Whats the legal limit on AM ?

[kf4qkr]

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.

[KF1Z]

Very simple.....

1500 watts PEP.....Maximum

Operate with all the carrier you want....

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

[k3zrf]

Fifteen thousand watts

[W1GFH]

1500 watts of PEP in each 10 KHz wide sideband. 

[kf4qkr]

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

[Ed-VA3ES]

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. 

[drradio]

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

[Ian VK3KRI]

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!)

[N6WDR]

Fifteen thousand watts

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.

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

[k7yoo]

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

[WA1GFZ]

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.

[Ed KB1HVS]

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!)

Multi alternators....

[kf6pqt]

dayham...

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

-Jason kf6pqt

[k4kyv]

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.

[W1GFH]

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

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=

[N3DRB The Derb]

you gotta swing that munky.....

[WA1GFZ]

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.

[steve_qix]

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

[WD8BIL]

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?)

[AB1GX]

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.

[KB2WIG]

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

[n1ps]

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   

Pete
n1ps

[steve_qix]

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 

Very interesting discussion !!!

Regards,

Steve

[AB1GX]

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

[flintstone mop]

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