Is there anywhere to find a list of stations running IBOC at −10dBc?
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Who is running −10dBc?
- Thread starter JerseyShor
- Start date
Anybody? How about some grandfathered superpower FM's - that would be unreal how far that HD (might?) reach? Not to mention blow 10KW of noise on the first 2 adjacents!
WBCT isn't allowed to go to -10dBc referenced to its actual grandfathered analog facilities (320kW/238m HAAT). Nonetheless, its "-20dBc" grandfathered IBOC runs at -8dBc referenced to normal Class B maximum facilities (50kW/150m). It's quite an interference generator.
Nick said:
What I think "local oscillator" was trying to say -- and what is the FCC regulation -- is that the IBOC digital power for a grandfathered station is calculated relative to the class maximum, not the grandfathered superpower. Q94 would be limited to 10,000 HD watts, because the -10dBc would be calculated relative to the 100kw class maximum, not the 200kw grandfathered power.
WBCT's antenna is higher than 150m, so its class maximum (against which its HD power would be calculated) is less than 50kw.
Actually, what I was trying to say is that WBCT isn't allowed to increase to -10dBc due to its grandfathered status, but it is allowed to run its IBOC at -20dBc referenced to its grandfathered facilities. -20dBc referenced to 320kW/238m is the same as -8dBc referenced to 50kW/150m. WBCT's facilities exceed maximum Class B facilities by 12 dB. A non-grandfathered Class B with 238m HAAT would need to reduce power to 20kW; WBCT runs 320kW.
I am not aware of a list of stations that are running at -10 db. However, I believe there are probably less than a dozen. I occasionally check the FCC site to see who converted to digital and who increased their power. Based on my recollection, a station in Oregon and Ohio, and a few stations in Utah have raised the power to -10db. I am guessing that 100 or so stations are running at -14 db. I am not aware of any new AM conversions lately and believe AM IBOC is withering on the vine, while the FM system is gaining traction - albeit at a snails pace.
As far as I know, there's not a comprehensive list of stations running at -10 dBc, but anyone planning to operate at this level is supposed to request special authority from the FCC. For example, see the most recent STA application listed here for WJAZ:
http://licensing.fcc.gov/cgi-bin/ws.exe/prod/cdbs/pubacc/prod/app_list.pl?Facility_id=65184
If you open this application form and review the attached engineering statement, you'll find a contour study showing that the 49.5 dBu contour of WJAZ protects all first-adjacent stations. Unfortunately, superpower facilities like WBCT and KRTH aren't required to make a similar showing at the standard -20 dBc level, and that's why some serious interference problems have developed.
http://licensing.fcc.gov/cgi-bin/ws.exe/prod/cdbs/pubacc/prod/app_list.pl?Facility_id=65184
If you open this application form and review the attached engineering statement, you'll find a contour study showing that the 49.5 dBu contour of WJAZ protects all first-adjacent stations. Unfortunately, superpower facilities like WBCT and KRTH aren't required to make a similar showing at the standard -20 dBc level, and that's why some serious interference problems have developed.
Somebody tried to explain to me that WBCT was still grandfathered at 500kw. It was the way they reconfigured the antenna for vertical and horizontal polorization that it figures to 320kw instead of 500kw. But the ERP was the same.spunker88 said:
Can somebody help me with this?
I assume if the analogue were removed they would be a regular "B" in digital.
Jeff in Sa-ra-so-ta!
badjef said:
Just guessing here -- but I suspect the expense of operation with full circular polarization at 500 kW was determined to be cost prohibitive. The original WJEF (later WBCT) facility was horizontal only, so the number of antenna bays or the TPO would have needed to be doubled to maintain 500 kW ERP. A bigger antenna would have required more vertical space on the tower (and additional structural capacity), while a 2 X increase in TPO would have required larger diameter transmission line, also adding to weight and windload -- not to mention a much bigger power bill. So the 320 kW CP operation was a 1.9 dB compromise that allowed the owner to retain "bragging rights".
For a photo of the 50 kW RCA transmitter installed at WJEF in 1961, see Page 6 of this edition of RCA Broadcast News (the PAs were modified low-band VHF TV amplifiers):
http://www.americanradiohistory.com/Archive-RCA-Broadcast-News/RCA-BC-112-1961-Dec.pdf
I wonder which FM station currently holds the worldwide ERP record -- does anyone here know? In the late '70's, I believe it was "Radio 24" which transmitted from one of the Italian Alps towards Zurich, Switzerland with 8 megawatts in the main lobe.
badjef, WBCT is no longer grandfathered at 500 kW, but is licensed at 320 kW at 780' HAAT. Check out this link from Jeff Miller's radio history website: http://jeff560.tripod.com/fm-max.html. About halfway down there is quite a bit of info on WJEF/WJFM/WBCT and its power/licensing machinations through the years. The word going around back then was that the power reduction to 320 kW was determined by the max they could get out of stock transmitters and a CP antenna, which turned out to be the Harris twin 25's and 12-bay.
Freebird, just above the WJEF section, there is an email to Jeff about "Radio 24" and its 8 megawatt lobe. No idea who wears the crown now.
Freebird, just above the WJEF section, there is an email to Jeff about "Radio 24" and its 8 megawatt lobe. No idea who wears the crown now.
The commission has proclaimed that no grandfathered FM facility shall transmit digital sidebands in excess of the greater of 10% of what a new facility would be licensed for or 1% of their actual facility. This attempts to eventually greatly reduce the signal advantage which those stations enjoy, as only a handful of California stations have facilities more than 10db greater than currently licensed facilities 
As it should be. In fact, I would argue that the "or 1% of their actual facility" part shouldn't be allowed either. These stations have been grandfathered to operate with analog superpower ON their assigned channels, not digital superpower on their first-adjacent channels. These three-channel-wide interference generators are only eclipsed by their five-channel-wide AM brethren.
I also don't like the idea of increasing HD power. In fact, I'd like the HD to be adjusted so that you could easily pick up ......
- using a radio with the selectivity of a crystal set (and NO multiple tuned circuits - just *ONE* cheapie-grade tuning capacitor *OR* an adjustable antenna coil)
- a 1-3 uV/m first-adjacent analog signal (or whatever would require a 1/2-km longwire just to bring the signal up *TO* the radio's noise floor, on a radio that without the longwire would still be sensitive enough to get a 20 dB SNR on a 100 uV/m signal, or the sensitivity of the portables with 8" ferrites (CCRadio, Superradio, PR-D5, etc))
- while sitting so close to the HD station's transmitter that, for example, R. Fry's PL-310 would exhibit behavior like this or this (DSP lockup - signal strength indicating 00/00 or nothing at all, tuning the radio does nothing) with NO antenna (even going as far as to disconnect the internal ferrite, and I'm guessing in those videos I have 50+ dB gain over the internal ferrite with the SAT + utility pole)
Also, couldn't HD (or at least its current incarnation) be done by opening the analog bandwidth at the transmitter (so the analog splatter sounds as strong as HD currently is, or opening the bandwidth up to pre-NRSC levels) and incorporating DSP in the receivers (if the SNR goes below 135 dB, mute the audio)? (That last comment is based on seeing other comments about HD signals being unreceivable at distances that the analog would still overload my radios.)
If HD worked the way I wanted it, you could clearly receive a signal in HD, using 1/10th the transmit power and a radio with the performance of a pocket crystal set, that on the analog would be a barely detectable (and too weak to identify) QRSS CW or PSK31 signal on a $500k communications receiver + 1 km antenna, and it wouldn't interfere with reception of analog (or other modes) signals on the same frequency even if to keep from getting an RF burn through the air you had to wear an RF shielding suit or something like that.
I'm probably less of a fan of HD radio than a rookie Red Sox hitter would be of facing Mariano Rivera with the season on the line, 2 outs, and he's not even the tying run at the plate.
- using a radio with the selectivity of a crystal set (and NO multiple tuned circuits - just *ONE* cheapie-grade tuning capacitor *OR* an adjustable antenna coil)
- a 1-3 uV/m first-adjacent analog signal (or whatever would require a 1/2-km longwire just to bring the signal up *TO* the radio's noise floor, on a radio that without the longwire would still be sensitive enough to get a 20 dB SNR on a 100 uV/m signal, or the sensitivity of the portables with 8" ferrites (CCRadio, Superradio, PR-D5, etc))
- while sitting so close to the HD station's transmitter that, for example, R. Fry's PL-310 would exhibit behavior like this or this (DSP lockup - signal strength indicating 00/00 or nothing at all, tuning the radio does nothing) with NO antenna (even going as far as to disconnect the internal ferrite, and I'm guessing in those videos I have 50+ dB gain over the internal ferrite with the SAT + utility pole)
Also, couldn't HD (or at least its current incarnation) be done by opening the analog bandwidth at the transmitter (so the analog splatter sounds as strong as HD currently is, or opening the bandwidth up to pre-NRSC levels) and incorporating DSP in the receivers (if the SNR goes below 135 dB, mute the audio)? (That last comment is based on seeing other comments about HD signals being unreceivable at distances that the analog would still overload my radios.)
If HD worked the way I wanted it, you could clearly receive a signal in HD, using 1/10th the transmit power and a radio with the performance of a pocket crystal set, that on the analog would be a barely detectable (and too weak to identify) QRSS CW or PSK31 signal on a $500k communications receiver + 1 km antenna, and it wouldn't interfere with reception of analog (or other modes) signals on the same frequency even if to keep from getting an RF burn through the air you had to wear an RF shielding suit or something like that.
I'm probably less of a fan of HD radio than a rookie Red Sox hitter would be of facing Mariano Rivera with the season on the line, 2 outs, and he's not even the tying run at the plate.
We called that a "tershiary tone" later on.Savage said:
It was the forerunner of PowerPoint presentations. The engineers and sales staff must have been beside themselves when they found out they could just start the slide projector and cart machine and sit back and let it do all the work.
Jeff in Sa-ra-so-ta!
What's a dBc??
Does it affect the signal of a station
Does it affect the signal of a station
MarioMania said:
It's a measurement unit...decibels relative to carrier level. A negative number means the signal being measured is below carrier level by the numbered amount.
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