The AM Forum

What is the legal limit on AM phone?  First of all I just want say that I run 375 watts of carrier because that gives my amp plenty of head room with about 1200 pep on voice peaks.It will do about 1400 watts on slopbucket. I do understand the technical aspect of the 375 watt carrier.Iam more interested in the legal side of the question.    I have heard some of the guys say they were running 400 watts of carrier,and one guy claimed he was running 500 watts of carrier.Now is this still legal? ,if his pep doesnt exceed 1500 watts.And what about the guy running 4-3-500zs in grounded mode driving it with a MP 1000 Yeasu rice box claiming a 1000 watt carrier .Is that legal?Keeping in mind again his pep is presumably 1500 or under.I am realy interested in hearing you guys thoughts on this subject.

Very simple.....

1500 watts PEP.....Maximum

Operate with all the carrier you want....

Adjust the modulation to stay under the 1.5kw limit....

Fifteen thousand watts 8)

1500 watts of PEP in each 10 KHz wide sideband.  :D

I think your confused . I thought 15000 watts was the legal limit on the 11 meter band

Pppppfffft!  I swapped a 50KW Bird slug with a CB'er  for a piece of test gear.  :o

how about a pair of 3CX20,000A7,S  in a chevy suburban with 1 7/8 inch heliax as the feedline seen it!!!!

I'm guessing that was't running off the standard alternator. (Not even the heaters!)

That kind of wattage won't even get you heard on the Bowl lol.  As Stated further down the thread 2 3cx20,000 Com on. :o

But on a serious note, I run my Henry 2K classic at 400 watts of carrier and let it swing up too 1450 watts of pep.

Richard N6WDR

A limit 1500 watts of PA filament power works for me--of course this gives the Mosfet burners a real advantage.

1000 watts carrier
375 watts lower sideband
375 watts upper sideband

works for me until the slopbuckets from the land of the dumb come on top of me. Then it is your BTW spec.

(http://skullcracka.com/Photos/Jackson_2006/S4022155.JPG)

Multi alternators....

dayham...

Thats one massive serpantine, and there's idlers after every alternator?? Thats still for 12 volts?? And what, EIGHT HUNDRED amps???

-Jason kf6pqt

But they deleted the requirement to have "accurate means of measurement" of output power.  The R&O states something to the effect that amateurs are endowed with "means other than accurate measurement" to determine their power level.  ???  ???

There is absolutely nothing in the rules that mentions anything about a 375-watt carrier level.

All that expense and trouble - just to sound like you're talking through a kazoo. It don't make sense.  But that's just me.

http://youtube.com/watch?v=RMgj4Kdv71Y&mode=related&search=

"70,000 watts":
http://youtube.com/watch?v=E_41bynwlsU&mode=related&search=

you gotta swing that munky.....

You want to back it down if your plates start turning yellow......
Dull red is a safer legal limit for long life and avoids grid sag.
11N90 class E guys I find when your saturation voltage goes over about 1.2 volts the efficiency is heading south.

This is an interesting question that I have talked about for some time.  First of all, I am going to state that power cannot be "created".  It has to come from somewhere.  Consider the following scenario:

I have a theoritical transmitter whose RF amplifier operates at 1000 volts DC at 1 ampere for 1kw DC input at carrier.

Furthermore, I state that this transmitter has an efficiency of 75% (.75)  The RF amplifier is a square law device, and therefore can act as a mixer.  A modulated RF amplifier is nothing more than a mixer - producing 3 frequencies when modulated - the carrier frequency, the upper sideband (carrier + audio), and the lower sideband (carrier - audio).  The unmodulated RMS power output from this RF amplifier is 750 watts (.75 times 1000 watts input).

We also know half of the RMS power (RMS is the key word here - we also must get to the peak power) of the signal is contained in the 2 sidebands - 1/4 of the RMS power in each sideband.  This is substantiated by observing an AM signal on a spectrum analyizer.  The carrier DOES NOT VARY under amplitude modulation.  The sideband power varies with modulation and the carrier does not.

To get to 100% modulation, I'll need to supply a *peak* audio voltage equal to the RF amplifier's DC voltage of 1000 volts.  So now, I have 1000 volts peak across 1000 ohms which is a peak audio power of 1000 watts (p = v**2 / r)    p = 1000 squared / 1000 = 1000.  1000 watts?  1000 watts PEAK which is equal to 500 watts RMS.  RMS voltage = .7071 times the peak.  (.7071 times 1000)squared / 1000 = 499.99041 watts of RMS *power*.  So, everything works out.

The RF amplifier's DC input is 1000 watts carrier.  The audio adds another 1000 watts PEAK (500 watts RMS power from above), so we are, at 100% modulation,  putting 2000 watts PEAK power input into our system.  The RF amplifier's efficiency is 75% - its RMS carrier power is .75 times the DC input - therefore, the peak RMS power output from this system AT 100 % modulation is 1500 watts (PEP).

No power was created or lost in this analysis.

An AM signal is a complex signal consistaing of 3 distinct components (carrier, lower sideband and upper sideband).  It is not one signal "moving up and down".  Proper external measurement of an AM signal's power requires instruments that understand this relationship, or at least a proper use of instruments that don't.

Comments?

Regards,

Steve

I agree with ur analysis Steve.

It's my experience the cloud over the debate lies in the FCC's meaning of PEP.

"Sec. 97.313  Transmitter power standards.

    (a) An amateur station must use the minimum transmitter power
necessary to carry out the desired communications.
    (b) No station may transmit with a transmitter power exceeding 1.5
kW PEP."

Sec. 97.3  Definitions.
(b) The definitions of technical smybols used in this part are:

"(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... wouldn't that mean at the crest of the complex waveform envelope as seen on a scope ? (unlike that seen on a spectrum analyzer?)

I don't have an antenna transmission line.  My class e rig's output inductor is link coupled directly into the antenna loading inductor on my shorty dipole.

I wish the FCC would specify the power out as a maximum field strength at some specified distance from the antenna.  That way we wouldn't need to worry about directional antennas for transmission.

The 1KW DC input limit was nice in that the power level was easy to measure... klc

An interesting subject.  Some things to ponder:

1. In Steve's (QIX) math, and indeed most of us would use these formulas, these are RMS values and not average power.  Average power is not equal to RMS power when we're talking about complex waveforms.  The actual formulas are rather complex and involve integral calculus.  But from an older Handbook, it lists average voltage = .899 x V rms.  So that math comes out a little more in our favor.  But I am not a math wiz...

2.  The FCC in their infinite wisdom  ::) poorly defined their PEP formula.  The average power supplied....at the crest of the wave is not average at all as it takes one point in time! Not to mention that the definition implies a sinosoidal waveform.  Maybe the FCC should define how to accurately measure PEP power into a reactive load with a complex waveform?

So run whatever power you want, just don't bug your neighbor (unless he is on slopbucket    ;D

Pete
n1ps

Since I have absolutely no way of measuring output power, I use the "indirect" method I described above.  The indirect method, where one knows the efficiency of the transmitter, and the power input, is legal at Broadcast Stations is there is no current means of measuring the output power.   This will happen if the antenna array is way out of tune, or if the common point RF ammeter is defective.

My belief is that the FCC also accepts the indirect method, since the Amateur in question has made a good faith effort to accurately measure the station's power.  And, that measurement will probably be within 5% (or maybe better) of the output power... and that's pretty good !!!  Probably better, in fact that using an in-line wattmeter which may or may not be accurate.

My modulation monitor tells me whether the modulation is within legal limits, and I know the power output via the indirect method, so I feel pretty well covered at this point  8)

Very interesting discussion !!!

Regards,

Steve

I also use the 'indirect method'.  I have a thermocouple on my antenna tuner.

No wonder CBers are missing a few scroopples. All of that RF nearby can cause some serious cookin' in the ole body. I know that you can almost hug an antenna with legal limit at 160M, but 10KW of 11 meters within a few feet of one's head???????
This is the radiation formulas we did for our stations to make sure we weren't poisoning our neighbors and ourselves with RF.
Fred

 Interesting discussion .Ok I ran my carrier up to 400 watts the other night in the ghetto.Everyone said it sounded good.My 813s still arent showing any color even after a good old buzzard transmission.The pep is still the same ,the neighbors dont complain so I guess its ok.I realize that no one will notice a 25 watt power  increase at that power level ,but it does make me feel like I am more strapping now.Thanks.

QRO is a state of mind.

How may 813s do you have in your final, and in what mode are you running them?  In class C, a single 813 is good for 2000 volts @ 200 mA, no problem.

I can't speak to linear service directly, only to the calculations for figuring power v/s dissipation.

CRANK UP THE WICK !  You have  plenty more to go  8)

Regards,

Steve

 Hi Steve .My 813s are in grounded grid service,there are 2 in the amp now but I do have a third socket in there .I may add another tube later.Iwill have to add a couple more turns to the tank coil and then retap everything again on the band switch when I do.The  fillament are 10 volts at about 30 amps(overkill)so eventualy I could add 2 more tubes.I have 3 choices on my plate voltage 1400, 1800and 2200 vdc with 40 watts of drive at 1800 vdc I get 400 watts of carrier.My plate supply is capable of delivering that 2200vdc at about 1 amp{yep thats overkill again but I like overkill)and I had these parts on hand.A single 813 in groundid will take 120 watts drive before it starts to saturate,so you can double that drive for 2 tubes.813s are highly under rated tubes.My little plate modulated transmitter{a single 6146 modulated by a single 6L6 in a single ended ended modulator that uses a Johnson Messenger mod iron)only does 7 watts so I use a small grounded grid  amp to get that up to 40 watts.There are 3- 6LF6s (sweep tubes).Only run 400 volts on the plates and plenty of bias on the controle grid to keep em cool  durring an old buzzard and I like too old buzzard.This is  an ever evolving station so things tend to change as time goes by ,hopefully for the better.I am working on a bullit proof driver to replace the sweep tubes a single 813 that will give me 50 watts of drive in the middle stage and probably 500 watts overall  I have more ideas but thats another old buzzard transmission,73s.   

As you add 813s your tank coil needs to get smaller due to lower plate Z. Put all the voltage you can on the tubes they will love it in linear service. Add cathode bias if the resting current gets too high.
3 Kv will make them honk out real strappage in linear service.

A Friend of mine Ran a high powered mobile for CB (6000watts) in a 72 Chevy. He burnt all the rubber weather stripping of the doors and trunk. There digging tumors out of him now. These guys don't do this for fun they do it for money. They have a shoot out and bet big bucks to see who covers up whom.


73 de Gary KF9CM

I believe they call it a "key down" or "key down party" or somthing like that. I have heard some wild stories of guys that had to run nitrous oxide on the vehicle engines in order to make enough horsepower to run all of the alternators!! big egos, big money, and big bragging rights!  That kind of power at 27Mhz, in the hands of guys that dont know anything about RF safety!! Geeezzzeee, its definately kinda scarey!!

I BE WAVIN MY HAND IN THE BREEZE!! ABD I JUST GOT DOWN!! 8) 8)


                                               The Slab Bacon

If you can hear me I'm a runnin' legal limit regardles of what the wattmeter says !!!

Frank down here the call em shootouts.They used to have one in Raleigh and you could  here them guys here in Winston-Salem.     AND IM BACK QUIET READING THE MAIL CUMONE