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Philly's big guns: 990, 950 1210, 1060, 1540 could save a bundle

A

amfmsw

The FCC has finally 'approved' a modulation method that's been around for decades, in my mind. This method would save these big signals tens of thousands in energy consumption annually.

My sarcasm of 'approval' stems from my conviction that this is truly based on a 1940's RCA Patent that was abandoned. WIBG used it in their RCA Ampliphase transmitters installed in 1958. The premise being to hold back current on quiet passages and let 'er fly when fully modulated, thus saving electricity...which it did by the way.

Here's the story: www.rbr.com/radio/fcc-paves-way-for-ams-to-save-by-going-green.html

sounds like the same thing to me.
 
It's "controlled-carrier AM" and it has indeed been around for decades. The concept is that a huge proportion of the energy consumed by AM transmitters comes from generation of the carrier, to which the audio energy is then added. The carrier is only needed to deliver the audio intelligence; in the space in between the densely-modulated parts of the envelope the carrier represents wasted energy. By drastically reducing the carrier in unmodulated periods the AC input to the transmitter is conserved.

The good news - yes, this can save AM stations a ton. So guess what the downside is?

Did I hear a voice in the back say, "HD-AM interference?" Give that man a gold star. The problem here today is QRM and QRN from everything from power lines to computers to what is arguably the worst offender....HD. As the carrier level gets throttled back, the objectionable noise will ramp up as the receiver AVC opens up in search of signals.

Unless you're on a really quiet channel 24-7, you may save electricity at the expense of losing still more listeners. This is why the FCC experimented with controlled-carrier up in Alaska, where the interference and noise are lower.
 
Some of the value of this depends on the future of the AM band.

If the rest of North America becomes like Alaska (fewer, stronger, unlimited hours stations), this has a chance.

If, on the other hand, we see this become an even more crowded, dollar-a-holler amateur band (250 watts day, 6 watts night) in the future, then it won't work.

On the other hand, the business viability of the band, in any event, may depend on this.
 
With respect I say: it's hard to see why.

We're a high-power AM, 20kw at 1040, with a pretty modern all solid-state transmitter (NAUTEL AMPFET25.) We also have some of the highest utility rates in the country - 12 cents/kwh or more. If our electric bill were to drop in half, I would certainly welcome that, but not at the expense of not having the best signal possible. If I have to compromise intelligibility or performance of my signal with certain radios, it's not worth the $12,000 annual savings.

And controller-carrier for lower powers just doesn't make sense. The savings are too small. I could see this as a concept for 100kw or 250kw shortwave stations where the listeners tolerate high QRM/QRN as a matter of course, but today's typical listeners expect a signal which is acceptably strong and reliable. As noted, instead of being a "saviour" for AM, HD Radio has heaped another interference curse on top of an already bad situation with power line, LED traffic signal, dimmer and computer noise.

If the financial viability of our AM depends on saving 12 grand, I'd better go find another line of work.
 
I haven't communicated well. Saving on power isn't what will influence the viability of the band. A plan for the future allocations of frequencies may do so.
 
observer2 said:
I haven't communicated well. Saving on power isn't what will influence the viability of the band. A plan for the future allocations of frequencies may do so.
Click to expand...

And the FCC is not interested in giving away spectrum space for broadcast radio. They're hoping it will die of its own doing.
 
amfmsw said:
My sarcasm of 'approval' stems from my conviction that this is truly based on a 1940's RCA Patent that was abandoned. WIBG used it in their RCA Ampliphase transmitters installed in 1958. The premise being to hold back current on quiet passages and let 'er fly when fully modulated, thus saving electricity...which it did by the way.
Click to expand...

Just curious, how did the transmitter meet carrier shift requirements of the day?
 
The 990 in Providence RI, then WLKW, a 50 kW daytimer protecting WIBG, also ran a BTA-50G Ampliphase. The format was Beautiful Music. Mantovani, Frank Chacksfield, and the 101 Strings sounded great out of that rig.
 
The Ampliphase was a great idea - in fact, the concept far outpaced the available technology when RCA rolled it out in late 1955. WIBG was in line for one of the early 50G's.

The Ampliphase concept eliminated the modulation transformer and the necessity of having extremely high-power audio amplifiers to add the modulation intelligence to the 50kw carrier. In the Ampliphase system two RF amps were offset by a small phase difference, and an "exciter" - yes, like in FM - varied the phase angle of the two RF chains in direct proportion to the modulation. Then the two RF signals were recombined to create a modulated 50kw envelope.

In theory the system provided extremely high-fidelity audio and an ease of modulation unattainable with high-level plate-modulated transmitters - as an added bonus, the 50G was much more efficient with electricity consumption. In practice, the Ampliphase transmitter had several issues which were never fully corrected through three series of rigs (50G, 50H and 50J) until RCA exited the high-power AM business in 1978. The transmitters were very load-sensitive, requiring a pretty pure symmetrical and non-reactive antenna common point, without which distortion and lower modulation density would appear. The aging and random drift of the 20 vacuum tubes in the exciter chassis adversely affected performance as well. These faults earned the rigs the derisive nickname "Amplifuzz" with frustrated engineers and programmers. RCA eventually came out with a very complex solid-state exciter in the 50J series around 1969, but by then PWM technology was already outpacing phase modulation. Few 50G and 50H owners bothered to update to the new exciter; I don't know if WIBBAGE ever did with their 50G. IIRC when I was there briefly in the spring of 1974 the tube exciter was still in place. Maybe Mr. Tetro can tell us.

So, in short - great idea theoretically, but in the real world, a maintenance hog. Indeed, at its best, an Ampliphase sounded fantastic.
 
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