AM power VS SSB power

[R. Fry SWL]

Looks like the carrier remains steady regardless of modulation, and its amplitude is greater than that of any sideband component at any time.  The carrier amplitude appears to increase and decrease with modulation only when the display lacks the necessary selectivity to discriminate between the carrier and sidebands.

Just to note that DSB, full-carrier, broadcast band AM transmitters made by Harris Corporation use digital techniques to control discrete, solid-state r-f amplifier modules to produce the modulated waveform directly.

Here thanks to Jim Hawkins is a description of this technique:

RF OUTPUT

Each output module is fed with a square wave from the driver section and outputs a square wave. The square wave output from each module is fed through a coil wrapped around a toroid. A pipe runs through the center of all the toroids, acting as a secondary transformer winding for all the toroids, which picks up the combined output of all energized toroids. The toroid filters most of the square wave harmonic components out, leaving an almost pure sine wave which represents the radio signal. There are other filtering networks before it gets to the output network in the transmitter, so by the time it gets to the output, the signal is a pure sine wave.

You can think of the modules as pistons in an engine, each putting out bursts of power, and the toroid coil as a flywheel which smooths the oscillation. In fact, if just one burst of power were applied to the toroid, it would continue to "ring" momentarily just as a fly wheel would continue to spin if you gave it one push. Without continued pulses of energy, the energy would eventually spin down due to losses. In the case of a flywheel, the losses are due to friction. In case of the toroid, the losses are due to resistance in the conductors. A toroid transformer is a donut shaped piece of iron, with coils of wire wrapped around it.

When there is no modulation (silence), 48 modules will be turned on simultaneously to generate approximately 55 KW (5 KW is lost on the way to the antenna). To modulate the transmitter, modules are turned on and off. As you turn more modules on, you have more RF carrier and when you turn more off, you have less RF carrier.

The digital technique used in these transmitters is extremely efficient (90%) as opposed to about 64% with the old high level plate modulated vacuum tube transmitters. That is, the older transmitters might use 78,000 watts to obtain a 50,000 watt output signal where the modern, solid state transmitters might use 55,000 watts to obtain a 50,000 watt output signal. That's a 23,000 watt savings and quite a difference in the electric bill! The voltage applied to the output units is 240V and current runs about 300 AMPS. The power supply is fully contained within the cabinet and basically consists of a transformer which steps 440 VAC down to 240 VAC with some big diodes for rectification.

From power line to r-f output, the efficiency is approximately 78% for these transmitters.

[kb3ouk]

Looks like the carrier remains steady regardless of modulation, and its amplitude is greater than that of any sideband component at any time.

The carrier amplitude appears to increase and decrease with modulation only when the display lacks the necessary selectivity to discriminate between the carrier and sidebands. A monitor scope with the rf sample directly feeding the deflection plates , and a Bird 43, lack that selectivity.

So what's the legal power limit at a multi-transmitter field day site?  Is the output power of each transmitter treated as a separate entity, or is the transmitter power the sum total of the outputs of all the transmitters operating simultaneously, added together?

If each of the transmitters is to be treated separately, then the Timtron method of AM power measurement is correct.

If the vector sum of the output power of all the transmitters added together is used for the power calculation, then the ARRL method of AM power measurement prevails.

I'm guessing you mean by treating the carrier as if it were separate from the sidebands, which would put the legal power at 3000 watt carrier, with 1500 watts sideband power. Or 1000 watts carrier 500 watts in the sidebands if you treat it as adding the sideband power to the carrier power. Now if you take the ARRL's method into consideration, going on the sum of all transmitter powers together, then in that case they would even be running illegal power, with 1500 watt transmitters on something like 6 bands at once, that's 9000 watts PEP altogether.

[WD8BIL]

....then in that case they would even be running illegal power, with 1500 watt transmitters on something like 6 bands at once, that's 9000 watts PEP altogether.

Using that logic, operating a multi-multi contest station with legal limit at on each band would be illegal. We know that's not the case.

[kb3ouk]

Which proves my point.

[n1ps]

Well I have been following this thread and reread some of the old ones on the same subject more or less.  Always good to get everyone's opine on the PEP concerns.  I tend to agree with Steve and Al on this one.  When you read the part 97 (PEP) language, the FCC is speaking about a scope based voltage measurement of RF power.  Not spectrum analyzers.  This is probably because they realized that Joe Ham probably uses a scope at least occasionally for his HF set as a monitoring device or perhaps uses a watt meter of some variation. Few have the capability to exceed 1500 PEP. 

Its true that some of the SSB appliance ops don't know which hole to plug an antenna connector into, but the equipment they use takes care of that for them or they blow things up.  The old power input code could not address SSB adequately, so here we are, us AMers, stuck in a time warp.  We have to live with PEP and try to interpret it as best we can. 

By following the PEP formula and using a scope you will be in the neighborhood as far as legal limit.  Al presented one way to accomplish this in an earlier post.  If you choose to use some other method other than the PEP formula to arrive at your maximum power and it is multiples of the 375 watts carrier....you are on your own.  Because we have no ERP limits there really is no good way for the radio police to monitor your speed limit (that I am aware of).  But for those that are running thousands of watts....pushing the speed limit....be careful. I don't think the FCC really cares anyway.  Their plate is full in other arenas.  If they really cared Baxter would have been shut down years ago.  We are in a different world now...the FCC monitoring stations are  shut down, the Gmen are no longer driving around snooping for violators (and demanding a transmitter site inspection) and a magazine is policing the ham bands.

p

[ND9B]

Just a side note: I have an Ameritron AWM-30 "Peak Reading SWR/Wattmeter" here with a K7DYY AM Legal-Limit transmitter. This meter is one of the very few TRUE peak readers. It reads 370 watts on the carrier (with the mic muted), and 1500 watts when I talk. This follows the 4X carrier rule.

Bobby Dipole ND9B

[Opcom]

So, does the single-frequency carrier vary in amplitude with the modulation, or does the carrier remain steady, while the modulation produces adjacent sideband energy components along side the carrier frequency?

When modulated, the frequency is offset from the carrier by the frequency of the modulating signal (leaving complexities out of it..) but the scope has no bandwidth resolution so it can't show you that the RF cycle is slightly distorted, according to the modulation, from its supposed sine wave.

Who has something like a spectrum analyzer with a .01Hz resolution bandwidth and can generate an AM signal low enough in frequency say 3KHz with a 0.3Hz AM modulating wave so that this can all be viewed and put on video? even then it will be argued..

[k4kyv]

The old power input code could not address SSB adequately, so here we are, us AMers, stuck in a time warp.  We have to live with PEP and try to interpret it as best we can. 

You are basically saying they screwed AM because the feecee couldn't deal with SSB adequately. They obviously didn't try very hard. The rulemaking bureau basically dodged the issue and went on to present fraudulent arguments to the cluless non-technical lawyer type Commissioners to have them to rubber-stamp their predecided agenda.

The Canadians were able to do it in their regs by adding a few simple words, defining slopbucket in terms of p.e.p., but  leaving carrier modes like AM defined in terms of carrier power. I guess Canadians are smarter than United States-ese.

[K5UJ]

Slopbucket was around for years before the power rule changed.  if they changed the rule because of it, they dragged their feet for around 30 years.  I recall there was a period of a few years where the SSB power limit was 2 KW DC input and everyone else was 1 KW.  I think that's right.  But they couldn't live with that for some reason.

[Steve - K4HX]

Yes. Depends whether you are viewing the signal in the time domain or the frequency domain. Don't confuse the signal changing with changed the method of viewing the signal. One method is not "right" or better than the other.

So, does the single-frequency carrier vary in amplitude with the modulation, or does the carrier remain steady, while the modulation produces adjacent sideband energy components along side the carrier frequency?

[WA3VJB]

... and a magazine is policing the ham bands.

Only those who are duly deputized.

[ND9B]

So, does the single-frequency carrier vary in amplitude with the modulation, or does the carrier remain steady, while the modulation produces adjacent sideband energy components along side the carrier frequency?

Theoretically the carrier remains constant. You will actually see this with a spectrum analyzer or a narrow filter tuned to the carrier. Kind of freaky to see the envelope go to zero when the carrier is still there!

Bobby Dipole ND9B

[Steve - K4HX]

Remember, nearly all spectrum analyzers are not real time. The leve you see on the display is an average over some time constant.

AM pulse modulate a carrier with a square wave with a period of 10 seconds. See if the carrier goes away. 

[The Slab Bacon]

This subject has been discussed ad nauseum! ! ! ! ! ! ! ! How many more times does it have to be discussed    Just run what ya got and be done with it! ! !  No one is going to knock on your door to check your stuff.

We could be discussing something more interesting like pickled eggplant   

[k4kyv]

Slopbucket was around for years before the power rule changed.  if they changed the rule because of it, they dragged their feet for around 30 years.  I recall there was a period of a few years where the SSB power limit was 2 KW DC input and everyone else was 1 KW.  I think that's right.  But they couldn't live with that for some reason.

Actually it was never anything but 1 kw DC input, but popularly interpreted in ham circles as 2 kw p.e.p.  The method for monitoring power input with slopbucket is to watch what the plate current meter reads on voice peaks. The pointer on the meter should not swing beyond the figure that  represents a 1 kw DC input reading. The feecee had a published policy (I don't think it was actually spelt out in the rules) that the meter should have a mechanical time constant of something like 0.25 seconds.  In other words, the ballistic characteristics of DC plate current meter was treated somewhat like a VU meter. It was assumed by the advocates of slopbucket that in order to get this swing with the average human voice, the p.e.p. input would be around 2 KW, so the "2 KW p.e.p." phrase began to show up in the appliance manufacturers' ads.

Thus, p.e.p. came into the amateur radio vernacular with the advent of commercially manufactured slopbucket leen-yars.  It allowed the manufacturers to run advertisements overstating the power capability of their amplifiers. An amplifier sounds bigger if it is rated at "2 KW p.e.p." than merely 1 KW.  Not unlike all the bogus peak power specifications used by stereo amplifier manufacturers to misrepresent their products (rubbish like "peak music power", ad nauseam), allowing a 20-watt amplifier to claim a rating of a couple hundred watts. I recall ads in QST that read something like: *2000 watts, with a footnote at the bottom of the page in fine print: * p.e.p."  Another one that was kind of hilarious, by National, IIRC, read "2000 watts p.e.p.".  This figure was based on the notion that with voice modulation, the peak power is about double the average power.  Of course this is not true; the peak-to-average ratio varies widely with the individual voice. I believe this ratio may be true with a two-tone test, but a human voice is a far cry from a two-tone test signal.

One of the first hints at what was upcoming appeared about 1982 in a CQ Magazine article that transcribed an interview with an FCC attorney (named McKinney, IIRC) who was acting as spokesman for the Private Radio Bureau.  This is an approximate quote, as I recall it: "One of the problems we need to fix is the archaic amateur power rule.  It is not so much a problem, as an embarrassment to the Commission..." I ran a news story reporting this in The AM Press/Exchange but few readers paid any attention to it. A few months later, the power rulemaking docket was released.

This subject has been discussed ad nauseum! ! ! ! ! ! ! ! How many more times does it have to be discussed     Just run what ya got and be done with it! ! !  No one is going to knock on your door to check your stuff.

We could be discussing something more interesting like pickled eggplant    

If you find this topic so boring, there is a little « previous/next » button at the upper right-hand corner; go on to the next topic or close the page.

If the subject is not revisited from time to time, there are newbies out there who will be led to believe that it was always the way it is now.  I have actually seen posts in threads in e-Ham and QRZ.com indicating that the writer was unaware that the 1500w pep rule didn't always exist, back to the 1930s or even 1920s. Already, the majority of current licensees undoubtedly didn't have tickets when it was 1 kw input, and most are probably unaware that it ever existed as such, and few current licensees are aware of the fraudulent and deceptive methods and procedure the Private Radio went through to instate the rule in its present form and allegedly reduce the historically legal AM power.

“Those who fail to learn from history are doomed to repeat it.”
-Sir Winston Churchill

[W7TFO]

Such narrow thinking.  Some countries don't go by IARU rules, like Saudi Arabia.

Powerhouse licensed hams abound some places.

So...who bloody cares how much oomph you use?

You're more likely to get into trouble with your speech content, overheard by DHS paranoids.

73DG

[DMOD]

I think we should adopt another poster's rule:

Paraphrasing, "Lite 'er up and run 300+ Watts."  

I like that much better than, "Measure the Vee squared Deevided by the ARE at the crest of one cycle of a modulated ARE F waveform."    



If'n the F and CC comes around I hope they bring a better scope than the one I have.  

Phil - AC0OB
  

[Ed/KB1HYS]

Just start with 1500 watts carrier, only modulate downwards. so 1500 watts carrier = no audio, and 100% moduation means no carrier.

I bet that would sound.... interesting.

[Pete, WA2CWA]

Just start with 1500 watts carrier, only modulate downwards. so 1500 watts carrier = no audio, and 100% moduation means no carrier.

I bet that would sound.... interesting.

Actually you can pretty much do that with many of the current transceivers on the market today. Check our "Modern Rigs" forum was discussions on "why does my Icom (Yaesu, etc.) xxx have downward modulation on AM". Bacon, WA3WDR, talked about this, http://www.qsl.net/wa5bxo/asyam/aam3.html (about 3 quarters down the page) what he called "reverse carrier control". What's nice about this is that with a modern day transceiver, and not over cranking your modulation gain control(s) to distortion levels, you can crank your drive to the linear up and not worry that you'll exceed the linear's plate dissipation levels. Of course, if you have lengthy pauses between words or syllables or have a tendency to doze off during a transmission, this probably won't work for you.

[ke7trp]

When you are bored,  Throw a carrier,  take a carrier watt reading, Calibrate your scope to two lines.  Then turn up audio until 4 lines total.  100% mod, now read your bird3P or accurate pep meter,  NIST, power master ect. 

Is the ratio 4 times?

C

[k4kyv]

Or just let the final run at a KW DC input, and let the power outpoot peak where it may.

[The Slab Bacon]

Or just let the final run at a KW DC input, and let the power outpoot peak where it may.

Isn't that kinda what I said? ?        

Just run that ya got and don't worry about it.......................  

[K5UJ]

Just run that ya got and don't worry about it.......................  

I agree but to put Don's point another way, it has to be discussed from time to time because there is a continual stream of hams who have been led to believe they must precisely measure their carrier power and if it is 1 milliwatt over 375 w. they'll wind up in prison.  To get them to the point where they realize what bs it all is, they firstly have to be made to understand that measurement and power in terms of AM operation are not simple cut and dry things.  Then they understand that the whole pep mess is ridiculous and from there they get the "run it and don't worry" part and instead, focus on clean audio, sidebands around 5 kc out, nice looking trapezoid and < 100% negative.  

[KE6DF]

Or just let the final run at a KW DC input, and let the power outpoot peak where it may.

And if the FCC ever checks you and complains, tell them you thought your peak was 1500 Watts because you believe in the quote: "talk softly, but carry a big stick"

[kb3ouk]

And that's if A) the FCC really cared, and B) the agent who checked your station even had any understanding of what was going on. I seem to recall seeing somewhere (maybe on this board) where an AMer's station was inspected by the FCC, and was running something like 750 watts carrier, but the agent didn't do anything since his power meter showed 750 watts, and that's under 1500, so the ham was good to go, the thing was the agent took the readings with a dead carrier, no modulation. So if that's the way things really work with them, you could almost run any amount of power, and as long as it was a clean signal, no one would bother you. You'd probably catch more crap from one of the ARRL's official observers if they hear you saying you were running over 375 watts than you would from the FCC.