FM IBOC power increase - question

[dxer2_2000]

Hi guys

no doubt you are all apprehensive about the proposed FM IBOC power increase. With this stronger digital power + with all the analogue signals, will this produce a greater mixing product & harmonics problem?

I wonder if harmonics of IBOC carriers would even decode :eek:

Geoff

[K4NBF]

I'm sure one of our more technically inclined posters will probably have a better thought out answer than me, but whatever...

I'm not sure about harmonics, but a lot of people are concerned that the analog signal of an HD station will be impacted by its own IBOC sidebands. I already observed this issue at my prior QTH - on my lesser quality radios, like cheap portables or clock radios, I noticed an change in background noise levels when stations would have outages on their IBOC signals. This was probably a unique situation at current power levels, because of my prior location in a hilly area.

I'm personally not worried about the power increase. I think most stations will not invest in the increase, and I firmly believe HD has peaked, and will slowly self-destruct in the years to come.

[antennanut]

I hope HD has peaked. It is so bothersome on both AM and FM. Clear Channel seems to be the biggest supporter - if IBOC falls out of favor with CC, it would be a nice dagger.

[cd637299]

I'd love to have IBOC go away for good....but as long as iBiquity is trying its last gasp here with an increase in power, my question will be----

What can I (as a DXer) expect on the FM dial come Monday? Will this increase make the 2nd-adjacents more of a pain to hear? Will 1st adjacents be even tougher to poke thru the already-difficult IBOC signal?

Inquiring minds....

cd

[w9wi]

no doubt you are all apprehensive about the proposed FM IBOC power increase. With this stronger digital power + with all the analogue signals, will this produce a greater mixing product & harmonics problem?

I wonder if harmonics of IBOC carriers would even decode :eek:


On the one hand, anything that increases the amount of power being radiated will increase the number/strength of mixing products.

Barring other changes, harmonic power will also increase. (however, that increase will IMHO be negligible as *compared to the total analog+digital power* the power increase is pretty small) In any case, harmonics fall into Band III (VHF-High) TV channels. 176-216MHz, channels 7-13 in the USA.

I've heard IBOC self-interference on AM. It's becoming increasingly difficult to find as IBOC-AM is gradually disappearing! (we only ever had two such stations in Nashville & one has dropped it) I've not heard it on FM but as Bryce suggests I think it's quite receiver-dependent. To the extent that it exists on FM it will get worse.

I do *not* expect IBOC-FM to go away anytime soon. It's proving useful in a few niches -- around here, public radio is pushing it and for good reason, it relieves the conflicts over having three different popular genres of programming and only one frequency. Another station is using it to feed a translator, bringing Nashville a format I'm actually rather surprised no regular FM station has tried.

But I don't think implementation of the increase will be immediately universal. I don't see a business plan for IBOC at most commercial stations. It's probably not practical to do with high-level combining. Which means chances are, stations implementing the increase will have replaced their analog transmitters with new units. Given the poor economy, we're not going to see stations running out to replace their transmitters.

(that said, the economy is beginning to show signs of life -- and as our GM told us at the TV station last week, broadcasting is a leading indicator. In a recession, our bottom line goes away before it does at other industries -- but it also comes back before it does at other industries.)

Whether this will cause problems for 2nd adjacents depends on your radio. I would suggest for most decent DX radios, 2nd-adjacents are not an issue. 1st-adjacents, yes, it's going to be harder -- but again, that's assuming stations actually implement it.

I should say, I have my doubts many stations are going to be sending an engineer to the transmitter Monday morning to throw the switch on the increase. It's going to be a trickle rather than a flood.

[k6sti]

I think Doug's right about the digital power increase coming as a trickle. I haven't looked for a couple weeks, but the last time I scanned the FM band with my spectrum analyzer I found no signal with digital sideband levels above the usual -20 dBc, except for one station that has been experimenting with higher levels for years on a special test basis. Any station has been allowed to increase its digital power for the last month by asking for special authorization, which is immediately given. I read that a number of stations across the country have done this.

Some stations will be able to increase the digital power level immediately due to existing transmitter headroom. One local station I know will be doing that. But I think these stations are in the minority.

Interference 400 kHz away should be negligible even with a digital power boost (maybe not 10 dB though) unless the transmitter does not meet the power rolloff mask spec. One local station doesn't and even at -20 dBc I can hear some interference on a station 400 kHz away. But I think well-engineered stations should be OK.

The digital sidebands extend 198 kHz from channel center. This covers one sideband of each adjacent signal. It would be worth trying an analog receiver with a narrow IF filter, tuning off to the remaining sideband to see if you can recover anything useful. The audio will sound awful with one sideband attenuated, but I'll bet it will be intelligible enough to ID a DX station.

The best way to reduce digital interference is to carefully aim your antenna. If you can drop a pattern null on the interfering signal, you'll hear a great improvement even if doing so drops the desired signal.

Brian

[pjdyer]

Lacking a spectrum analyzer (in this hometown of Clear Channel) I can't tell who has/will increase their IBOC levels. Every now and then one (or several) show up for a few hours, days (sometimes weeks) without it giving me temporary false hope. In early 2009 I finally got a Bolin Phase Box in an effort to combat those local IBOC sidebands. In some instances it works wonders, but not so well with the gang of 100-kws 9 mi w.n.w. of me. It's most effective for tropo events when nulling/peaking with its two knobs is far easier with the slow QSB vs. Es. With the limited dynamic range "s-meter" of the XDR-F1HD it can be very frustrating in getting a null if that null is well above its max 3 bars and the sweet spot is only maybe 5-deg wide on the Bolin Box knobs :(

73, Pat - WA5IYX

[dlp85x]

Although I don't want this to happen, I wonder what FM DXing would be like if there was a digital FM transition much like we had for TV last year. Let's use 95.5 WPGC Morningside, MD (a local of mine that runs HD) as an example. Let's say with this transition that their 95.3 and 95.7 HD sidebands are gone, as well as the analog 95.5 signal. Instead, they run IBOC at full power (50kw) on 95.5 with no sidebands. Would it reach the same audience as their (current) analog counterpart if the HD was at the same wattage? Would there be any interference on 95.3 and 95.7 on radios like the Sony XDR-F1HD? Would this bring back the capability of DXing distant stations on adjacent frequencies (also with HD if tuned in)?

Granted, this scenario would wipe out a lot of Tr and Es (especially muddy signals), so I know it would be very detrimental to DXing, but I'm just curious as to how this would all factor into DXing, as I am sure iBiquity probably wants to have a similar FM 'transition' like we had to TV--that is if they had their way.

[k6sti]

David, the sidebands remain and increase 18.5 dB in power.

Brian

[spunker88]

Although I don't want this to happen, I wonder what FM DXing would be like if there was a digital FM transition much like we had for TV last year. Let's use 95.5 WPGC Morningside, MD (a local of mine that runs HD) as an example. Let's say with this transition that their 95.3 and 95.7 HD sidebands are gone, as well as the analog 95.5 signal. Instead, they run IBOC at full power (50kw) on 95.5 with no sidebands. Would it reach the same audience as their (current) analog counterpart if the HD was at the same wattage? Would there be any interference on 95.3 and 95.7 on radios like the Sony XDR-F1HD? Would this bring back the capability of DXing distant stations on adjacent frequencies (also with HD if tuned in)?

Granted, this scenario would wipe out a lot of Tr and Es (especially muddy signals), so I know it would be very detrimental to DXing, but I'm just curious as to how this would all factor into DXing, as I am sure iBiquity probably wants to have a similar FM 'transition' like we had to TV--that is if they had their way.

I imagine there will be a digital transition on FM eventually, mostly as technology improves and gets cheaper. Analog FM radios can be built very cheaply, demand little power, and are reliable. HD radios will have to be able to provide the same experience in order for them to be considered a replacement for FM. Without analog FM, in theory you would not have to run sidebands, and would be able to broadcast HD on the channel itself formerly used for analog.

[dlp85x]

David, the sidebands remain and increase 18.5 dB in power.

Brian

Pardon me for the confusion, but you mentioned that the sidebands remain--does this mean that IBOC must operate with two sidebands (and not just one IBOC digital signal on one frequency)? I think you mean if the station ups their IBOC power to 100% and keeps the analog on-air, or if they turn the analog off but keep the two sidebands at 100%.


I imagine there will be a digital transition on FM eventually, mostly as technology improves and gets cheaper. Analog FM radios can be built very cheaply, demand little power, and are reliable. HD radios will have to be able to provide the same experience in order for them to be considered a replacement for FM. Without analog FM, in theory you would not have to run sidebands, and would be able to broadcast HD on the channel itself formerly used for analog.

Yeah, that is what I was getting at...a scenario that mirrors the digital TV transition, but for FM. In theory, one could DX 95.3 and 95.7 without ‘HD hash’ from a single-frequency IBOC signal on 95.5 unless they are very close to the xmtr (same as now with analog.) So, in other words, the band would be identical to how it was before IBOC was invented after such a transition, but all signals would be digital. This, of course, assumes that a 50kw IBOC signal reaches as far as a 50kw analog signal. I really doubt that would happen, but the signal would get out much further than the weak ones do now.

Imagine an intense Es opening after such a transition where every FM signal that (in analog mode would have a somewhat fairly clear signal) comes in with HD and call letters on the screen—not just the few signals whose low-power IBOC sidebands comes in among very strong analog signals like now. I don’t mean to sound like I want this all to happen—I like IBOC for the instant ID and the ability to log stations over strong locals that I’d otherwise not get—but it is just interesting to consider what it would be like in this scenario. Sorry for going slightly off-topic!

[k6sti]

The HD Radio standard includes the current hybrid analog/digital system and an all-digital system. The all-digital system retains the current digital sidebands but increases their power 18.5 dB.

For details, see the attached iBiquity technical document.

Brian

[dlp85x]

The HD Radio standard includes the current hybrid analog/digital system and an all-digital system. The all-digital system retains the current digital sidebands but increases their power 18.5 dB.

For details, see the attached iBiquity technical document.

Brian

Thanks for the explanation. So, apparently the sidebands have to be there regardless of if an analog signal is present or not. :( I had hopes that in 10-15 years (or whenever a transition happens) that they'd just take one sideband, re-tune it to the original analog frequency, and call it a day!

[spunker88]

Yeah, that is what I was getting at...a scenario that mirrors the digital TV transition, but for FM. In theory, one could DX 95.3 and 95.7 without ‘HD hash’ from a single-frequency IBOC signal on 95.5 unless they are very close to the xmtr (same as now with analog.) So, in other words, the band would be identical to how it was before IBOC was invented after such a transition, but all signals would be digital. This, of course, assumes that a 50kw IBOC signal reaches as far as a 50kw analog signal. I really doubt that would happen, but the signal would get out much further than the weak ones do now.

Imagine an intense Es opening after such a transition where every FM signal that (in analog mode would have a somewhat fairly clear signal) comes in with HD and call letters on the screen—not just the few signals whose low-power IBOC sidebands comes in among very strong analog signals like now. I don’t mean to sound like I want this all to happen—I like IBOC for the instant ID and the ability to log stations over strong locals that I’d otherwise not get—but it is just interesting to consider what it would be like in this scenario. Sorry for going slightly off-topic!

It would have pros and cons for Dxing just like digital has for TV. With DTV, having PSIP's gives you an instant ID. But also digital signals have the cliff effect and it has to be a pretty clean signal without interference in order to render. During ES its common to have two analog FM signals fighting on a single frequency. With digital only, you'd probably hear a blip of audio every now and then, and would have to rely upon the RDS.

Idealy, digital FM stations should be receivable anywhere an analog FM station can sustain a good stereo signal. I have analog FM 100kw stations from 70-80 miles away that i can get in a good stereo signal, but I doubt current HD would work at that distance.

[AB3IU]

I'm not sure about harmonics, but a lot of people are concerned that the analog signal of an HD station will be impacted by its own IBOC sidebands. I already observed this issue at my prior QTH - on my lesser quality radios, like cheap portables or clock radios, I noticed an change in background noise levels when stations would have outages on their IBOC signals.

Local station WAMU has increased their HD power, and I've noticed lately that my analog reception is a lot more fiddly with the cheap-ish radio I use to listen to it at work. I used to be able to walk around my office without any fading, but now depending on where I'm sitting it goes out a bit. I seem to hear more white noise in the background when it's properly tuned, too, but that may just be in my head.

I sent them a note about it when they were asking for listener reception reports for the power increase and never heard back. What I don't know is when exactly they did this, so it may very well just be a result of some other change in my office or building.

[k6sti]

Idealy, digital FM stations should be receivable anywhere an analog FM station can sustain a good stereo signal. I have analog FM 100kw stations from 70-80 miles away that i can get in a good stereo signal, but I doubt current HD would work at that distance.

I reliably receive HD signals from stations 90 miles away that run less than 10 kW.

For both the Sony XDR-F1HD and the Sangean HDT-1X, I have measured the signal level required for reliable HD lock as 29 dBf. This level is about 7 dB below the signal required by a good analog tuner for 50 dB of stereo quieting. This is for digital sidebands at -20 dBc. For the new -14 dBc sideband level, 23 dBf would be required. For an all-digital signal with sidebands 18.5 dB higher than -20 dBc, 10.5 dBf would be needed. This level is 4-7 dB below the typical 50 dB monophonic quieting point of a good tuner.

Interference on one adjacent channel increases the required signal level 3 dB. Strong interference on both channels makes HD reception impossible.

Brian

[k6sti]

I seem to hear more white noise in the background when it's properly tuned, too, but that may just be in my head.

It's not. See this:

http://ham-radio.com/k6sti/hdrsn.htm

Brian