QST AM Article and SSB Power

[k4kyv]

The article "Why Not Give AM a Try" that appeared in February QST (p. 43) points out a not-so-well-known fact that will undoubtedly be overlooked by most readers.

Power level

Your 100 W SSB transceiver puts out 100 W PEP on SSB.  That is, at the peak of your voice envelope the  power output is 100 W, just as it can be 100 W with your key down on CW.  When you're not talking on SSB, your power output is 0 W.  The actual average output is typically less than 10W, depending on voice characteristics.

Of course, this is in reference to a good quality SSB voice signal that is not over-driving the rig or linear amp, and is not overly processed.

At the 10w level, on an amplifier capable of 100 watts peak, the amplitude of the signal voltage is running at just 31.6% of the amplifier's peak capability.  The amplifier is running at 1/10 of its peak power capability, and since power is a function of the square of signal voltage, the output voltage is 1/√10= 1/3.1623 = .316 or 31.6% of the peak voltage capability.

If you ever watched the analogue VU meters at a recording studio or broadcast station, you might have noticed that when a person is talking, the meter hovers at about the -10 VU or 30% modulation level, even though it may kick up towards 0 VU (100% modulation) on occasional peaks.  With music and other program material, it may run much higher.

So, the average power output level of a linear amplifier running SSB is actually less than the unmodulated carrier power of that same amplifier running AM at the same peak power level, and the SSB efficiency is averaging considerably less than when the amplifier is running AM.  The difference is not so obvious, because with AM, the carrier operates at a continuous 100% duty cycle, while with SSB, the power output is intermittent, running at a very low duty cycle, but the meters kick up to maximum on voice peaks while the meter stands still when the amplifier is operated properly on AM.

So much for the alleged "inefficiency" of a linear amplifier when it is used to run AM.

This means that at 1500 watts pep output, the average output power of a SSB transmitter should not exceed about 150 watts.

Therefore, the p.e.p. power limit bullshit penalised SSB just as much or even more so than it did AM, assuming that the SSB transmitter is run cleanly and properly.  Under the old DC input rule, a linear could be run up to where the meters indicated a kilowatt DC average input, with the peaks allowed to go as high as the headroom of the amplifier permitted. Amplifiers in the 50's-70's were universally touted in the ads as capable of "2000 watts pep input".  By running the linear at higher peak power, the clean SSB output power could be legally run considerably higher than it can under the present rules.

How many of the slopbucket linears you hear on the air these days are really operated within that power limitation?

Now, explain that to the next slopbucketeer you hear pissing 'n moaning that AM'ers run "illegal power".  

(Unfortunately, the concept will probably go right over his thick head.)

[Opcom]

SSB makes up alot of deficiencies with the apparent increase in loudness at the other end, but half of that seems to be in the receiver.

There are many places in the older HB and other weighty tomes where the SSB voice wave is shown, and it is remarked that the avg power is 10% or so. Much is made of this, in an attempt to educate the SSB user that it is not the goal to merely crank out as much power as possible, but rather, go easy on it (if no kompressor is present) to avoid distortion.

So, since the PEP BS penalized SSB, the users of that mode would be well-served to work to get the KW DC rating back. But I think the FCC will never allow increased power. The PW/QRP horse is out of the barn. And like you say Don the slopbucket preferrers won't see the merits.

Operators did, and still do their best to make the most of the limits regardless of kind.

DC rating: increase PEP as much as possible.
AMers used to go way positive on peaks.
SSBers had free reign pretty much.
No one had to count drive watts going to a GG amp, or did they?

PEP rating: increase average power as much as possible.
AMers can boost the carrier and modulate downwards by inverting the speech waveform (up to a point)
SSBers just compress and compress.

Hey at least the FCC does not make us use "wall plug power" as a standard.

[K5UJ]

I think more hams are going to run QRO, at least for phone.  They will be driven to it by the number of RFI spewing appliances out there raising the noise level and making reception of <= 100 w. rigs with average antennas impossible.  I don't know anything about these qrp weak sig. modes -- maybe they can get through somehow.  We pretty much can't control all the garbage unfiltered gadgets out there, a lot like me can't afford to move to the country, and separate rx antennas and noise canceling boxes only go so far.   The one thing we can do, is up our tx power and antennas.  The new S3 is now S9.

Unfortunately, 10 % av. power only serves to make SSB ops run out and buy these speech processors, the latest being sold by Ten Tec, who's ad claims "almost 6 dB" increase in power.  I'm sure 8 out of 10 buyers will be ops who run these things with all knobs fully clockwise and of course they don't use scopes and have average reading watt meters.  Just wait until a lot of them buy that Ameritron solid state 1.2 kw amp.  It's all a recipe for unintelligibility, fan and saliva sounds.   

Rob

[KX5JT]

Darth Vader on steroids!

[N2DTS]

I doubt many operators limit power output no matter what mode they use.
I suspect the real power limit is what the station can run somewhat cleanly.

Taking the tube lineups of AM rigs and ssb amps I hear people using, I seriously doubt everyone is running their stuff at 20% power all the time.

Has anyone ever heard of anyone getting busted for running excess power if it was not something like 15,000 watts pep?

MY personal power limit is likely driven by the qrm I can generate in the hood, I don't want a big angry mob with pitchforks and torches outside the house....

I suspect the only people who really watch the power output are those running fragile expensive collectors items like the KW1...I bet no one straps one of those rigs anymore!

Brett

[k4kyv]

Brett and Rob, what you say is made even more salient by the fact that the FeeCee deleted the rule that used to require amateurs to possess accurate means for measuring transmitter power.

The old rule required accurate measuring instruments whenever the nominal DC input power exceeded 900 watts.  Johnston and his Private Radio Bureau crew knew full well that accurately measuring RF output power, especially peak power from SSB transmitters, would be beyond the means of many if not most amateurs, due to lack of appropriate measuring instruments and lack of knowledge of how to use them.  So, in the R & O of the power limit change, they made the incredible statement that (to paraphrase the exact wording) "amateurs may use means other than accurate measurement to determine their output power", and "amateurs are not required to measure their output power; they are merely required to comply with the rule".

And remember, this was written in 1983, when the overall technical expertise of the amateur radio community was at a substantially higher level than it is to-day, and just before the FCC moved amateur radio enforcement to near the bottom of their priority list.

[K1JJ]

On average vs: peak power for AM or SSB:

When I have an SSB pileup calling from Europe, assuming many guys are near the same strength, I usually hear the ones with the cleanest audio first. The ones with the processors (higher average audio with more distortion) and high pitched audio seem to blend in with each other. I've been an advocate of running NO processing and 2.8kc audio on ssb for a long time. But most do the opposite, of course, to get that last average watt out.

The strangest thing is that the boomy ESSB guys seem to stand out the most and get picked out easily. Proabaly cuz they are the only ones with the bassy voice tones to hear and everyone else sounds like white noise when combined.

The same goes for receiving. We need the cleanest receiver audio we can get to hear the weak ones. Obviously, any distortion detracts from the intelligibility.

On transmit, I watch my PEAK reading wattmeter. An AVERAGE reading wattmeter will hover much lower and cause us to have bad habits like overdriving the audio in many "clever" ways related to speaking.  I dont care if my average power is 10% or less, if that's what it takes for clean audio and intelligibilty. That's what counts to me. If the S meter is set on "fast," it will respond better to peaks anyway. That's the way I run it to keep the game-playing low.

Lately, I've been experimenting with breaking my ssb transmit audio into 6 bands.  No RF processing, just audio processing. We'll see how that works out soon.

On AM I prefer to do the opposite and run a higher density audio.  Most of the power is "wasted" on a carrier and a second sideband, so we need all the help we can get on AM.  But the same rules as above apply to AM - the cleaner the audio, the easier it will be to get through and be understood during marginal conditions.


T

[Bill, KD0HG]

For what it's worth:

I had a mail go-around with a deputy in Johnston's office when the power rules were changed back then.

He told me, "We're not going to endanger the safety of our field and enforcement people by having them attach meters to high voltage in a ham's equipment. We have peak reading wattmeters and that's the way we're going to do it from now on."

OK..

And then, there was the issue of people running the legal 1 KW DC input on AM and then running 400% positive peak modulation. Even the sidebanders were starting to figure that trick out..Run 10 KW PEP on sideband and inject 50 watts of carrier...It's still "AM" and 100 watts DC input, right? Turn that mic off and the meters are gonna read 100 watts DC input every time.

No wonder they changed the rule on power measurement. But this is a different issue than cutting AM back to 1,500 watts PEP, or 375 watts of 100% modulated carrier. They could have raised the legal limit to 3KW to 4 KW PEP for everyone, at the time, instead of disenfranchising AM.


Bill

[k4kyv]

Average rf power output would have adequately covered both of the FCC's issues.  

Undoubtedly, this was initially provoked by the W3PHL case in the late 50's.  But it took the FCC over 25 years before they decided it was a significant problem.

They managed to come up with satisfactory rules in Canada, that didn't reduce anyone's privileges.

But, I forgot.  Canadians are smarter than United States-ese.

[k4kyv]

And then, there was the issue of people running the legal 1 KW DC input on AM and then running 400% positive peak modulation. Even the sidebanders were starting to figure that trick out..Run 10 KW PEP on sideband and inject 50 watts of carrier...It's still "AM" and 100 watts DC input, right?

How could that possibly work with SSB?  It did work with plate modulated AM because the average voltage of the modulation, consisting of unrectified alternating current, reads zero with a DC meter, and when superimposed on the DC from a power supply and read with a DC meter, only the DC voltage and current registers on the meter. With SSB, even with injected carrier, the DC input to the linear would still have increased tremendously when modulation was applied. W3PHL did it using double sideband, by running about 600 watts carrier with a slightly unbalanced high level balanced modulator, and applying 5 kw of audio as plate modulation.

[WD8BIL]

I only use the power level necessary to maintain reliable contact.

'Course that takes into account the slopbucket, carrier, swisher and hola hola interference on any given night.

[K5UJ]

<<I only use the power level necessary to maintain reliable contact.>>

Same here Bud, and my contacts are  very very  reliable, or as reliable as I can make them 

[Bill, KD0HG]

Here's the way I'm looking at it, Don.

The old rule was 1 KW DC input. Amps x volts, CW, no audio. Didn't matter is you were running CW, AM, FM or RTTY. There were no specifications as to how much your plate current could rise under modulation. There were no rules for maximum permissible positive modulation, either.

The FCC would have you key the transmitter and they'd read amps x volts on DC meters.

There was also no regulation concerning how much positive peak modulation you could run, OTOH, exceed -100% and you splatter, not 'Good Amateur Practice'.

If you had an SSB station, they'd have you transmit a CW carrier and read volts x amps on the final. They didn't measure your PEP. In fact, those running 50% efficient linear amplifiers were getting a worse deal than those running more efficient Class C.

So in my opinion, under the old rules, you could legally run 10 KW of sideband power (DSB or SSB) with a 50 watt carrier under CW conditions and be legal. All they read was your steady state power, NOT with any modulation applied. They never asked you to whistle into the mic while measuring DC input power, did they?

AM broadcasters had a different set of rules, you measured the antenna feedpoint impedance and you measured your RF current with a dead carrier to calculate your RF power. They never measured the RF current under modulation, the 120% max rule came along later. Couldn't do that with hams since we QSY and antenna Z is all over the place.

Remember the articles in the AM PX about how PEP was going to be measured if you were using open-wire feeders? LOL

That's my crack at it, but it's all a moot point now. ;-)

[N2DTS]

And don't forget, they are much happier then we are!

Sounding good last nite Don...

Brett

They managed to come up with satisfactory rules in Canada, that didn't reduce anyone's privileges.

But, I forgot.  Canadians are smarter than United States-ese.

[KB5MD]

When I start modulating the shack lights I know it's turned up too high.  Time to reduce power. 

[W2XR]

Here's the way I'm looking at it, Don.

The old rule was 1 KW DC input. Amps x volts, CW, no audio. Didn't matter is you were running CW, AM, FM or RTTY. There were no specifications as to how much your plate current could rise under modulation. There were no rules for maximum permissible positive modulation, either.

The FCC would have you key the transmitter and they'd read amps x volts on DC meters.

There was also no regulation concerning how much positive peak modulation you could run, OTOH, exceed -100% and you splatter, not 'Good Amateur Practice'.

If you had an SSB station, they'd have you transmit a CW carrier and read volts x amps on the final. They didn't measure your PEP. In fact, those running 50% efficient linear amplifiers were getting a worse deal than those running more efficient Class C.

So in my opinion, under the old rules, you could legally run 10 KW of sideband power (DSB or SSB) with a 50 watt carrier under CW conditions and be legal. All they read was your steady state power, NOT with any modulation applied. They never asked you to whistle into the mic while measuring DC input power, did they?

AM broadcasters had a different set of rules, you measured the antenna feedpoint impedance and you measured your RF current with a dead carrier to calculate your RF power. They never measured the RF current under modulation, the 120% max rule came along later. Couldn't do that with hams since we QSY and antenna Z is all over the place.

Remember the articles in the AM PX about how PEP was going to be measured if you were using open-wire feeders? LOL

That's my crack at it, but it's all a moot point now. ;-)

Sounds to me like it's high time for a test case before the Commission. Anyone care to be the plaintiff in this class-action suit?

We can call Bill and Don/KYV as expert witnesses for the class.

Probably the best solution is to just run what you want within reason and be done with it. My informed feeling is that nearly everyone has been doing that for the last 20 years or so, at least since the new power regulations went into effect.

And Brett, I'm fairly certain that the majority of the guys running the KW-1s, Johnson Desktop Kilowatts, TMC GPT-750s, converted AM broadcast rigs, etc.,  think along the same lines.

Although it is interesting to debate the power ruling on a technical basis, it really is a dead horse issue at this point, with probably zero possibility of reversal or reconsideration by the Commission.

73,

Bruce

[Bill, KD0HG]

I like practical comments like yours, Bruce. The FCC has bigger fish to fry than the occasional QRO ham operator..As it should be.

[W2XR]

I like practical comments like yours, Bruce. The FCC has bigger fish to fry than the occasional QRO ham operator..As it should be.

Hi Bill,

Thanks for the positive comment.

I just noticed that you and I share the same classic quote by the late (and great) Arthur C. Clarke in our postings. It is a wonderful quote as you no doubt will agree, one of my all-time favorites, and of course one of the three laws of Clarke. Actually, the quote you and I share is known as Clarke's Third Law.

I don't want to hijack this thread, so if you want, we can discuss Mr. Clarke off-line or start a new thread.

Best 73,

Bruce

[K5WLF]

When I start modulating the shack lights I know it's turned up too high.  Time to reduce power. 

You'd love a house I did some electrical work on out in Palm Springs (CA) years ago. Huge place, 9-hole golf course in the back yard, part of the swimming pool came into the house under a glass wall. A classic example of true conspicuous consumption.

The feature that'd make it ideal for QRO ham ops was the electrical service. Each half of the house was supplied by a 600A, 3-phase service. NEC at the time prohibited more than one service entrance for a single-family dwelling. But, I guess money talks and the NEC walks, at least in Palm Springs.

Sure would be difficult to modulate the lights though...

ldb

[Bill, KD0HG]

I just noticed that you and I share the same classic quote by the late (and great) Arthur C. Clarke in our postings. It is a wonderful quote as you no doubt will agree, one of my all-time favorites, and of course one of the three laws of Clarke. Actually, the quote you and I share is known as Clarke's Third Law.

I don't want to hijack this thread, so if you want, we can discuss Mr. Clarke off-line or start a new thread.

Best 73,

Bruce

I never noticed our duplication in tag lines before...I could switch to Law #1, which I like very well.

;-)

[W2XR]

I just noticed that you and I share the same classic quote by the late (and great) Arthur C. Clarke in our postings. It is a wonderful quote as you no doubt will agree, one of my all-time favorites, and of course one of the three laws of Clarke. Actually, the quote you and I share is known as Clarke's Third Law.

I don't want to hijack this thread, so if you want, we can discuss Mr. Clarke off-line or start a new thread.

Best 73,

Bruce

I never noticed our duplication in tag lines before...I could switch to Law #1, which I like very well.

;-)

Hi Bill,

I think Mr. Clarke would be highly flattered if he knew we were both quoting his Third Law.

Please do not feel obligated in any way to change your quote, just because I use it as well!

Then again, variety is the spice of life. If you do decide to quote his First Law, we will now need someone to include Clarke's Second Law as their quotation.

Does anyone here on the board want to adopt Mr. Clarke's Second Law for their quote? Here it is:

"Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible".

73,

Bruce

[kb3ouk]

The feature that'd make it ideal for QRO ham ops was the electrical service. Each half of the house was supplied by a 600A, 3-phase service.

What could they have possibly needed that much power for?
shelby

[K5WLF]

The feature that'd make it ideal for QRO ham ops was the electrical service. Each half of the house was supplied by a 600A, 3-phase service.

What could they have possibly needed that much power for?
shelby

I have no idea. The entire roof of the house was ringed with 150W PAR floods about 20' apart, entire 9-hole golf course was lighted, long driveway and all walkways looked like airport runways, HVAC, probably walk-in reefers and freezers, etc. We worked on the roof lights, added a few receps and put in some special track lighting for a new painting and that was all. Didn't go into but about four rooms of the house. Never met anybody except the butler and a couple maids. Never even saw the owners. Don't know what was in the parts of the house we didn't see.

[kb3ouk]

I just noticed that you and I share the same classic quote by the late (and great) Arthur C. Clarke in our postings. It is a wonderful quote as you no doubt will agree, one of my all-time favorites, and of course one of the three laws of Clarke. Actually, the quote you and I share is known as Clarke's Third Law.

I don't want to hijack this thread, so if you want, we can discuss Mr. Clarke off-line or start a new thread.

Best 73,

Bruce

I never noticed our duplication in tag lines before...I could switch to Law #1, which I like very well.

;-)

Hi Bill,

I think Mr. Clarke would be highly flattered if he knew we were both quoting his Third Law.

Please do not feel obligated in any way to change your quote, just because I use it as well!

Then again, variety is the spice of life. If you do decide to quote his First Law, we will now need someone to include Clarke's Second Law as their quotation.

Does anyone here on the board want to adopt Mr. Clarke's Second Law for their quote? Here it is:

"Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible".

73,

Bruce

I will. just changed it to clarke's second law.

[W3RSW]

"Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible".

I get all these quaint laws from the old optimistic era confused... 
e.g. Clarks with Asimov's three Robetic laws, Drake's equation, SETI hopes, etc. 

Once upon a time we were going to Mars by 1970.

I will say one thing for Clark though.... we now have 30,000 geo-synchronous competing, yammering satellites, not to mention zillions of LEO's.

We've killed space with multiple gnats whilst letting the really significant stuff rot in the archives.

Additionally, one of the oldest sci-fi themes around is the civilization that never makes it off it's planet, just rots away, ossifies from it's own dumbing down and stagnant welfare states. 

Pick up some  Colliers issues of the early 50's to see  what we might have done.