The AM Forum

For legal limit output (1500W PEP), what would be the average output power of AM and SSB?

It must vary from voice to voice, but is there a rule of thumb for this?

Bobby Dipole ND9B

I believe it varies greatly between individuals.

To be accurate, you might say "without processing".

For my voice and using a linear amplifier, the average reading RF power meter shows about 1/4 of the PEP and the needle stays put and hardly wiggles at all. This seems consistent whether it was the mobile 800W amp, where the carrier setting was about 180W, or the NCL-2000 amp in the station, where the carrier is 200W. In both cases the movement is very slightly upward but only 5% or so.

Whether that means I have a "perfect" voice is debatable!

I believe the answer is different when the meter is reading a plate modulated transmitter instead of a linear amplifier.  When I had the Viking I, the RF power meter would deflect upwards when I spoke.

In all cases on SSB, my speech seems to deflect the meter to about 1/3 of the amp's peak power number.

I expect the next reply will be totally different.

The human male voice has a peak-to-average ratio (PAR) of about 14 dB on average (it will vary from this from one person to the next).

So for unprocessed (no compression, etc) audio, the "average" power output for SSB with 1500 watts PEP is about 60 watts PEP. Yes, I used average and PEP together.

For AM let's assume 1500 watts PEP is produced with 100% positive peak modulation. This means the carrier power would be 375 watts. So the average the average power is 375 watts when there is no modulation. This means to get to 1500 watts PEP, an additional 1125 watts of power comes into play but only at 100 percent modulation. Apply the 14 dB PAR for the modulation and the average power due to modulation is about 45 watts. So the total is 420 watts average.

Now I know why I don't get out too well. My PEP's are low......I guess more processing and a D-104 mic might help.

What  kind of instrument are you using to measure average power?  To measure true average (aka "mean") power, you need a square-law, or RMS-reading instrument.  Nearly all commercial "wattmeters" such as the Bird 43 and the numerous Hammy Hambone wattmeters are in fact rf voltmeters that work by simple rectification of the rf sample, but with a scale calibrated in "watts" when working into a specified resistive load, usually 50 ohms.  This assumes a pure unmodulated sine wave, and only with a pure sine wave will the instrument accurately read average power.  With SSB, the average power reading will be significantly low.  With AM, the instrument will indicate carrier power.

The reason for this is that a rectifier type rf instrument reads average rf voltage. However, average power is not average voltage × average current, nor {average voltage}² ÷ load resistance , but RMS voltage × RMS current (or {RMS voltage}² ÷ load resistance). This has lead to a lot of confusion because of misuse and misunderstanding of the terms.  BTW, there is no such thing as "RMS power". The proper term is average, or mean power.

By definition, RMS (root-means-squared), also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity, specifically the square root of the mean (average) of the squares of the values taken over a specified length of time.  The simplest and most familiar true rms reading rf measuring instrument is the thermocouple rf ammeter, which actually samples heat generating by the r.f. as it raises the temperature of a thermocouple.  Power is calculated by using the formula P=I² R.

True RMS-reading voltmeters have recently been developed commercially; therefore an average-reading wattmeter may be designed by calibrating an RMS voltmeter to a watts scale, using the formula P=V²/R.  Like the rectifier type "wattmeter",  these instruments are calibrated only to work into a specified resistive load. One such instrument, which is not cheap, is the Bird APM-16 (http://www.chuckmartin.com/category/Bird-APM-16-Wattmeters-48).  



Steve, you are correct about the SSB peak-to-average ratio with the human voice. But I believe you made a typo.  It should have simply read the "average" power output for SSB with 1500 watts PEP is about 60 watts.

Slopbucketeers run average power much greater than that either by using heavy processing, or by simply driving their leen-yars well into the flat-topping region, resulting in rf clipping and broad splatter.
 

Thanks for the correction Don. Yes, it's average not PEP.

I was listening to a converstaion between timtron and someone else friday night on the subject of what carrier level would give 1500 watts pep on AM. I heard three different answers:

375 watts- the ARRL and everyone's typical 4 times the carrier is PEP

1000 watts- 1000 watt carrier modulated 100% is 1500 watt PEP because one half the carrier power for audio added to the carrier, and finally...

3000 watts  :o :o :o
I did not hear the whole explaination on this one, but it had to do with the fact that the sidebands are some number of dB down from the carrier, and if one were to produce a 1500 watt PEP DSB signal, they would have to mix in a 3000 watt carrier in order for it to produce a AM signal that was the equivalent of a 1500 watt PEP SSB signal.

I'm not crazy by some generalizations that are popular in amateur radio circles - for example, an AM carrier is 1/4th the peak envelop power.  It serves as a good "get a handle on it" concept but doesn't do a good job of the complex modulation component of the human voice.

I like the paper put out by Agilent:

http://cp.literature.agilent.com/litweb/pdf/5965-6630E.pdf

There is some good technology coming out for peak power measurements.  In the final analysis, for the sake of this post I'd like to assume the legal limit of 1500 watts PEP, we should be able to use the modern tools at our disposal to satisfy FCC's power monitoring requiements. Modern pulsed radar can no longer be satisfied with measurement techniques performed just a few decades ago and the industry is rising to the occasion.

My approach is fairly simple.  First, I measure my 1500 watt power output developed across a precision 1500 watt load using, yes, the venerable Bird 43 watt meter.  At the same time I'm using a variable coupler to establish a 8 cm envelope display on my  scope ( 50 ohm input on the scope to accomodate the coupler).  Next, I adjust my transmitter (AM or SSB) so that my instantaneous peaks do not exceed the 8 cm level.  The carrier falls where it will - the final requirement from FCC (in my view) is that I never exceed the instantaneous 1500 watt level as established by my fairly simple setup.  At the same time, I can be reasonably assured that I am not flat-topping by observing the scope.

If an AM transmitter is properly adjusted, there will be no observable change in average power during modulation

Al

Hmmm, doesn't add up if they are talking about total sideband power and total AM power equivalencies.

If you're talking about replacing a 1.5kW PEP SSB with an equivalent AM station:

Let's say you're going to replace a 1500 PEP sideband signal with an equivalent AM signal at 100% modulation.

Pt = Pssb, total power is 1500W

Modulation percentage = 100% so modulation Index in formula = 1

Pt = total power in SSB

Pc = carrier power(for AM)

Ps is total AM sideband power

Pt = Pc + Ps; Pc + Ps = carrier plus sideband power for AM

Pt = Total Power = 1.5kW(total power in SSB) =  Pc + 2(1^2)/4)) = Pc + 0.5Pc

Pt = 1.5 Pc

solving for Pc, Pc = Pt/1.5Pc, so Pc = 1.5kW(total power in SSB)/1.5 = 1kW carrier power for AM.

Ps = is Total Power of AM sidebands = Pt - Pc = 1.5kW - 1kW = 500 Watts

Ps = 500 Watts, or 1/3 total Power of combined  Ps + Pc

That sounds like the logic behind Timtron's determination of what the legal AM carrier limit is. I read a book once that said the peak power of an am signal was 4 times the carrier on one page, then on another said that the peak power of a 1 kw carrier at 100% sine wave modulation was 1.5 kw (carrier plus the audio power from the modulator).

If you read that in a book then the book was wrong. The peak power of an AM (DSB with full carrier) is 4x the carrier power at 100 percent modulation. The average power of an AM signal modulated with a sinewave to 100 percent is 1.5x the carrier power. Some AMers want to improperly mix PEP and average powers to claim they can legally run 1 kW carrier and modulate 100%.

Al has the correct approach. Measure 1500 watts carrier with an accurate meter and then set your scope for that level. If your positive modulation peaks never exceed the level on the scope, you will never be running more than 1500 watts peak, no matter the carrier level.

yup.

   I am jealous that Al has that kind of power capability to run a dead 1500 watt carrier. Not many of us can do that. That said E^2/R = W, so it is just a mathematical relationship to run say 375 watts carrier as measured on the watt meter along with X CM of deflection on the scope, and from that calculate where 1500 watts would be on the scope.

Jim
WD5JKO

Now I understand what happened to Al's power transformer. ;D

oops, I found a mistake in that post. The book was quoting input power, not output. It said the modulator causes the plate voltage and plate current to double, which would make the power go up 4 times (2000v .5A under modulation would be 4000v 1A). On the other page it said the total power input to the final in a kw input transmitter would be 1.5 kw, 1 kw of DC and 500w audio. But the same book also says that the input may not really be 4 times exactly at 100% modulation, because the plate voltage and current are not both going to double. It says the plate voltage may double, but the current might not quite double.

At no time did I ever run the AL82 such that it exceeded specification. The transformer should have not failed.

If my comments were carefully read, it would be seen that my 8 cm scope setting was based on a measured 1500 watt level using a Bird 43 and terminated in a precision load - not based on any other assumptions

Power is ultimately measured based on the scientific fact that both DC and RF when properly dissipated, generate the same amount of heat.  When this heat is accurately measured the RF (or DC) power can be accurately determined.  I have used this calorimetric technique during high power radar transmissions.  In that application, the actual rise in water temperature is measured against a measured flow rate / volume. NIST (National Institute of Standards and Technology) uses this method to establish a national standard for accurate power measurements.  I offer one page from Agilent's paper (not copyrighted) that shows how NIST establishes these standards.

If one is running much less power than legal limit, the requirement for my previously posted technique or its equivalent is not necessary, in my view.  It is then only necessary to have some sort of power measuring equipment that will give a general idea that the transmitter is "healthy."  It is, however, necessary to know that the transmitter is properly adjusted so that excessive  bandwidth does not occur.  I think a scope is essential for that monitoring.

Actually, I think we may be a bit off topic.  As I understand the question, how does the average power compare of AM and SSB stations outputting 1500 watts PEP?  

With an AM signal modulated 100% equally in both the positive and negative directions, the average power as read on a meter should be equal to the carrier power, only when you start to get some assymetrical modulation would the meter start to move upward or downward.

So from this statement I said:


 I didn't suggest Al that you were running over 1500 watts; just stating that many of us cannot make 1500 watts carrier with our stations. I can do 1500 PEP, but no more than 1100 watts carrier due to poor line voltage regulation.

 The comment I said about the power transformer was uncalled for, and I'm sorry if that offended you. It was a joke in poor taste.



Noted, but those Birds are good for +/- 5% accuracy usually and that is full scale. So to measure 1500 watts with a Bird 43 don't you need a 3KW slug (or is it 2500 watts?). Point here is the Bird could have been more than 5% off and still be within specification for a near mid scale reading. Most dummy loads see a shift in the 50 ohm resistance from a huge thermal load. I see that at work with the big 5KW Bird load with the cooling fans. The measured power drops about 5% after 60 minutes at 3KW (13.56 Mhz). The point here is getting an accurate power measurement to 5% or better is tricky for a carrier, and even trickier for repeatable PEP measurements.


Still if we run AM or SSB and we exceed 1500 watts PEP occasionally, and for brief intervals, who would know, or who would care? Someone else running half the PEP could sound louder when using audio processing.

Jim
WD5JKO

If the FCC shows up at your door, it's pretty likely they will use a Bird too.  :)  No worries.

There no longer are any power monitoring requirements in Part 97. It used to be a rule that if the DC input exceeded 900 watts, "accurate measuring instruments" were required to monitor input power.  When the p.e.p. bull-crap came out, the FCC, aware that the average Joe Bloe Hammy Hambone wouldn't  have a clue how to accurately measure p.e.p. output, let alone possess the necessary instrumentation, deleted the requirement altogether.  In their docket proceeding, they stated that amateurs could use other means besides accurate measurement, to determine power output.  Now try to figure that one out.

An SSB transmitter sends no carrier (or at least a 50 dB down carrier), so the carrier power is essentially zero.

A given SSB transmitter is said to have the same communication effectiveness as a conventional AM unit running much more power. For example, a 100-W SSB transmitter supposedly offers the performance capabilities of an AM transmitter running a total of 400 W, since they both show 100 W of power in one sideband. The supposed power advantage then, of SSB over AM is 4:1.

The only other advantages stated for SSB over AM is occupied spectrum and lower noise inder the same conditions.

But then again, SSB ain't 1/4 the fun as A3E.   ;D

Phil - AC0OB

The carrier 1/4 peak convention comes about from the practice of using a sine or other symmetrical wave for tests. If it swings equally both ways, that's what it will do. My unprocessed voice is on average fairly symmetrical. It is different for every person and voice and for each lash-up. It is even different depending on what is said, such as vowels etc.

It's possible the plate modulated TX was mis-adjusted or malfunctioning during those observations. Could have been running a slightly low carrier, leaving the modulator headroom to go above 100% positive.

I don't like the conventions/old wifes tales etc either but a test with voice or a defined wave that others can duplicate is a good place to start.

If that is correct, then I think the expectation is that an operator would make an honest effort such as using a scope to compare peak voltage to a known voltage. Many scopes in ham hands are definitely in the "other means besides accurate measurement" category so it fits the rule.

What do you think they really want us to do?

and on the receiving end - the formula applies there too against bandwidth vs noise and signal doesn't it?

so it is 4* more, * 4 times more. The real advantage seems to be 16*.

Maybe just putting your hand on the tank coil would be enough of a "other means" of measurement.

An old engineer at a radio station once showed me his power measurement system...the line voltage meter went down when it was putting out the right stuff...

73DG

This depends on what the meter is measuring.

For +/- 100% DSB, full carrier AM by a sine wave, a thermocouple r-f ammeter in series with the antenna/load shows a current increase of SQRT(1.5) = 1.225 X (assuming the value of the load impedance is a constant).

AM broadcast stations commonly modulate to nearly 100% negative and 125% positive peaks

The jpg linked below shows peak values for various amount of asymmetric AM.

Of interest is that the peak power is a function of load SWR -- which introduces another dimension into this for ham  operators who need to observe a PEP limit.

That's right! When my desk lamp drops 1000 lumens I'm WorlWide!

Ok, the only part I don't understand is at the top it says the unmodulated carrier is 187.5 watts, but in the chart gives the peak power as 375 watts at 0% mod, and 1500 watts for 100% and that's in a 50 ohm load with 1:1 VSWR. so going by that chart 187.5 watts carrier is 1500 watts PEP.

And second, going by the FCC's own rules, how could they cite someone for running over 1500 watts PEP if they don't have to measure it accurately?

The rule of 4:1 should apply the other way around as well, IMHO. I think we have been brainwashed about the 375 Watt carrier limitation.

The previous set of math only showed the Total (average) power equivalency between an AM and SSB signal.

If an SSB signal is 1500 PEP (which is an "average" power for the peak of an RF waveform fully modulated), and which is only ONE sideband, then AMers should be allowed to generate an A3E signal which has the same sideband power. That is, in order to produce an equivalent signal which contains a sideband power in one of the sidebands of 1500 Watts, then working from bottom to top this time:

1500 watts sideband power in one sideband is 3kW total for two sidebands.

So for 100% modulation, I really need a transmitter with a total power output budget of 6kW.

power budget by category is:

Pc = carrier alone = 3kW

Psb = 3kW for both sidebands

Plsb = Pusb = 1.5kW sideband power.

Maybe this is to what Timtron was referring.  ???

P.S. I will be happy to accept the old 1kW power input, unmodulated, final stage power rating.  :D

Phil - AC0OB

Hi Don.  Yup, that's the reason for my careful "...for the sake of this post..." wording.  Surely the FCC is aware of the implications of their changes in Part 97 and would not get into a complicated dialogue with the amateur community on the traditional ham bands regarding this question.  I’d like to limit my comments in this excellent thread the betterment of our state-of-the-art measurement techniques.

It’s my wish that we all seek good engineering in the amplitude modulation mode so that it is an enjoyable and uplifting experience.  We are the AM family and should always be looking for ways to improve our family. That would include, in my view, a well tutored family of AM’ers who know how to keep their stations in good operating status.

Al

It seems to me a lot of this 'concern' is misplaced, or even groundless (no pun intended).

My neighbor Roy had a 6-tower array hioldi9ng up a Steber curtain.  Fed it with OWL on 20m SSB, from a single 4-1000 linear.  His field strength was phenomenal, as one would expect. 

Suppose an FCC agent with one of their newfangled Tahoes set in the beam of that curtain and tried to estimate his TPO?  What could they possibly use as a benchmark?

Again, how would they make a determination without extensive testing on site with calorimeters, FS meters, input measurements, bigass budget, eTc?

Roy using a simple dipole would have a lot different result, with the same power input.

Boys, the bottom line is if nobody complains to them, they won't be at your QTH. 

That doesn't mean one has carte blanche to do as you wish, but decent use of the bands is your passport to good hamdom freedom.

A crappy 50-Watt splatter-box will get you a visit a lot quicker than a smooth 5kW into a solid antenna.

73DG

You're assuming the comm authority now has knowledgable people who have had radio communications engineering and mathematics somewhere in their training.

Back to measurement. From all of the reading I have done, measurement appears to be a "scope-and-calculate" methodology.

But then, do I measure on my voice or someone else's voice, or do I put in a two-tone signal (at what two frequencies?) and adjust my equipment so my scoped signal is 1500 Watts average power on RF peaks, and at what impedance? Theoretically, I could use any impedance since the definition for PEP = V^2rms/R(z).

I think this is why Part 97 is vague and maybe it should stay that way.

Phil - AC0OB

To me, the number one consideration, regardless of mode and operating power used, is to maintain a CLEAN signal with (in the case of phone operation) good, undistorted audio quality.

Here's how the feecee shot themselves in the foot by adopting the p.e.p. garbage rather than using average power for their output standard, at least regarding SSB.  Under the old DC input rule, one could legally run as much peak power as one could generate, as  long as the DC input remained under 1 kw.  Although there are other variables involved, average output power is at least an indirect function of DC input power, with a given transmitter under given operating conditions.  That means one could run as much peak output power as one wanted, as long as the average power doesn't exceed a certain limit - and it is average power, not the power developed on occasional voice peaks, that determines the loudness and interference-causing potential of a transmitted signal. 

Under the original rule, one could run a peak SSB power as much as 14 dB (using Steve's figure) above the average output power limit and remain legal (this would apply equally well to DC input as to average output power). The signal would attain high peaks, but the average power level would still fall within the limits and therefore the signal would not produce undue interference due to its loudness, and the signal would be clean and undistorted if good engineering practice were used in generating the SSB signal, including operating the linear within its undistorted output capability. OTOH, trying to stay within a p.e.p. limit encourages heavy processing or simply overdriving the linear to get the average power (and thus the loudness of the signal) up high, while keeping the peaks under a  certain limit.

Under the old rule, a clean unprocessed signal could be maintained within the legal limit by running as high a plate voltage on the final amplifier tube as practicable, to allow plenty of head room, but the peak-to-average ratio of the human voice would keep the average DC input, and thus the average power output, within the specified limit despite the high amplitude that would occur on instantaneous voice peaks. Run the signal level required to hit the maximum DC input or average power output on your loudest voice syllables, let the peaks go where they may, and make sure the amplifier and exciter don't flat-top up to and slightly beyond the point of the highest voice peak.

The limitation on p.e.p. encourages broad, crappy-sounding SSB signals. If the signal is kept clean with little processing, the p.e.p. rule actually reduced SSB power as much as, if not more than, the alleged AM power reduction.


The same goes for bandwidth limitations.  Riley said as much a few years ago at one of the Dayton FCC forums.

97.3, (b)(6) PEP (peak envelope power). The average power supplied to the antenna transmission line by a transmitter during one RF cycle at the crest of the modulation envelope taken under normal operating conditions.

Yes P.E.P. Is an AVERAGE measurement by Part 97 definition.

It basically says the highest average power measured at the peak of one cycle of the carrier during modulation.
"Normal operating conditions" means this highest power being transmitted while YOU are operating in YOUR normal manner.

That's not hard to understand.

Not hard to understand?

Well, saying "highest average power measured at the peak of one cycle"
is hard for me to understand.

The highest "average" measured at the "peak" sound like double talk to me.

Peak of what?  Or do they mean "crest? of an RF cycle? A single crest of an RF cycle would not allow enough time for heating of a thermocouple to accurately measure power, since a thermocouple has a thermodynamic lag or thermal "time constant."

This is why I say it's a scope measurement-calculate thingy.

Phil - AC0OB

Hey, it's the definition we have to work with.

If you have a decent peak reading wattmeter you'll probably be fine ifn the G men come knocking!

I would like to see when the last time the FCC actualy took action against a ham for excessive power output. That was interfearing with people or causing problems.

"The average power supplied to the antenna transmission line by a transmitter during one RF cycle at the crest of the modulation envelope taken under normal operating conditions."

Get out the 5Gs/S scope and capture that one cycle!

There are all kinds of ways to present math and graphical arguments to express opinions about the "average" of the area under the one cycle curve. It was even 'proved' the power was zero at all times if there was no modulation.

The discussion about that rule and measurements has been disemboweled and beaten to death about 2 years ago. Now the dry bones will be ground.

http://amfone.net/Amforum/index.php?topic=25835.0
http://amfone.net/Amforum/index.php?topic=20087.0

http://amfone.net/Amforum/index.php?topic=3670.0 was good too

People new to AMing (and it seems more are coming on board to it) will be wanting answers/opinions to this question for some time to come.

Don and Timtron's comments are right on according to the math in this thread:

http://amfone.net/Amforum/index.php?topic=20087.0

Phil - AC0OB

It is simple. Find the peak of the RF envelope (or the crest is you prefer that terminology), take one cycle of the RF portion and calculate the average power of that cycle. Using a scope is a good way to make the measurement and it allows you to easily visualize what is going on. In the attached scope image, you would make the measurement of the one RF cycle at the point marked by the red arrow. This would be the maximum PEP for the time shown on the scope. Most PEP meters have a time constant, so really the PEP shown is for a given time.

What he is saying, is that when 1 kw of carrier is modulated 100%, the additional power in the sidebands is 500w peak power.  Peak power, because it occurs only at 100% modulation.  Most of the time, with the average human voice, the modulation percentage is more like 30%.  So 1000 watts carrier + 500 watts peak sideband power = 1500 watts total peak power.

97.3, (b)(6) PEP (peak envelope power). The average power supplied to the antenna transmission line by a transmitter during one RF cycle at the crest of the modulation envelope taken under normal operating conditions.

That would mean that an AM signal consists of a carrier that varies in amplitude with the modulation.  We have known for decades that this is not the case. An AM signal consists of a steady, unvarying carrier, plus the upper sideband and lower sideband off to the sides of the carrier.  This is clearly visible on a spectrum analyser. You see the carrier which extends way up to the highest point on the display.  To each side, you see the sidebands, each of whose peak amplitude extends up to a maximum of 50% of the carrier voltage, which equals 25% of the carrier power. There is no "rf cycle" that has an average power greater than that of the dead carrier over any portion of the modulation cycle. What the scope's envelope pattern shows is the total power, the sum of the independent carrier plus two independent sidebands. If the total sum of the power of each sideband plus the carrier is the limiting factor, then W1AW is violating the power rule with their bulletin simulcast on multiple bands, since the sum of the total power they are running on all of the multiple frequencies added together exceeds the so-called "legal limit". This goes back to the 1920s debate over the physical reality of sidebands (http://amfone.net/Amforum/index.php?topic=26633.0).


If the carrier is modulated 100% on voice peaks, then at each peak the sideband power is exactly 1/2 the carrier power. That means the total power is 1.5 times the carrier power at voice peaks.


What they are saying is that the final amplifier may not have perfect modulation linearity.  With perfect linearity, if the voltage is doubled, the current is also doubled.  This is true with both input power and output power.  The question is, is that 4X power all in one rf cycle, or is it the sum of one cycle of carrier, plus the sum of one cycle of all the signal components of each sideband added together.

The comment about W1AW reminded me of something I thought of the other day. what if you took a transmitter, split the ouput in two, then fed the two signals into two seperate linears, which fed two seperate antennas in a way so that both where in phase. say both linears put out the legal limit by themselves. so in theory, the effective power being put out would be twice the legal limit, but technically should be legal, since no where that I have found does it say that you can't have more than one transmitter in operate at once. it would kinda work like the synchronous AM stations that are in some places.

Not really. The spectrum analyzer displays average power or voltage. Use a realtime spectrum analyzer and you will see the carrier vary in amplitude.




Partially true. A scope displays voltage, not power. And if you change the scope's time base and you will see a single sinewave at the carrier frequency and the amplitude will vary.

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?

Spectrum Analyzer wise (frequency domain wise), as modulation percentage increases, does the carrier start to dissapear in order to put power into the sidebands, or is power placed into the sidebands and the carrier remains steady:

http://www.williamson-labs.com/480_am.htm

Update: consider the basic total AM power expression where Pt = Pc + 0.5*m^2*Pc; The only part that varies is the sideband power(second term), and not the carrier power, carrier power is constant.

Phil - AC0OB

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 suspect if the FCC ever came down on a rich HAM and the operator decided to take the FCC to court, a smart lawyer could make the FCC look stupid for such a confusing reguation.

There seems to be as many interpretations of the rules as there are people responding to this thread.

I'm more confused that I was before I read this thread.

Since I can't put up a visible antenna in my CC&R-bound subdivision, none of my neighbors even need to know I'm a ham, so I figure no complaints are likely.

Jackpot!  Or to put it another way, this is why I just fire up the rig, get a carrier going around 300+ watts, modulate it and don't worry.  What I do worry about is where the audio rolls off on the high end, the leen-yar being linear, and the carrier not getting clipped off. 

 

New game "Find the Ant!"     Finding the tower doesn't count.  ;D  Now if we could come up with an invisible sky hook. . . . .

What about that tree line to the west of your QTH.  Might there be a possibility?  Or you could set up a remote using a Flex + linear and you would be a tall ship.  Looks like a back yard to me  ;D  Under the cover of darkness (COD) you could run a coax to the base of a tree and go from there

Al

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.

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.

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.

Which proves my point.

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

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

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..

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.

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.

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.

Only those who are duly deputized.

(http://www.maxarmory.com/images/products/hr73.jpg)

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

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.  :)

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  ;D  ;D

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.


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

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

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."    ;D



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

Phil - AC0OB
  

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.

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

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? ?   ???  ???  ;D  ;D

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

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.  

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"

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.

Works for me.   ;D

I think if you run a clean ship and are courteous to other opereators, the FCC doesn't care about your AM intrepretation of the Part 97 power subparagraph.

Phil - AC0OB

I prefer to paraphrase it to "Strap softly and turn up the wick".

But that doesn't translate to the bogus practice I have heard a few mention, of running 750w of carrier and keeping the modulation low enough so that their Hammy Hambone meter doesn't kick above 1500.  Although, with most voices, phasing the audio the wrong way at 1 KW DC input will likely cause that meter to peak right at 1500 when the negative modulation hits 100%

Here's the latest suggestion someone sent me to add to the Phony Operator list:

You might be a phony operator if you obsess about running precisely 375 watts, or ask if anyone manufactures a 375 watt rig.

There's a big difference between guys saying they run a 375W carrier for the sake of discussion of general settings and those who believe that is a requirement or actually do it. I'd say cut them some slack because they are recognizing the rules as they themselves understand it.

Your phony operator who thinks he is getting a real 375w/1500W amplifier will probably be disappointed when he cracks the book and finds out how he's been robbed in the duty cycle department. hehe 10 minutes plate time, 30 minutes standby..

High-carrier with downward modulation looks on paper like it makes the exact same output waveform result in the diode detector as running a low carrier and using ultramodulation to hit 1500W peaks. Except that the receiver AGC does not go as crazy. The speech wave is inverted but that is only speaker phase and does not matter for listening.

Before the high carrier is dismissed, check the transmitting tube manuals for the words "modulation essentially negative". No one has really answered what/why that was done. Military reasons? Everyone knows the 833. It was brought up before in a tube discussion but IIRC no one remembers why it was in the handbooks.

How would one build a transmitter that modulated only downward? Besides inverting the speech, probably have to have some kind of positive peak limiting?

Here's what I was thinking about this morning. Going by the sidebands are 4 times the carrier idea, that would mean that the sidebands are +6dB to to the carrier, when in reality, the sidebands together are -3dB to the carrier, making a single sideband -6dB. If the sidebands were really stronger, then when listening to a really weak station, you should be able to hear the sidebands but no carrier. But, it is more likely that you can detect a carrier than you can the sidebands. That's part of the reasoning behind running more audio power so that your modulation is over 100%. For example, say we have an upside down tube transmitter. We feed 100 watts of audio in and get 75 watts DSB out (not applying plate voltage yet). Now, we apply the plate voltage for 25 watts input and get 18.75 watts carrier out. Sidebands are 4 times the carrier, right? Now we compare this to a regular plate modulated transmitter that is also running 18.75 watts of output. Sidebands should also be 75 watts PEP. But the actual audio power in the sidebands will only be 9.375 watts. Now which one sounds better on a receiver. Sure, the carrier to sideband ratio is supposedly the same, but the plate modulated transmitter is gonna sound a lot better than the upside down tube transmitter when received on a conventional AM receiver. The upside down tube rig is gonna sound way overmodulated, because it would have more audio power.

You don't have to  do anything to the audio, if the speech amplifier and modulator are reasonably distortion free and have good phase-shift characteristics, particularly towards the low end of the audio spectrum.  Most voices are naturally asymmetrical.  Just make sure the polarity of the audio line feeding the modulator is phased the direction you want it.

As far as interference-generating potential of the signal is concerned, I can see no reason why a 750 watt carrier modulated 100% negative and 50% positive would cause any less interference than one modulated 100% positive and 50% negative for full peak output; you still have the same sideband power.  The advantage of phasing the dominant peaks to the positive direction is that you can modulate 100% negative and well above 100% positive, if the transmitter has the head-room.  This increases the total sideband power for a given carrier power. 

In any case, the carrier should not shift upwards or downwards during modulation.  When running AM linear, particularly if you are handicapped by marginal plate dissipation and/or power supply capability, phasing the dominant peaks in the downward direction to 100% might actually be advantageous, since the resting carrier efficiency could be substantially increased without driving the amplifier to flat-topping on modulation peaks, allowing more carrier output for a given DC input and tube plate dissipation.  This would allow for greater total sideband power, plus more carrier power to suppress the background noise.

Forum readers may be interested in the paper linked below, relating to power-saving modulation techniques available on newer AM broadcast transmitters.

It is not the "controlled carrier" approach that was used in the Heathkit DX-35, etc.

http://radioworld.com/article/mendenhall-expands-on-mdcl-discussion/211748

So all you would have to do is determine which direction your voice is asymmetrical towards (positive or negative), then adjust the phase so that it goes more negative than positive. With a plate modulated rig, this can be done pretty easily just by reversing the leads on the mod iron's primary (if side A connects to tube A, and side B connects to tube B, then switch it so that side A goes to tube B, and side B goes to tube A). But the problem with running high carrier with high percentages of negative modulation would be you would need a tube with higher power handling capabilities to be able to produce the amount of carrier you want, but the tube would actually probably run about as cool as the same tube would in a linear amplifier, since the power would actually be dropping on peaks, instead of increasing, you wouldn't have tubes with glowing plates like you would with a normal plate modulated transmitter.

IMHO, this is best done in software such as SDR. SDR processing is usually part of the AM Companding system.

For example, analog audio or digital data comes in and is converted or stored for pickup respectively by the Digital Processing System. DPS subsystem examines the present waveform it has just outputted, and waveform just stored, and makes a feedforward prediction based on an algorithm.

The output might be a data word previously stored in a look-up table or the output of the algorithm, which then controls Carrier Power and Modulation Index.

Phil - AC0OB

That's the $25 question.
CBers do it by overdriving everything but that's a poor answer.


My comment took into account all possible methods of making that signal including high level or whatever other weirdness could be imagined. so as with splatter, there is danger of interference if the amplifier is clipping.

Exactly!

Ive no interest in LOSING rights that I had as far back as the late 50's and run what I damn well please within those regs that I personally consider grandfathered.

Now, let some snot nose whiner on here send THAT to Charlie.

The idea would be to rig the transmitter to act kinda like a backwards balanced modulator. A normal balanced modulator would cancel out the carrier and leave just the positive peaks (double sideband suppressed carrier). The "backwards" balanced modulator would leave the carrier, but transmit negative peaks. Or another possible way of doing it that I can think of is to somehow build a modulator that runs on a negative voltage, but run the final on a positive voltage. I could see this possibly being done with a class D/E rig and PWM modulator, but the modulator would be running on negative voltage. So you would run the final at the normal positive voltage. As the modulator drove the final more negative, it would reduce the positive voltage to the final, which would increase the negative peaks. If the modulator had a positive peak limiter, then you adjust that to limit the positive peaks to whatever you like.

My sentiments exactly.

So now your "Maserati" that you once could legally floor is now stuck in third gear if one is to abide by the revised rules that would allegedly reduce the maximum output for AM. While I don't condone illegal amateur radio operation, if the rules you have lived with all your life are fraudulently changed on you to your disadvantage, how apt would you be to respect them?

It can be frustrating, do what you think is right. For my friend in the tiny Republic of Vinco, there was never any real question as their privileges were (and are) a little freer.It's a shame we don't have reciprocal privileges with them but the Canadians have a pretty good thing.