FCC gives AM brodcast stations OK to try controlled carrier

[W7TFO]

OK, the technology is a bit diffused here.  I was referring to the older system.

The photos show the vintage "controlled carrier" modulation results of yore.  The carrier RISES under modulation, drops in quiescent periods.

The new idea for AM BC operation may be similar, I have no interest in it presently.  In other words, neither do any of my client BC stations.

The first idea didn't pan out.  The latter may, time will tell.

AM IBOC is reportedly incompatible with it as well per conversations with my peers. 

73DG

[WB4AIO]

[...]
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.

As insane as it sounds, that is exactly what they are doing.

Death throes and self-delusion go together.


73,


Kevin, WB4AIO.

[W7TFO]

Tain't no free lunches....

73DG

[ke7trp]

On Solid state this would be much easier.  But the idea of a BIG Carrier of say 1000watts that would fall back to 400 when I was talking and 1500 PEP is really kind of neat. It would sure clear the frequency and keep the pauses between words clear.

C

[KX5JT]

On Solid state this would be much easier.  But the idea of a BIG Carrier of say 1000watts that would fall back to 400 when I was talking and 1500 PEP is really kind of neat. It would sure clear the frequency and keep the pauses between words clear.

C

It seems like it's working for the Alaska Public Broadcasting and the engineer says they are saving about 30% on their electric bills for the transmitter.

[W7TFO]

I'd like to watch an 'S' meter with this at work.

I'd also like to audition it 'before & after' on a good vintage receiver.

Come to think of it, I guess good vintage receivers all had 'S' meters.

73DG

ps...Clark TRP can't possibly be worried 'bout his electric bill.....

[WB4AIO]

It seems like it's working for the Alaska Public Broadcasting and the engineer says they are saving about 30% on their electric bills for the transmitter.

They could save 50 per cent. if they just ran half power, and with no audio/AGC artifacts, and with a lot less complexity.

What do they gain for all this complexity? -- a barely discernible 3 dB of quieting between words and between songs? -- seems pretty silly to me.

My interpretation: They're really running their 10 kW transmitters at 5 kW but refusing to admit it -- and paying for the privilege.


With all good wishes,

Kevin, WB4AIO.

[K1ZJH]

http://www.nab.org/xert/scitech/pdfs/rd092611.pdf

http://transition.fcc.gov/Daily_Releases/Daily_Business/2011/db0913/DA-11-1535A1.pdf

Carrier appears to rise with modulation similar to controlled
carrier from what I can see??

Pete

[k4kyv]

One explanation I read was that the amplitude of the carrier is digitally controlled to more accurately follow the syllabic rate of the audio than what is obtainable with conventional controlled carrier, and algorithm is designed so that with low percentages or no modulation the carrier rises back to or near full amplitude to keep the channel quiet, but in the region of average modulation density (somewhere around 20-30% percent), the carrier is at a minimum so that the audio is actually modulating the reduced carrier near 100%, and as the percentage of modulation of the equivalent steady carrier goes up, the actual carrier is increased to accommodate the  audio on up to what would be 100% modulation on a normal full carrier transmitter.

[flintstone mop]

this what you Talking about!


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

PERFECT video and explanation!!!

And they use the old fashioned 'O scopes to monitor the new variable power transmitters.

[KA3EKH]

Don’t know about all this, thing around here that’s killing AM is that the land required for the tower site and transmitter is worth more then the revenue that the station can produce. Have a couple Harris DAX-5 solid state monsters at my two AM stations that are fairly efficient and way cheaper to run then the old MW-5 tube transmitters that they replaced because they would want new modulator tubes every year so now the only expense is the electric. Talk or sports radio all runs from a small server in a rack back at the studio so there are no labor cost or other operational cost but would assume if your running a 50 kW station in a real market and knowing how cheap all the AM people are every cent they can save is important but most stations bought new solid state transmitters in the last ten or so years and cant see them running out and buying a new transmitter, maybe this can be adapted to the carrier control in modern PDM or PCM transmitters? Back in the day of analog television someone came out with this stupid box that you had to install on your klystron that did something during the sync pulse to give you increased efficiency and from what I recall it involved lots of HV wiring and danger! Fortunately my one big television site used IOX tubes and did not have that but tell the GM they can save $50 a year for the owners and being that they don’t have to do the work in the middle of the night yea you’ll be installing it.

[The Slab Bacon]

You guys have it backwards.
Carrier ramps up to match the modulation.
Goofy thing it is.
73DG

Thank you, Dennis! ! ! ! ! ! ! !  The carrier starts out low then ramps up as the modulating audio level increases! (Just think DX-60) It can be a real pain in the arse to get tweaked out right at times, but can be made to sound good if one is patient and dilligent in it's set up.

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

controlled carrier and screen modulation are often used together, but not necessarily one and the same. They are two seperate animals. the DX-60 (and a few others) have made them synonymous. But that is not always the case!

A good example is my big HB transmitter. It runs along at 375w of carrier    all day
and easily makes 125% positive peaks. And it is screen modulated!! but not controlled carrier. (Actually it is screen and control grid biass modulated) And no one ever complains about how it sounds. (Which also breaks the old myth that you cant make 100% mod with screen modulation)

Broadcashters going to controlled carrier systems only seems natural in these days of everything "going green". As far as I am concerned, the only thing green about it is the feeling it all gives you in the pit of your stomach as you are about to hurl!

[WBear2GCR]

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

really? can't hardly hear them here in the Albany area... ha!

                 _-_-bear

[kb3rdt]

Some of us have carrier controlled txers like the DX-60 well it be like hearing that or far worst?

[K3ZS]

Maybe not relevant, but I remember the DX-40, the bassy audio and the S-meter bouncing around with modulation, a lot worse than the DX-60.

[flintstone mop]

Some of us have carrier controlled txers like the DX-60 well it be like hearing that or far worst?

It would not be as bad as the older Ham transmitters. With the time constant of a BC AM receiver it is un-noticeable. It's only changing the TX power by 3dB...The video link to Youtube is lengthy but very informative from engineers who are Amateurs and aware of the 'old style' carrier controlled transmitters.

[k4kyv]

controlled carrier and screen modulation are often used together, but not necessarily one and the same. They are two seperate animals. the DX-60 (and a few others) have made them synonymous. But that is not always the case!

The first controlled carrier rigs when the concept was introduced in the 1930s were plate modulated.  One scheme was to let the class B modulator plate current control the carrier level. The plate current passed through one winding of a saturable reactor, while the other winding was in series with the primary of the plate transformer for the rf final power supply.  The increase in modulator plate current caused the core to saturate and thus decrease the inductance of the winding in series with the final amplifier plate transformer, which in turn decreased the inductive reactance and voltage drop to give the rf plate voltage a boost.  Somehow the winding with the DC passing through it was balanced for a.c. to keep 60~ from being introduced back into the class B DC plate supply.

A cheap and dirty method was to use one big power supply for modulator and final, with approximately double the DC output voltage of the normal power modulator or rf final power supply, and simply wire the DC plate circuits of the final and modulator in series.  The class B modulator DC plate circuit acted like a variable resistor in series with the rf final plate supply.  With increased modulator plate current, the effective series resistance dropped, supplying more voltage to the rf final. Or another way of looking at it, since the modulator and final were in series across the same power supply, any increase in modulator plate current had to result in an identical increase in rf final plate current. Basically, series modulation at the syllabic rate. It probably had a lot of distortion, since the class B modulator was operating with extremely poor voltage regulation.  It probably worked better using zero-bias modulator tubes.

[k4kyv]

controlled carrier and screen modulation are often used together, but not necessarily one and the same. They are two seperate animals. the DX-60 (and a few others) have made them synonymous. But that is not always the case!

The first controlled carrier rigs when the concept was introduced in the 1930s were plate modulated.  One scheme was to let the class B modulator plate current control the carrier level. The plate current passed through one winding of a saturable reactor, while the other winding was in series with the primary of the plate transformer for the rf final power supply.  The increase in modulator plate current caused the core to saturate and thus decrease the inductance of the winding in series with the final amplifier plate transformer, which in turn decreased the inductive reactance and voltage drop to give the rf plate voltage a boost.  Somehow the winding with the DC passing through it was balanced for a.c. to keep 60~ from being introduced back into the class B DC plate supply.

A cheap and dirty method was to use one big power supply for modulator and final, with approximately double the DC output voltage of the normal power modulator or rf final power supply, and simply wire the DC plate circuits of the final and modulator in series.  The class B modulator DC plate circuit acted like a variable resistor in series with the rf final plate supply.  With increased modulator plate current, the effective series resistance dropped, supplying more voltage to the rf final. Or another way of looking at it, since the modulator and final were in series across the same power supply, any increase in modulator plate current had to result in an identical increase in rf final plate current. Basically, series modulation at the syllabic rate. It probably had a lot of distortion, since the class B modulator was operating with extremely poor voltage regulation, and  likely worked better using zero-bias modulator tubes.

[Jim WB5WPA]

this what you Talking about!


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

PERFECT video and explanation!!!

And they use the old fashioned 'O scopes to monitor the new variable power transmitters.

The quoted figure for a remote generator 10KW transmitter, his diesel cost is $6.50/gal, at 23 gallons a day works out to a cost of about $822/day and a total fuel cost for a year at $300,000.

The engineer interviewed did bring up some good points about the dynamic loads presented to the AC line depending on the type of 'power control' mode selected (as there are two types), and in the case he cited with the generator, this can drive the generator's voltage regulation control bananas as it 'hunts' for the proper drive to the generator exciter winding ... also the various substations use solid-state 'tap selection' (on transformers) and can be driven nuts with highly dynamic loads (like voice or speech).

Interesting vid.

de Jim WB5WPA