An interesting "HD" post on the Phila. board

[radioskeptic]

"SignalSeeker" from Lancaster, PA says he can get Philadelphia FM IBOC on his new Sangean HDT-1 tuner. (Here's a link: http://www.radio-info.com/smf/index.php/topic,65824.0.html)

As far as receiving the Philly stations, I receive all them them in HD with the standard dipole supplied with the HDT-1. The only one that is hard to get is WDAS. I could barely get it, mainly because of a strong country station near me, WIOV at 105.1, coming from Ephrata, Pa. The selectivity of the Sangean is phenomenal. When I place it on seek, or seek HD it picks out WDAS at 105.3. A second later it displays the HD symbol and then it locks in. It surprised me when the tuner did this. I usually had to tweak any of my other tuners manually to get DAS.

Both of these are Class B stations. SignalSeeker says he's 60 miles from Philadelphia, and the map shows Ephrata is barely 20 miles from Lancaster. According to the contour maps on radio-locator.com, Lancaster is barely within the 40 dBu contour for WDAS-FM, but it looks like it would be well within the 70 dBu contour for WIOV. Now that alone is a difference of 30 dB; but when you add the 23-dB difference in level between a Hi-Deaf signal and its host analog, that makes a total of 63 dB, give or take a little for atmospheric conditions.

SignalSeeker claims he gets most Philly Hi-Deaf signals on the dipole supplied with the tuner, but it's not clear whether he means he has to resort to his rooftop antenna for WDAS-FM.

Even so, WDAS-FM's lower Hi-Deaf signal is actually a co-channel signal for WIOV-FM (being between 105.102 and 105.171). So what kind of antenna could possibly provide the >60dB rejection at the side that he would need to get that Philly Hi-Deaf signal?

I'd like to see some of the regulars from this board jumping into the fray on this one.

 

[HD_Ready]

what's so unusuall about that?!?!?

I live 40 miles from a Class A with HD on 88.9 and 20 miles from a Class B with HD on 89.1, no problems picking either of them up in my driveway or on my BA receptor (long diapole)

 

[PhilJSmith67]

> 60dB rejection is unnecessary, unless there is a relatively strong first-adjacent both above and below 105.3 WDAS-FM. I get a lock on several HD signals from stations that are hardly 20dB above their first-adjacent analogs. This is using rabbit-ears (not as efficient as a dipole) with a Sangean HDR-1 tuner. I can still get the weaker analogs in some cases, too, but it's tougher through the IBOC sidebands.

 

[SUPERCASTER]

> 60dB rejection is unnecessary, unless there is a relatively strong first-adjacent both above and below 105.3 WDAS-FM. I get a lock on several HD signals from stations that are hardly 20dB above their first-adjacent analogs. This is using rabbit-ears (not as efficient as a dipole) with a Sangean HDR-1 tuner. I can still get the weaker analogs in some cases, too, but it's tougher through the IBOC sidebands.

Yes, HD buzz really trashes the neighborhood.

 

[PhilJSmith67]

It certainly makes it tougher. At home, at least I have a chance to orient the antenna to capture the weaker analog stations. In the car, it's a different story. The first-adjacents get rapidly battered, like an extreme form of picket-fencing. One of the Chicago stations had its HD signal off for several hours about a month ago, and previously-listenable stations on both of its first-adjacents easily came through. One came through with RDS info. The HD signal has since returned, and these stations are effectively unlistenable in the car again.

Sorry; I realize that wasn't the point of this thread... :-\

 

[radioskeptic]

A reply to Philip J. Smith:

Your Reply # 4 was very much to the point of this thread. You said you could orient your antenna to get weaker first-adjacents – but how much weaker?

Go to www.radio-locator.com, look at the coverage maps for the stations in question, and tell us their approximate predicted field strengths at your location (and if you don’t want to reveal your location, list the stations as Station A, Station B, etc.).

Now let me answer what you said in Reply # 2.

Just re-read my post at the top of this thread. “SignalSeeker” is trying to get a distant “HD” signal in the presence of a local first-adjacent. Both are full-powered Class B’s, and the difference between the predicted levels of their analog signals at his location is probably in the 30-33 dB range. Add another 23 dB for the difference in level between that “HD” and its (already weak, distant) host analog, and you have a total difference of >60dB between the analog of the local signal on 105.1 and the (de facto co-channel) lower digital side channel of the distant station whose analog is centered at 105.3!

(Note: I said “lower digital side channel,” and not “lower digital sideband,” because the IBUZZ signals are NOT an integral part of the host analog signal – or for that matter, of each other. More important, they’re not symmetrical. An FM signal has constant amplitude; but when it’s combined with another signal or signals, there will be amplitude variations. That’s why installation of IBUZZ often requires either a new transmitter or a couple of additional low-powered transmitters and a combing network to feed all three signals to the antenna – because the high-efficiency Class C finals in many transmitters can’t accurately amplify the resulting amplitude variations in the three signals. Contrast this with FMeXtra, where an analog SCA is replaced by a digital one, which modulates the frequency of the main carrier – producing no analog variations, and thus offering combating compatibility with existing transmitters – and staying with the conventional limits of the channel to boot! No interference with first-adjacents in your car!)

 

[PhilJSmith67]

My apologies... I had the analog vs. HD signal on first adjacents "flipped" in my head when I answered! :-[

 

[Mike Walker]

Anyone with an HD radio knows that if the HD station is clear of a strong first adjacent on ONE side, then you'll almost certainly get HD.

And I defy ANYONE to give me recorded evidence of FM HD covering up first adjacent analog signals. I've actually had the experience of getting a station to cycle it's HD on and off while I listened to first adjacent stations. No difference. NONE.

 

[PhilJSmith67]

Oh believe me, I have stations 35 miles away running HD from Chicago that totally cover up first-adjacent stations 40-45 miles away that were very much listenable, in stereo and with RDS, until the IBOC signals arrived.

It's especially noticeable in the car (and I have a radio with good selectivity, too), and the rumble/buzz sound of the OFDM data is there. It's audible to the point that I could tell which Chicago stations were running HD long, long before I owned an HD Radio receiver. In the car, these previously listenable stations now have rapid picket-fencing characteristics while driving, making them completely unlistenable. When one of the offending stations recently had their IBOC signal turned off (106.3 WSRB Lansing), and 106.5 WXNU St. Anne became listenable in the car for a full 10 miles farther north than with the IBOC signal on. A very similar situation existed when WLUP Chicago had their IBOC signal turned off; first-adjacents on both sides of WLUP were back.

The problem with recording it? Well, I can't have these stations turn off their HD Radio signals just for my own little recording experiment, and unless I were to encode the recording at 320kbps, it wouldn't have enough clarity to tell the difference between vacant-channel thermal noise or OFDM chatter.