FCC gives AM brodcast stations OK to try controlled carrier

[k4kyv]

Of course, they have a fancier name for it, Modulation-Dependent Carrier Level.  One system reduces the carrier at low percentages of modulation while another reduces the carrier up to 3 dB at high percentages. Harris Corp. and WOR have recently claimed success with experimental broadcasts.  Reportedly, it has been in use by short wave broadcasters in Europe for several years.

The purported advantage to broadcasters is a substantial reduction in the electric power bill.

http://www.broadcast.harris.com/productsandsolutions/RadioTransmission/AMTransmitters/AMTransmitterPowerReductionAlgorithms.asp

[kb3ouk]

The purported advantage to broadcasters is a substantial reduction in the electric power bill.

they might as well just run double sideband suppressed or reduced carrier.

[ssbothwell KJ6RSG]

i think part 15 operators have been allowed to do carrier current for years (with severe power limitations of course).

i was under the impression that carrier current is only useful in small enclosed areas like office buildings or university dorms. is that not the case?

[KM1H]

Who is talking about carrier current? The last time that was popular for hams was during WW2.
Currently the power utilities are trying to get Internet working on the wires

[W7TFO]

Aw, Sol is just cornfused.

Controlled carrier ain't the same as carrier current radio.

Controlled has the carrier power linked and following the syllabic rate of the modulation.  An old trick to save watts on AM.  Sounded like crap back then.

He knows what carrier current is already.

73DG

[ssbothwell KJ6RSG]

ahh whoops i misread that pretty badly. can i blame that on a sinus headache?

[Jim, W5JO]

Given the programming and listners on AM these days, it won't matter much what method they use so long as it is understandable.

[Steve - K4HX]

Now, now! We're not allow to claim AM broadcast is dying here.  

[W7TFO]

Nah, it's not dying, but it IS getting absolutely unintelligible...

Even with perfect fidelity, if one can get it anywhere...

73DG

[KM1H]

I hate it when some damn bible thumper from Albany overides my favorite oldies station on 1540

[K1ZJH]

WOR?  That is surprising.... I wonder how controlled carrier modulation works
with the HD sidebands?  WOR was one of the first NY stations to adopt
the IBOC (I'm Big On Crap) technology. These are dark days for AM.

Pedro

[kb3rdt]

People in Alaska are using it for some time I got an Email about from ARRL be Like screen modulation but using transisters not Tubes..

[flintstone mop]

Has anyone actually monitored a station using this newer method of carrier control??
Or is it just conjecture from the old days that it's gonna suck??

IBOC is dead for AM broadcast. There wasn't clear thinking on that one. With skip and mixing / interfering with other markets.
I will say that IBOC on AM hangs in there better than FM. I can drive 25 miles listening to the one local AMer using IBOC and no drop-outs. FM is constantly flipping back and forth from the multipath.....IF you're in a big city with many high power FMs then IBOC shines.........nice to hear other programming choices on the HD-2....I swear it's CD quality audio.......not squashed processed FM audio.
Fred

[W2PFY]

IBOC is dead for AM broadcast.

If this is the case, why doesn't it go away? Minor hi-jack going on here

[K1ZJH]

CBS stations are major investors in the technology.

Hard to admit defeat?  It's like falling in love with a stock that you're
losing your shirt on. You know you sell and recoup some losses,
but you can't letgo   AM Stereo made more sense.

[kb3rdt]

this what you Talking about!


http://www.youtube.com/watch?v=7KtJxHN2cFE

[ke7trp]

Dennis,
 So with "AMC",  During no modulation, the carrier is a full 10KW.  But as modulation increases the power Drops down to 5KW.  His wording is confusing me. 

A 10K Transmitter would be 10KW carrier with just under 30KW peak power (according to BIRD).   

Does the carrier drop down to 5KW but the peak output power modulated stay the same at just under 30KW?  In other words, ONLY the carrier is the only thing that is changing or is the peak power Droping down with the carrier?  The idea being that the BIG carrier would clear the frequency at no to low modulation but with the high level modulation, you do not need that much over all power?

I would really enjoy having a KW of carrier during pauses and no mod and then when I was speaking still have the correct carrier to 1500 watt ratio.  The only way I see to do this is to vary my plate volts. HMMM.

C

[WB4AIO]

Back when the Christian Science Monitor was running a SWBC station, they used controlled carrier to save on the power bill. I believe that Brown Boveri made such transmitters at the time, though I don't recall if that was the kind that CSM was using.

It did compromise the reception quality to the point where it annoyed me, but the vast unwashed probably couldn't tell the difference.

Controlled carrier, even when it isn't inherently distorted as it often is, adds hard-to-predict AGC system artifacts at the receive end. It takes away one advantage of AM: a steady reference for receiver gain setting so that the received audio levels track the transmitted audio levels, all without a rise in received noise between syllables.

If the broadcasters want to save power, they'd probably be better off just reducing their power by half, though a 3 dB worse signal to noise ratio isn't exactly desirable these days, with rising digital hash everywhere (which could have been prevented by the FCC; another topic though). But then Harris wouldn't be able to sell any shiny gizmos.

The fact that the power bill is a much larger consideration than it used to be is quite an indicator of the immense decline of the Standard Broadcast Band.

Had independent broadcasters and the FCC insisted on migration to a dedicated digital band twenty or more years ago instead of following the wishes of the big chains and hanging their fortunes on the almost unbelievably retarded IBOC turkey, then the stations would probably be prospering, the remaining Standard Broadcast Band users would have far less crowding to deal with -- and there would be no buzzsaws driving even more people into the arms of mp3 players.


Happy 2012,


Kevin, WB4AIO.

[Jim WB5WPA]

Has anyone actually monitored a station using this newer method of carrier control??
Or is it just conjecture from the old days that it's gonna suck??

IBOC is dead for AM broadcast. There wasn't clear thinking on that one. With skip and mixing / interfering with other markets.
I will say that IBOC on AM hangs in there better than FM. I can drive 25 miles listening to the one local AMer using IBOC and no drop-outs. FM is constantly flipping back and forth from the multipath.....IF you're in a big city with many high power FMs then IBOC shines.........nice to hear other programming choices on the HD-2....I swear it's CD quality audio.......not squashed processed FM audio.
Fred

That's been my experience too:


http://www.youtube.com/watch?v=91BPPnozeIs


Well, maybe not quite the same come to think of it ... KLIF has since discontinued IBOC on AM and is/was riding an FM last I knew and the FM was marginal from the get-go where there was at least a 'clean' AM IBOC when there was no lightning ...

[kb3ouk]

Dennis,
 So with "AMC",  During no modulation, the carrier is a full 10KW.  But as modulation increases the power Drops down to 5KW.  His wording is confusing me. 

A 10K Transmitter would be 10KW carrier with just under 30KW peak power (according to BIRD).   

Does the carrier drop down to 5KW but the peak output power modulated stay the same at just under 30KW?  In other words, ONLY the carrier is the only thing that is changing or is the peak power Droping down with the carrier?  The idea being that the BIG carrier would clear the frequency at no to low modulation but with the high level modulation, you do not need that much over all power?

I would really enjoy having a KW of carrier during pauses and no mod and then when I was speaking still have the correct carrier to 1500 watt ratio.  The only way I see to do this is to vary my plate volts. HMMM.

C

ok, first, dropping the carrier level during modulation then running it back up full during no modulation sounds a little dumb to me but i could see the point behind doing it that way. running full carrier during pauses in modulation would keep the background static noise down between syllables, but would seem to me like the amount of noise during modulation would increase. by reducing carrier between periods of no modulation and bringing it back up for modulation, you would have background static bleeding through when there was no modulation, which doesn't matter since there is obviously nothing to listen to when the transmitter isn't being modulated, but then there wouldn't be as much noise during modulation because the carrier was back up to full power. second, yes, the carrier is the only thing that is being cut, the peak power is the same. a good example would be how some of the transmitters at WBCQ work. 7490 is the only full carrier AM transmitter they have. 5110, 9330, and 15420 are running compatible sideband. FCC HF rules say a station running SSB for HF BC work has to have 50 kw PEP or more. those transmitters are putting out 50 kw peaks on one sideband, but are running a carrier that is down something like 6 dB from the peaks. it's not using as much power as full AM, but it is still receivable on an AM receiver as well. and as for having a KW carrier but dropping it back to 375 watts for 1500 watt peaks on modulation, it would be neat to try rigging up a VOX circuit that would drop the B+ on the tube down to what is needed to make 375 watts as soon as you strt talking, or what may be a little more realistic would be simply controlling the amount of drive going to the tube. pick a tube that can do a KW out then rig up a VOX circuit or something that way when you start to talk, part of the drive from the exciter is dumped through a load, and only enough to make 375 watts is passed into the final amp.
shelby

[W7TFO]

You guys have it backwards.

Carrier ramps up to match the modulation.

Goofy thing it is.

73DG

[ke7trp]

Dennis. Watch the Video.. on the scheme called AMC, the carrier is full power with no mod but Drops during modulation. The man explains it. I wanted to know if the peak power is staying the same with this scheme or if they are JUST lowering the carrier?

C

[Jim WB5WPA]

You guys have it backwards.

Carrier ramps up to match the modulation.

Goofy thing it is.

73DG

Oh that will work well on a weak station - what with the AGC 'opening up' IF gain amplifying adjacent channel (usually mild) splatter or IBOC sidebands (like when listening to KLBJ on 590 from north of Dallas and IBOC hash is ever-present from 620 KMKI) on 'quiet' program segments (due to pauses in speech, etc).

There goes the "AM Quieting" effect.

Is this the AM band station owners making their last stand, the paring back of the last 'direct expenses' necessary (for electricity) to run the broadcast transmitter of the station, as they are now into directly affecting 'transmit signal characteristics' (without outright filing for a transmit power reduction) ... until the last listener migrates to FM, MP3's, XM/Sirius (?) or 4G/LTE program content streamed to their cell phone?

(That was a question above BTW.)

Jim de WB5WPA

[kb3ouk]

i would assume the peaks are staying the same, and the carrier is just being reduced. it would be dumb to reduce the carrier AND the peaks at the same time, really in that case it would be the same as if i were talking to someone on my transmitter and turned the carrier knob back when i started to talk then turned it back up when i was done.

[kb3rdt]

control carrier transmitt the carrier is reduced but sidebands are not the carrier get greater when the sandband power amplitude like screen modulation