact that it is only broadcast at a fraction of the power of the analog signal and requires the sideband frequencies to be clear or pretty much clear.

So I guess HD isn't quite good enough to dig out a weak signal that on the Tecsun would be indicating 0 dBu if it was receivable, and had first-adjacent interference running HD that was so strong it could desense a 90+ dBu signal at the opposite end of the band on the Tecsun into oblivion?
When I first was hearing about digital radio (before I even knew IBOC existed), I had thought that digital was supposed to require less bandwidth, less transmitter power, still be 100% reliable in places where the analog signal in a best-case scenario barely even had a detectable QRSS CW carrier (and too faint to ID), and be completely undetectable on an analog only radio (and not interfere with weak co-channel signals). Guess HD has a way to go to achieve that?

My Tecsun PL-390 pulls in DX listenable signals down into the single digit dbu levels.

I've heard several signals here on my PL-380 & PL-606 that indicated 00 dBu and 00 dB S/N, yet they sounded good enough for me to understand what was on the air - not quite clear (free of noise), but strong enough so it didn't have the garbled/distorted sound that weak FM signals can have.

KVYB has one of the largest coverage areas for an FM station. A combination of high transmitter power and a high elevation transmitter site. It is a grandfathered FM that signed on during the early days of FM trying to cover a super large area. New stations would not be allowed to cover this much area.

I kind-of wish they would be allowed. I'm curious.... what power & antenna height combination might need to be used on FM (or HD FM in its current incarnation or DTV) so that it still has solid stereo on a radio inferior to a Tecsun (maybe a Coby?) at a distance where an AM on 540 kHz with 2 megawatts and a Franklin antenna would, over an entirely saltwater path, have its carrier barely detectable (but too weak for audio) with a tuned (not broadband) beverage antenna hooked up to maybe a Drake or other high-performance receiver?

 

[spunker88]

Well an ad pitch is one thing, real life testing and application is another. For HD Radio I can tell from owning the Sony XDR-F1HD, one of the best DX radios out there which also has HD, that this is just not the case.

An example for my area is Syraucse, NY WYYY 94.5 which is about 70 miles from my location in Watertown, NY. It provides a decent analog signal since it broadcasts at 100kw. But I also have a semi-local station on 94.7 thats only 5.8kw about 30 miles away. I get about a 20-25 dbu signal indoors on 94.5, in stereo and its perfectly listenable. I cannot get the HD signal to lock in reliably with this. I have used my antenna outdoors and I can get the HD signal to flash but it never locks. Outside the signal goes into the 30dbu range, and the station on 94.7 gets stronger. Its probably a combination of the fact that I have a signal on 94.7 and the fact that I am only using a pair of bunny ears that the signal won't lock. Maybe if I had a decent antenna it would work, but to me this shows that HD has its flaws still if I need a outdoor antenna to receive the same signal that comes in fine indoors, even on cheaper radios.

Part of it is the cliff effect of digital that DTV also suffers. But the nice thing about DTV is it doesn't use a sideband approach to things. DTV uses a digital only in-channel system that I really think we should experiment with on FM. The dbu levels required would be much lower and maybe it would prove to be a more reliable system. DTV was made to cover the same area as its analog signal and if channel plus ERP were kept the same it comes pretty darn close. Unfortunately most stations either moved to a weaker UHF signal or lowered their power. I would like to see how far signals like KVYB would travel if they were 100% digital with the same ERP as an analog signal. They could also experiment with using something like subcarrier audio as an analog fallback. I personally think analog FM plus RDS is a great system since you can still get all of the text goodies of HD Radio.

 

[nd2023]

I'm 60 miles away from the NYC stations and 30 miles from the Philly stations. I can get the Philly stations on my Insignia portable HD radio with dropouts, even 101.1 which I know is -14. I can get 107.5 from NYC to flash the HD light on my Insignia, but it doesn't decode. My Sony XDRF1HD and outdoor antenna can get all the HDs from Philly and all but WQXR from NYC in HD. The NYC stations are staticy in the car. I can get a few Baltimore and Connecticut stations in analog almost all the time but no HD.

Last night there was tropo and I got Star 99.9 from Connecticut in HD. 2 days ago there was E skip and I got the HD indicator to light up for a few e-skip stations. I even got a few seconds of HD audio from XL106.7 in Orlando.