Define "Tall Ship"

[k4kyv]

If they ever do try to measure the power on an open wire line, I'd like to see a video of that.

http://www.youtube.com/watch?v=jocRd-aajW0

[W7TFO]

Use this formula and a meter like that:

RF Volts squared, divided by the line impedance.

73DG

[kb3ouk]

You could also place an RF ammeter on each side of the line, then use P=I²R to get the power. Having one on either side would be a good way to tell if there was any imbalance in the feed line. The FCC would accept that for sure, since that's how AM broadcast power is measured at the tower (of course, they're only dealing with a coax line, not open wire).

[K5IIA]

Watt meters are a major cause of distortion at many stations.

[steve_qix]

When I had an inspection (I passed with flying colors), The inspector told me they use HP or Bird meters and the hard and fast rule is 1500 pep no matter the mode. I agree with most that this is wrong for AM mode. 

Wow!  When and WHY did you get inspected?  That's really something.   Was there in interference complaint or something?

[k4kyv]

And I was wondering how they performed the inspection.  Did they just measure the carrier output with the transmitter running, or did they ask you to modulate?  And was that modulation with a tone generator, or just your voice?  Since all voices have different waveforms, an individual's voice test would be questionable. A few months ago someone on this board mentioned that their station had recently been inspected, and the inspector simply placed his Bird wattmeter in the coax line and had him turn on the carrier, and that carrier indicated less than 1500 watts, so the agent said he was OK.

About 20 years ago Roger, N4IBF(SK) was inspected due to the chronic complaints of a nearby nut-case who claimed Roger's signal was preventing him from hearing the baseball game on his portable AM radio.  Roger was running a BC-610 which had been modified with an SO-239 replacing the original output terminals.  The agent did connect his Bird wattmeter to measure his power as part of the inspection, but he kind of laughed about the whole thing,  leaving the impression that the guy was crazy and he was just doing his job, hoping to shut him up.

[Steve - K4HX]

Both the time domain and the frequency domain show "the physical reality" (whatever that is). They both show the same information. Any claims to the contrary are false. Any claims of anything other and PEP equaling 4x the carrier power at 100% modulation are false. This is getting silly.

[kb3ouk]

When I had an inspection (I passed with flying colors), The inspector told me they use HP or Bird meters and the hard and fast rule is 1500 pep no matter the mode. I agree with most that this is wrong for AM mode.  

He told me that if you have an RMS or AVG meter OR a scope,  Take the reading of the carrier and times by 2.828 to arrive at pep.  I knew this before he mentioned it and have used that for years. It works out perfectly every time.

Modulate the rig to 100%. take the carrier and times by 2.828 and get the pep.  Most commercial watt meters use this principal so they also read 2.828 times over.  Take your HP, Bird coax dynamics ect peak reading meter and try it.. When you hitt 100% mod, that meter will read 2.828 times higher period.  

So are you saying that the FCC (the ones who made up these rules) are lying? Ok, sure the absolute peak power may be 4x the carrier, but read closely what Don posted:

The fee-cee's definition of p.e.p., the average power of a single rf cycle at the crest of a modulation peak

Or, how the FCC words it under Part 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.

So here I am modulating my transmitter. Let's make things simple. the final is running 2000 volts at 250ma and is 75% efficient. That gives me 375 watts of carrier at 500 watts input. When my voice causes the transmitter to become 100% modulated, the peak input is will be 2000 watts, which means the peak out is in fact 1500 watts. But, according to their own rules, they are only concerned with the average of the peak. Well, let's jump back to what the inspector told Clark: "2.828x carrier is peak." Where did they get the 2.828? Time for another quote from Don:

To digress for a moment since you brought up the subject of specific power meters, one of the reasons the fee cee decided on the p.e.p. standard (aside from John Johnston's longstanding anti-AM bias) for the output power rule instead of a more appropriate average (aka mean) power standard, is that there were no true average-reading wattmeters available on the consumer market.  A so-called average reading wattmeter such as the Bird 43 is in reality an average-reading rf voltmeter, with scale calibrated to indicate watts into a specifically defined resistive load.  The problem is that average power is NOT equal to average voltage X average current, but rms voltage X rms  current.   BTW, there is no such thing as "rms power" or "rms watts". Likewise, average voltage X average current of a complex waveform is a meaningless calculation.  Instruments like the Bird 43 are capable of reading average power only in the case of a steady unmodulated carrier or a non-amplitude modulated carrier such as an FM or FSK signal.  There were no average reading watt meters readily available at the time; the closest we could come at a  reasonable cost was the thermocouple rf ammeter, calculating average power derived from rms current using Ohm's law, just like the Bird 43 calculates power derived from RF voltage via Ohm's law. The main problem with the rf ammeter is that the movement is too sluggish to indicate the average power of a signal with high peak-to-average ratio like slopbucket.  That has changed; Bird now offers the APM-16, an accurate, true average-reading wattmeter, derived from its active-circuit capability to accurately measure the RMS voltage of a complex waveform.

That 375 watts of carrier is the RMS value, not the true average. Take 375 times the square root of two, and that gives you the average power, which is about 530 watts. Now take that value times 2.828 and you get about 1500. The FCC got that 2.828 value by dividing 1500, which would be the peak output of the transmitter based on (Ip x2)(Ep x2) / (efficiency), by the average of the carrier, which for a transmitter running at 375 watts RMS volts times RMS amps, would be 530 watts average.

[N8AFT]

  I found the video to be quite instructive...

[W3RSW]

All this is moot, just hardware.
People are running 3cx3000's routinely, not to mention .. cx10 k's.
Our real problem is content, "software," being able to even have ham radio stations.
The real fear is that the FCC may kick us off the air entirely.  We'll all be pirates regardless of PEP.  It's apparently easy for the fed to shut down the Internet, ham radio, whatever.
Only the law abiding are affected, of course. Oh, and then we could be shut down by mode, starting with AM.  Easily Monitored digital modes the last to go or to stay very restricted.
We'll be in a real ghetto, that is only allowed to operate from sanctioned hobby clubs.

And speaking of PEP, ave power, etc. it's instructive to look at all the signals on a SDR. Hard to prove who's loud because of power and who's loud from propagation. Over time with signal analysis, location ID, etc., very easily obtained by, say, comparing CW Skimmer calls, a case can be built that John Ham deserves an inspection visit. Most "visits" of course are from complaints, human nature being what it is. 

As to mathematical vs, real waveform constructs, several of us could post or refer to the literature AM analysis. I most usually fall back, from a good mix of practical and math standpoints, on "Electronic Designers Handbook" Landee, Davis, and Albrecht, McGraw Hill.
Modulation is described as a series expansion of the superposition of two signals, and onward to the integration of side ands, etc.  Both time and frequency domain are illustrated as well as a nice vector representation. Suffice to say, "amplitude modulation of a carrier increases the total signal (carrier plus sidebands) power by the amount of power present in the sidebands signals."

[Bill, KD0HG]

Long time ago, I had a chat with one of the people in Johnston's Washington office.

He told me that one of the reasons for the change to the PEP standard (from 1 KW DC input) was that "..We aren't going to put our inspectors in danger by having them measure high voltages inside a transmitter...".

Bill

[W3RSW]

You will find that labor law, regardless of whether from a zero lift facility including nursing homes all the way to dear FCC techs, is safety biased in favor of the "laborer" not the customer or the proprieter.  There are good reasons but should be clearly thought through.

Safety issues are the most easily leveraged in any negotiations and always have unintended consequences.

[Bill, KD0HG]

Yes, Rick, but I have seen some old buzzard transmitters that I wouldn't ever want to stick my fingers into!

FCC inspectors have never had to go inside of AM broadcast transmitters to measure DC input power, they measure the antenna system impedance with a bridge and then the RF current into the antenna to calculate carrier watts.

They simply instituted a similar system for hams.


Bill

[ke7trp]

I am speaking of the how the instrument will read steve.

The instruments they use to measure pep power operate on a 2.828 times RMS to arrive at pep.  If you tune your rig for 4 x on such meters, you will be way off carrier to 100% mod period. 

I am not talking about any RF theory of how the carrier and side bands operate. I will leave that to the experts here..  If you own a pep meter and use it to tune your rig and go 4 x like people tell you, You are likely overmoding and splattering all over the band.

Please dont take my word for it I am simply paroting what the inspector told me. Try it yourself.  Simply calibrate your scope on a carrier, Increase modulation until the scope is just touching 100 % mod.   Read carrier and pep on the meter the FCC uses and carried INTO my home.  The reading will be exactly 2.828 times just as the inspector told me it was.

I have tried this on every transmitter I have and every single time. It shows a bit less then 3 times right at 100%. That is unless said transmitter cant reach the 3 times mark



C

[Opcom]

Simply calibrate your scope on a carrier, Increase modulation until the scope is just touching 100 % mod.   Read carrier and pep on the meter the FCC uses and carried INTO my home.  The reading will be exactly 2.828 times just as the inspector told me it was.

C

What waveform is to be used for modulation in this test or does it really matter?

[Steve - K4HX]

I've never seem any such thing. Why would you use RMS and how would you measure that on a scope (without doing some math)? If the FCC told you this, they are completely wrong.

It's simple. When you measure 100 percent on the scope, you are measuring a 2x voltage level compared to the unmodulated carrier. 2x the voltage is 4x the power. If your meter read differently, it's incorrect. Anything else is pure nonsense.

I am speaking of the how the instrument will read steve.

The instruments they use to measure pep power operate on a 2.828 times RMS to arrive at pep.  If you tune your rig for 4 x on such meters, you will be way off carrier to 100% mod period. 

I am not talking about any RF theory of how the carrier and side bands operate. I will leave that to the experts here..  If you own a pep meter and use it to tune your rig and go 4 x like people tell you, You are likely overmoding and splattering all over the band.

Please dont take my word for it I am simply paroting what the inspector told me. Try it yourself.  Simply calibrate your scope on a carrier, Increase modulation until the scope is just touching 100 % mod.   Read carrier and pep on the meter the FCC uses and carried INTO my home.  The reading will be exactly 2.828 times just as the inspector told me it was.

I have tried this on every transmitter I have and every single time. It shows a bit less then 3 times right at 100%. That is unless said transmitter cant reach the 3 times mark



C

[k4kyv]

Both the time domain and the frequency domain show "the physical reality" (whatever that is). They both show the same information. Any claims to the contrary are false. Any claims of anything other and PEP equaling 4x the carrier power at 100% modulation are false.

The issue is not whether or not the power peaks at 4 X the carrier power, but the erroneous definition in Part 97: "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."

One rf cycle of what?  The carrier? The most prominent audio component of the modulating signal?  As it was demonstrated sometime circa WWI, there is no single frequency in an amplitude modulated signal in which the amplitude of "one rf cycle" can be observed.  It's a conglomeration of numerous rf cycles including the carrier wave and all the resolvable components of the sideband spectrum lying on each side of the carrier.  Try to monitor the envelope pattern of an AM signal with a scope, and then increase the sweep frequency until the rf sine wave of the unmodulated carrier is clearly displayed.  Once the trigger circuit locks the sweep oscillator to the carrier, the screen displays a perfect sine wave, but when modulation is applied, you don't see that sine wave varying up and down in amplitude in step with the modulating frequency; in fact you no longer see a perfect sine wave at all. The entire trace becomes fuzzy and poorly defined. This is observed on a bench scope good up to somewhere beyond 250 mHz even when monitoring the output of a 160m transmitter.

If their intent was the 4X standard, it should read something like "the total mean power delivered to the antenna during the crest of the modulation envelope".

Long time ago, I had a chat with one of the people in Johnston's Washington office.

He told me that one of the reasons for the change to the PEP standard (from 1 KW DC input) was that "..We aren't going to put our inspectors in danger by having them measure high voltages inside a transmitter..."  FCC inspectors have never had to go inside of AM broadcast transmitters to measure DC input power, they measure the antenna system impedance with a bridge and then the RF current into the antenna to calculate carrier watts.

They simply instituted a similar system for hams.

No, they instituted a far different system for hams. The AM broadcast service goes by the real, effective power the transmitter puts out, i.e. the number of calories the rf energy would generate to measurably raise the temperature of a dummy load when the output of the transmitter is delivered to that load.  By "Fee Cee Magic", a 375 watt amplitude modulated carrier in the amateur service is supposed to be equal to approximately 750 real heat-producing watts of slopbucket. (Johnston once said this was "levelling the playing field".)  As noted previously, Canadians are smarter than United States-ese; their regulatory agency found it very simple and no problem at all to word the text of the Canadian power limit without according preferential treatment or discrimination to any mode:

Standards for the Operation of Radio Stations in the Amateur Radio Service                             RIC-2

(a)  where expressed as direct-current input power, 1,000 W to the anode or collector circuit of the
    transmitter stage that supplies radio frequency energy to the antenna; or

(b) where expressed as radio frequency output power measured across an impedance-matched load,

    (i) 2,250 W peak envelope power for transmitters that produce any type of single sideband
        emission, or

    (ii) 750 W carrier power for transmitters that produce any other type of emission.

[Steve - K4HX]

Completely incorrect. You can easily observe one RF cycle with the proper oscilloscope. Such scopes did not exist in WW1 but they have since at least the 1960's. The variation in the amplitude across the envelope is easily seen using the time base delay. Get a better scope or learn how to use the one you have. Sheesh.

[W2VW]

I am not talking about any RF theory

Quite accurate.

[Opcom]

There is very little excuse to blame measurement hardships on the scope.

A good scope with a high intensity tube, like a Tek 7904, can allow the viewing of the very few tallest RF cycles by using the trigger level carefully.

A digital scope makes this easier but is not required.

A crappy scope will also do, even if it won't trigger properly by RF. It can be reasonably assumed that the tallest RF cycles occur always during the "crest", so in this case the room can be darkened and the scope free run to see the extent of the vertical deflection. It is enough to say that is a measurement very close to "one RF cycle at the crest of the modulation envelope taken under normal operating conditions." It is true because the only cycles of interest are the tallest ones and this crest is visible because it is not covered up by the lower amplitude ones.

If the scope is really, really crappy, drive the TX with a trapezoid or slightly clipped sine wave to give the RF more time at its crest, and increase the intensity there.

Therefore it is only necessary to calibrate the scope a simple way. most people who have a scope set the TX to 375W with a good meter, observe this on the scope, and then call it 1500W when the trace is grown to twice the height.

Please lets not get into differences between a test using a tone and voice use. I believe "normal operating conditions" refer to the setup and tuning of the transmitter as it is regularly used, more than to whether a sine or voice is applied to the modulator for a test.

What is more important is the accuracy with which the FCC can measure the actual power, aside from reactive loads and impedances not 50 Ohms. Nothing matters except that the FCC inspector is satisfied as to where 1500W is according to his instruments in the context of the amateur's system. How accurate is a Bird 43? Can the scale even be read to that accuracy? Is the FCC going to ding someone for being off by 10% when the very act of field measurement itself is full of compounded errors due to instrument tolerances? Will the discrepancy ever matter at the listener's end?

If the meter is inserted onto the RG-8 line between the TX and the tuner, even though all is perfectly matched, and the true impedance is not really 50 Ohms, the 'bird watts' reading can be off. It won't matter for TX performance with a quite short piece of cable on HF. It's no secret that transmitters with roller inductors as well as variable tuning and loading caps can match all sorts of loads that are not 50 Ohms. Tuners can also accept a rather wide range of input impedance, not just output. It is easy to set the impedance of the coaxial link between the TX and tuner to any Z that works best.

This is mostly nit picking over the last 5% of instrument accuracy. Is the mast of my ship 10% shorter or taller than that of the one across town? I think more matters as to how it's made and how it's sailed, as to whether it is seen as a 'tall ship'.

[K5UJ]

Yes, I'd focus on the FCC power limit law double talk:

...erroneous definition in Part 97: "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."

After reading that I'd expect them to therefore show up with all sorts of exotic measuring equipment at a ham's station, but evidently, they show up with a Bird wattmeter, which isn't all that surprising because if you think about the rule and the measurement gear, it seems all rigged for basic continuous wave modes, AM being the only complex emission I can think of off hand (maybe spread spectrum is another one; not sure).

While no one has brought it up, I'd be cautious about challenging FCC on this--their solution to a serious petition might be to not change the rule or the way they measure power for AM on inspections, but to ban AM.    In some cases regulatory bodies see the "solution" as the easiest thing to do--make the problem go away.

 

[kb3ouk]

While no one has brought it up, I'd be cautious about challenging FCC on this--their solution to a serious petition might be to not change the rule or the way they measure power for AM on inspections, but to ban AM.    In some cases regulatory bodies see the "solution" as the easiest thing to do--make the problem go away.

A better petition might be just to ask them to put a footnote or something in the rules under power limits explaining the carrier to peak ratio for AM. But as to petitioning them to allow something, didn't the ARRL just petition them to allow single-slot TDMA and they allowed it? The whole reason behind that was that these guys were running TDMA repeater systems that they assumed were allowed under the way the rules were written, but the ARRL determined the rules were a little fuzzy, so petitioned the FCC to allow TDMA.  All we have to do is petition to clearly define the way PEP is determined and measured for AM. A less riskier move might be just to contact one of their engineers (if such a thing still exists within the FCC) and ask them personally.

[Tom WA3KLR]

I don't think that anyone here would pass a job interview given by Steve.

Patrick,

I don't agree with your Bird Watts column.  The Bird 43 works by looking at the line current in the center conductor and assumes 50 Ohms load.  The Bird Watts for your 10 Ohms situation would be 7500 Watts and for the 140 Ohms load it would be 536 Watts, and so on through that table column.

[W7TFO]

Math disCUSSions notwithstanding;

I'd like to know just what circumstances have brought an RI into a shack?

Real visits, not hypothetical if-thens.

In 40+ years of beating on broadcast gear I have been blessed with only two visits, and one was by invitation to resolve an interference complaint against the station.

73DG

[k4kyv]

I don't agree with your Bird Watts column.  The Bird 43 works by looking at the line current in the center conductor and assumes 50 Ohms load.  The Bird Watts for your 10 Ohms situation would be 7500 Watts and for the 140 Ohms load it would be 536 Watts, and so on through that table column.

Most "wattmeters" look at the RF line voltage and assume 50 ohms load.  I'm almost sure the Bird 43 works the same way, but I could be wrong; I have used them on occasions but don't own one.

I'd like to know just what circumstances have brought an RI into a shack?

Real visits, not hypothetical if-thens.

In 40+ years of beating on broadcast gear I have been blessed with only two visits, and one was by invitation to resolve an interference complaint against the station.

73DG

What about the other one?

If the meter is inserted onto the RG-8 line between the TX and the tuner, even though all is perfectly matched, and the true impedance is not really 50 Ohms, the 'bird watts' reading can be off. It won't matter for TX performance with a quite short piece of cable on HF. It's no secret that transmitters with roller inductors as well as variable tuning and loading caps can match all sorts of loads that are not 50 Ohms. Tuners can also accept a rather wide range of input impedance, not
just output. It is easy to set the impedance of the coaxial link between the TX and tuner to any Z that works best.

I have noticed in these discussions here and elsewhere it is nearly always assumed that every transmitter has a 50-ohm  coaxial output and that something like RG-8 is used to transfer power from the TX to the tuner, which then couples to the OWL, vertical, longwire or whatever.  But it is not carved in stone that every amateur station has to have a 50-ohm link anywhere between the final amplifying device in the transmitter and the radiating element in the antenna.  Maybe this is true with modern day plastic radios, but a few hams do still roll their own homebrew from scratch,  and may not opt to go the 50-ohm coax route.  Also, many of the popular WWII vintage military surplus rigs were never equipped with 50-ohm outputs.  The command transmitters are a perfect example of this, and so is the ART-13 and unmodified BC-610.  Look through the old 1930s Radio handbooks.  They even show antenna systems fed directly from taps right on the antenna tank coil, with no coupling link at all.  Probably one of the most efficient configurations of all (and less harmonic-prone than tapping onto the tank coil) is to use a push-pull amplifier with a balanced pi-network with a split-stator loading capacitor that works directly into balanced feeders with no link coupling coil or tuner at all (a configuration also described in the pre WWII Radio Handbooks).

The 1983 decision was  not the first time the FCC had proposed replacing input power with output power.  A few years earlier, ARRL had come out flatly against a similar proposal, with words in their formal  comments to the effect that "measuring output power in amateur stations was so unrealistic" that the  League could not support it.  The only change by the 1983 proceeding was the widespread availability of cheap  ready-made Hammy Hambone 50-ohm wattmeters on the commercial market, and the ubiquitous 50-ohm transceiver that had flooded the market in the intervening years. Little or nothing had changed in the actual technology. Even to-day, about the only real advancement in the relevant technology is the advent of the true average-power reading instrument like the Bird APM-16 or its equivalent.

I recall Bill Cross at one of the Dayton FCC forums made a remark about the new power rules.  He said if he had been the one who wrote the rules the way he would have wanted, he would have added the phrase at the end of the text on power standards "...as indicated on a Bird 43 wattmeter".