I always love it when someone tells me I'm wrong and then goes on to prove exactly what I just said. Unfortunately, the amount of righteous self-importance shown by some people here is indicative of the same trait throughout the industry. Makes one wonder why the people who actually know what they're doing bother at all.
-
Get involved.
We want your input!
Apply for Membership and join the conversations about everything related to broadcasting.
After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
If you use a disposable or false email address, your registration will be rejected.
After your membership is approved, please take a minute to tell us a little bit about yourself.
https://www.radiodiscussions.com/forums/introduce-yourself.1088/
Thanks in advance and have fun!
RadioDiscussions Administrators
Some clear thinking on IBOC: Skotdal: AM Band Needs Drastic Change
- Thread starter KB1OKL
- Start date
Translation: you were wrong and you are now behaving like a cat and trying to cover up your mistake.
It's also amusing when someone intentionally takes away exactly the opposite of what I've said. That's when I know my point has been proven and they just don't want to admit it.
But your point has not been made. The analog TPO and ERP of a station does not change whether HD is on or off.
Hey Josh, I realize I'm late to this discussion, but the easy way to think about analog & HD signals is to think of them as two completely different radio stations, on different frequencies. An FM station on 98.1 MHz uses 98.0-98.2 MHz for the analog signal and 97.9-98.0 plus 98.2-98.3 for the digital carriers. There's a pretty good diagram depicting that on page 34 of this document:
http://www.nrscstandards.org/SG/NRSC-5-C/NRSC-5-C.pdf
That doc is the most comprehensive data I've found on HD radio - both AM & FM. There ARE situations where those digital carriers can impede analog reception, but it's not due to a decrease in the analog power.
Dave B.
R
rbrucecarter5
Guest
Thank you! Finally someone else is saying what I've been saying all along! To elaborate - spectrum analyzers are NOT radios! They don't show a decrease in analog power. But radios, which have AGC circuitry so they can accommodate a large dynamic range in received signals, get confused by HD sidebands and ramp the gain down, effectively killing sensitivity. I've verified this by breaking the AGC loop in radios for both AM and FM, and patching in a control voltage. It because crystal clear that the radio still had tons of gain for weak signals, but the control voltage I was sending to the radio to restore its sensitivity was very different from what the radio was sending. As a control, I checked on analog only signals of similar strength, and sure enough the AGC voltage was different. The only variable was HD. I even added a switch, and it was gain way down for an HD station, gain up for analog only. I only wish I had the time to do it during a local station's outage a couple of weeks ago.
Short of getting a station to switch HD on and off for me while I experiment, I can't think of a more carefully crafted experiment. I can state with complete confidence that HD severely affects receiver sensitive on both AM and FM bands - an unanticipated consequence of the sidebands. Especially when the radio has wide IF ceramic filters installed, as most do these days, especially AM. Wide filters receive that extra sideband energy, interpret it as more station power, and the AGC circuit scales back the gain. This is not difficult to understand, there are a lot of references on AGC circuits for both AM and FM conveniently on the web. Different manufacturers implement them differently, some better than others - Sony radios used to be notorious have bad AGC on FM resulting in images all over the dial from strong stations. Radio Shack gets it wrong on AM radios. C Crane gets it wrong on AM in the CC-EP on the upper half of the band. GE and RCA generally get it right, and Sony finally started getting it right.
So what if a station's range goes down by 60 miles - the local stations don't care about either Huntsville or Centerville. But the same thing that affects range also affects building penetration and stations DO care about that, whether it is an AM trying to penetrate a house full of CFL bulbs and home networking, or an FM trying to penetrate a steel frame office park. The result of HD is the same. Less listeners because fewer people can hear the signal. Fewer listeners = less ratings and there you have it. HD hurting a station's bottom line.
I really like HD! It gives me format choices that aren't available on analog like Christian rock, smooth jazz, oidies, indie rock, eclectic, 80's and 90's. But as nice as these are, they are provided by stations at the expense of building penetration, and therefore it is a bad business decision for an FM to provide these HD-2 formats for relatively few listeners. They need to blast as much signal to listeners as they can, not fool with a defective technology the consumer simply does not want!
That Kool-Aid sure tastes good, doesn't it?
Bruce, what about an A/B comparison on an AM station that runs HD during the day and not at night? A couple weeks ago I had the chance to record it, but other activities prevented it. I was at my granddma's house about 4.5 miles west of KDIS's transmitter. I actually did try once, but think I missed it by a few seconds. I would have been using a Sony SRF-42 (for its wideband AM Stereo which wreaks havoc with HD in the analog audio), and the Tecsun PL-606 or PL-398bt (whose narrowband DSP filtering would eliminate the sidebands, although the latter has a broken internal antenna.)
And I was thinking - instead of HD to get multiple channels, why couldn't our radios have better selectivity across the board, so we could fit more analog stations in a given area? Something interesting I've noticed - I have 2 local 1st-adjacents on 1030 and 1040 of comparable strength that my radios separate just fine (except my cheapest Coby and maybe one other), yet a local on 1170 swamps one out of L.A. on 1150 that's about 65-70 dB weaker. A local on 1130 does the same for 1110 Disney, just not as big of a difference, and my SRF-59 and SR3 can still pull it in well enough to hear it. Right before sunset when the skywave for 1110 is strong, before it switches to night pattern (dropping considerably in strength here), their HD will sometimes step on my local on 1090 (which is directional - I'm off the side, and they're only a few dB stronger than 1070 KNX).
And I was thinking - instead of HD to get multiple channels, why couldn't our radios have better selectivity across the board, so we could fit more analog stations in a given area? Something interesting I've noticed - I have 2 local 1st-adjacents on 1030 and 1040 of comparable strength that my radios separate just fine (except my cheapest Coby and maybe one other), yet a local on 1170 swamps one out of L.A. on 1150 that's about 65-70 dB weaker. A local on 1130 does the same for 1110 Disney, just not as big of a difference, and my SRF-59 and SR3 can still pull it in well enough to hear it. Right before sunset when the skywave for 1110 is strong, before it switches to night pattern (dropping considerably in strength here), their HD will sometimes step on my local on 1090 (which is directional - I'm off the side, and they're only a few dB stronger than 1070 KNX).
But didn't you claim in an earlier post, that you arrived at your result of lower building penetration for stations running IBOC/HD carriers through the use of an Agilent piece of test equipment? Which would be either a spectrum analyzer or network analyzer. So which is it, certain radios used in a test, or a test gear? I would argue that use of certain radios in such a test are not scientific at all, but actually subjective and random. Are you testing in a steel structure with a hill line of site between the testing location and the transmitter site? What is the distance? What is the station ERP in that direction? What is the antenna gain used with the radio(s) being tested? In other words, I'd be interested in the methodology of your test, because what you've claimed so far, doesn't jibe with anything that is related to the loss of field strength or penetration into a structure, and appear are not done using any industry standards. Your claims are simply too broad and, with all due respect, don't make any sense. The fact is, if a station is operating at their licensed ERP without a damaged transmit antenna, the analog coverage will not be degraded with the HD carriers on or not.
Again, if the analog field strength isn't being affected because the digital carriers are fed from a separate source, then how would you ever make some wild claim that a station would lose some distance like 60 miles by running IBOC/HD carriers? I've never heard of one single example that you claim, because losing 60 miles of coverage would easily degrade all the way well into to the 70dBu contour of a station, even a Class C. No station owner or group would tolerate that.
I think what Mr. Carter is trying to say is that the reception and not the transmission is at fault. Re-reading his post, he seems to think that analog receivers detect the digital sidebands and the AGC reduces the rf gain of the receiver in proportion to the digital signal, thus causing the analog signal to appear to the listener as weaker.
However, this does not pass the "management test". That's where the GM or GSM calls the engineer and says, "I was out at (insert a client's address) and the station does not sound like it used to..." As you say, no station would go for more than a day or two with a truly impaired signal without major noise coming from somewhere else in the building.
Agreed David. It's just that Bruce has made this claim on more than one occasion, yet his criteria is vague and certainly nothing I've ever experienced, let alone ever heard of. I'd like to understand more of how he's coming to the conclusion with more details of his tests.
Now I do agree that some radios, the factory radio in my 1998 Jeep Cherokee that has been relegated to hauling my dogs to the park, does have the symptom of going into stereo blend mode when an FM station is running a 93Khz subcarrier, but it doesn't lose reception sensitivity. Ironically, that same Chrysler (Visteon) radio isn't affected by stations running IBOC/HD carriers.
Now I do agree that some radios, the factory radio in my 1998 Jeep Cherokee that has been relegated to hauling my dogs to the park, does have the symptom of going into stereo blend mode when an FM station is running a 93Khz subcarrier, but it doesn't lose reception sensitivity. Ironically, that same Chrysler (Visteon) radio isn't affected by stations running IBOC/HD carriers.
Another very unsophisticated test result here. When visiting my parents -- on Boston's North Shore -- I sometimes stay overnight in the basement. As an experiment, I brought a cheap portable HD receiver with me once to see whether the HD signals from the Boston stations penetrate. Well, they all do, even the ones from the Needham transmitter farm, 21 miles away as the crow flies. The main analog signals sound fine. As these stations all came in with no problem on a conventional AM/FM portable on previous visits, I also tend to doubt Bruce's claims. But again, I don't have professional equipment, just radios and ears.
Is that Jeep radio one of the receivers that I have heard about that attempted to eliminate adjacent channel interference by reducing bandwidth? As it was loosely explained to me, if there was anything odd such as two signals in the normal bandwidth it would drop to mono and narrow the bandwidth.
The context when such radios were described to me was that of stations that exceeded +/- 75 kHz modulation as is common in a number of places where I have worked. Apparently, those radios exhibited the popping or gurgling "sawing" effect that can be heard when modulation exceeds receiver bandwidth.
I've not experienced any popping, gurgling, or sawing sounds with that radio, but there was one station in the Seattle-Tacoma market that used to run both 67 and 93Khz aural subcarriers, causing the radio to drop into what Chrysler called, 'blend-mode', which reduces the high frequency audio response and mono-summed the audio, yet the stereo pilot indicator was still on. I E-mailed the factory and asked whether there was a feature that reduced adjacent channel interference by dropping the radio into mono. A very nice engineer from Visteon contacted me and confirmed that a processor algorithm did exactly what I experienced to eliminate adjacent channel noise. He said they had never considered the affect of subcarriers. Of course that was before HD radio came along and when testing of one of the first IBOC stations in Seattle began, I was sure the radio would have a fit. Surprisingly, the radio doesn't seem to care. I've heard that some older Blaupunkt radios in 90's vintage Volvo's with European IF sections, had a similar problem with 93Khz subcarriers.
Once again, the proof would be in the pudding... Er, ratings. If stations are losing coverage on the fringes or in buildings, it stands to reason that ratings would decline in some fashion.
No only does that not seem to be the case but I don't think any AM stations running HD have connected lost ratings to the digital broadcasting, even though it's painfully crappy sounding on many radios.
No only does that not seem to be the case but I don't think any AM stations running HD have connected lost ratings to the digital broadcasting, even though it's painfully crappy sounding on many radios.
Last edited:
Exactly. One great example is WBZ Boston.
Yes agreed WBZ sounds like krap since IBOC. The few times they have used their non IBOC backup transmitter they have sounded twice as good. And the backup is only 10 kW (I believe) compared to their main which is 50kW.
The better the selectivity the worse the high frequency response.
David, does that mean 40% of Americans tune into AM at some point during a week? Or do I have that wrong.
- Status