Legal Limit on 160?

[Opcom]

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.

What is ambiguous about this?

Depends on the definition of "normal".

[k4kyv]

If the rule is so clear and unambiguous, why do you hear hams on this and other forums, as well as over the air, ask questions because they don't exactly understand it? I never ever heard anyone ask another ham to explain DC plate volts X DC plate current.

[K1JJ]

I dunno - I think it's pretty straight forward. 1500w pep output for all modes. Since most rigs today (probably 99.99% of them) use 50 ohms as an output, use a standard 50 ohm PEAK reading wattmeter into a 50 ohm dummyload. That should be within 15% accuracy. Plenty close.  Most any ham can do that.


For more accuracy and more sophisticated hams, use a 50 ohm dummyload and measure across it with a scope and use the formula.

As long as the antenna is 2:1 or less swr, the 50 ohm wattmeter will read with "reasonable" ham accuracy. Even if not, the difference between a 1000w pep or 2000w pep signal is negligible.


The argument about using open wire connected to a balanced tank circuit is so rare and out of the mainstream, it akin to keeping rules out there for spark gap or SBE rigs...

That said, the real issue is not how accurately we anally measure 1500 watts pep. It's really about our intentions as shown by the size of the finals and infrastructure we run in reality.  For example for ssb, a pair of 3-500Z's says one thing. A pair of 3CX-3000A7's says another...  
  

T

[WV Hoopie]

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.

What is ambiguous about this?

An honest question, how affordable is test equipment that will measure ONE RF CYCLE for 1500 watts PEP?

Craig,

[W3SLK]

Craig said:

An honest question, how affordable is test equipment that will measure ONE RF CYCLE for 1500 watts PEP?

Now there is an astute question!  

[K1JJ]

A scope across a 50 ohm load will show instantaneous RF voltage peaks. Put in a 100% modulating sine tone. Since the peaks are all the same amplitude, pick one, use the formula and there ya go...

Quite affordable.

T

[W5COA]

(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.
------------------
OK, I have to get in here and ask.
- First of all, I wonder about capturing one RF cycle at 30,000,000 cps which is exactly at the peak of a complex modulating frequency of 300-3,000 cps.
- Second, the reference says take the average power of that cycle. I thought we were reading PEP, not average.
- Third, if I do have a scope that can capture the (voltage?) event specified, do I measure from top to bottom of the envelope? If so, is the average zero? Or, do I measure from the top to the middle and take the RMS value? Or, is there some other way?
- Fourth, is there really a wattmeter out there that will perform this measurement? What is its accuracy? Can someone give me a model number? Is it FCC certified to make this particular measurement? I have been using a Bird 4314 lately, and if you put it on peak reading, it takes a while for the needle to settle down. Even then, I have to kind of eyeball the average of the needle wiggle. I doubt that it is capturing one cycle in order to make its reading.

Last, at least for this post: Don, I have one of those Mirage meters, but have never tried to read peak power. If I can get my 80m antenna back up this weekend, I will tune to the lowest SWR spot and read average and then peak. I will then report back on my results.

Jim

[W5COA]

From the Bird website FAQ section (I don't know who asked  the question):

Question / Issue
 
I recently purchased a Bird 43P I was told I could not use this meter to read AM power...even though I have the peak kit in it. Is this true? Can you please elaborate?

Answer / Solution
 
The 43P was designed to measure Peak Envelope Power (PEP), so yes, it can measure AM power.  However, there a few caveats to this.

First of all, if you are using voice modulation, your reading will jump around a lot based on the variations of PEP seen by the instrument in this case.

Secondly, the 43P is calibrated at Bird using a signal having harmonics of no greater than -50dBc.  If your signal contains harmonics that are higher than -50dBc, the instrument will not read correctly.  The only good way to determine if the signal has some large harmonics would be to use a spectrum analyzer.  The important thing here is that the harmonics represent real power, and this must be accounted for in some way.  Either the harmonics are eliminated through the use of a filter, or the aggregate power including the harmonics should be measured.  While it s possible to measure power using a spectrum analyzer, the accuracy is usually not optimal (+/- 1dB or so), and it is not usually a straightfoward process to measure aggregate power.  If the desire is to make an accurate measurement, a broadband terminating power meter, especially one that measures heating power, is the best choice.  The next best choice would be a terminating square-law diode power meter, as detectors of this type behave much like terminating sensors.  Bird's 5011 sensor would be a good terminating sensor choice once equipped with the proper attenuator on the input.  Following these two types of sensors, next best would be a sqaure-law in-line power meter such as Bird's APM-16.  The main issue with this measurement would be that the directional coupler will not respond the same at the harmonic frequency as it does at the fundamental.

Thirdly, if you are using the 43P in CW mode (carrier wave mode), then the 43P would function just as a 43 and would not be able to read the AM power correctly at all.  The 43 will read quite erratically, based on the modulation depth and scale position.
 


 

[Steve - WB3HUZ]

(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.
------------------
OK, I have to get in here and ask.
- First of all, I wonder about capturing one RF cycle at 30,000,000 cps which is exactly at the peak of a complex modulating frequency of 300-3,000 cps.

What are you wondering about? If you have a scope with a bandwidth greater than 30 MHz, you can observe one cycle on the display.

- Second, the reference says take the average power of that cycle. I thought we were reading PEP, not average.

We are. By definition it is the average power of one cycle at the peak of the modulation envelope, thus peak envelope power.

- Third, if I do have a scope that can capture the (voltage?) event specified, do I measure from top to bottom of the envelope? If so, is the average zero? Or, do I measure from the top to the middle and take the RMS value? Or, is there some other way?

Remember, we're measuring average power, not voltage. Average power is E²_rms / R. R is 50 Ohms.

- Fourth, is there really a wattmeter out there that will perform this measurement? What is its accuracy? Can someone give me a model number? Is it FCC certified to make this particular measurement? I have been using a Bird 4314 lately, and if you put it on peak reading, it takes a while for the needle to settle down. Even then, I have to kind of eyeball the average of the needle wiggle. I doubt that it is capturing one cycle in order to make its reading.

Ask yourself this question. If you are using a 4314 and it never reads more than 1500 watts PEP, do you think you are in danger of getting nailed by the FCC?

Last, at least for this post: Don, I have one of those Mirage meters, but have never tried to read peak power. If I can get my 80m antenna back up this weekend, I will tune to the lowest SWR spot and read average and then peak. I will then report back on my results.

Jim

[k4kyv]

(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.
------------------

Are they talking about one rf cycle of carrier, one rf cycle of one frequency component of one of the sidebands with a complex modulating frequency, or what?  I was always told that an AM signal is NOT a single carrier frequency that varies up and down in amplitude according to the audio waveform of the modulation.  The carrier is a steady, unvarying sine wave of constant amplitude, and the apparent envelope waveform is the result of interactions between the carrier and the sidebands, which are bands of separate, discrete signals, independent from the carrier, that show up on a spectrum analyser as lying symmetrically on both sides of the carrier, each frequency component of which has a far lower amplitude than that of the carrier.

So are we now back to believing that the AM signal is a carrier that varies up and down in amplitude, in sync with the audio that modulates it?

I thought that heated controversy had been resolved long ago, back in the 1920's.

[Steve - WB3HUZ]

What controversy? Both or true and correct. They are just different ways of displaying the signal.

What you see on a scope is the time display of all the frequency components. You wouldn't see an envelope otherwise.

Another way to look at it is how much variation will there be when the period of the carrier is something like 0.1 uS and the period of the modulation is something like 0.3 mS?

[WV Hoopie]

A scope across a 50 ohm load will show instantaneous RF voltage peaks. Put in a 100% modulating sine tone. Since the peaks are all the same amplitude, pick one, use the formula and there ya go...

Quite affordable.

T

Not picking an argument, are all transmitters operating into a pure 50 ohm load, and I can't remember if I've ever transmitted a 100% modulated sine wave. As a matter of face, I just speak into the mic.

My view point; going to be hard to pick out that one rf cycle with a voice modulating the carrier. Or am I still missing something?

Craig,

[K1JJ]

I axe myself this question...

I tune up my pair of 3-500Z's linear amp into a 50 ohm dummy load. Using a standard Bird 43 PEAK reading wattmeter I use a dead carrier and adjust the output for 1500 watts. This is about all the amp will put out before saturation.

Now I try my Belcher, a 12% duty cycle pulse on ssb- still 1500 w peak. I try CW - still 1500w peak on the Bird. I try a Yallo on ssb - still 1500 w pep. I then whistle on AM - 1500w pep on the meter.  An atomic Yallo on AM - I still see 1500w peak on the Bird meter.

Bottom line is no matter how the amplifier is driven or modulated, I see 1500w pep (PEAK) on the Bird or using the scope/dummyload method.

Remember that an AVERAGE reading wattmeter will not show all this. It will show 180 watts with the belcher, 375 watts on AM, etc. A FAST integrating PEAK reading wattmeter is what's needed to see 1500w on all the previous examples..

Why make this difficult? One cycle or  1 million RF cycles using any audio waveform will produce about the same peak output as long as the amplifer is loaded up to its max, in this case, about 1500w out.

A class C plate modulated rig should perform similarly with audio if driven to near saturation.  If the peak reading meter says more than 1500 w, then the cookie company will come a-knocking....  Seriously, 1500w is just a rough guideline.  If invited, I could come to anyone's shack with my peak Bird and 50 ohm dummyload ( must have a 50 ohm rig) and tell you very easily your peak power output with good accuracy. Good enuff to satisfy any regulation. Simple..


T

[K5IIA]

 

[W5COA]

Back up to my post that copied the response from the Bird tech support guy. If I read him right, it is going to be difficult to accurately measure an AM voice modulated signal. He says that the reading with voice modulation jumps around, and harmonics degrade the measurement. He goes on to say that a heating element provides the best measurement, but it probably is not capturing one RF cycle.

In my posts, I am trying to understand how to make the measurement as specified by the FCC regulations. It does not appear to me that the Bird 43 series does that, no matter what the meter reads.

My experience with the 4314 is in measuring a non conventional/conventional two way radio system, and I don't have the instrument available to me to take home and hook up to my AM TX. Wish I did.

Jim

[WV Hoopie]

Mr Vu:

Ok,, with the scope/dummy load thing. Have to guess; you are measuring voltage developed across the dummy load? Do you use a probe to keep the voltage developed from zapping the scope? Then its E=IR, or I=E/R, then using I with measured voltage on the scope to get power? Watts=E x I.

If that is the method, not to difficult. But few hams have a scope, let alone a probe. Still the rf pick-up used for my scopes to watch a wave form pattern will not give me that needed info for every day use.

Tnx,
Craig

[K1JJ]

I've compared my Bird peak readings on AM using speech audio to the readings taken from a scope across a 50 ohm dummy load and find them reasonably close.  

If you suspect the Bird readings, then I would rely on the scope readings across 50 ohms. Not much better than that and no FCC inspector would find fault. AFAIK, don't they themselves use  Bird peak capable reading meters or the equivalent in the field for proof measurments?


T

[KG6UTS]

I liked the old DC/PA figure...it was figgerin' on the best shot up the pipe with all the umph you had. Nobody asked about erp etc....Geeze.....any figure you want to do into a bad feed/antenna might not even light a bulb. ~8^o...

EdZ KG6UTS....who still deals with bad feed and antennas

[K1JJ]

Mr Vu:

Ok,, with the scope/dummy load thing. Have to guess; you are measuring voltage developed across the dummy load? Do you use a probe to keep the voltage developed from zapping the scope? Then its E=IR, or I=E/R, then using I with measured voltage on the scope to get power? Watts=V x I.

If that is the method, not to difficult. But few hams have a scope, let alone a probe. Still the rf pick-up used for my scopes to watch a wave form pattern will not give me that needed info for every day use.

Tnx,
Craig

Hi Craig,

Sorry, I should have posted the power formula... duhh...

Use any standard 500 volt X10 scope probe and measure the peak to peak RF voltage across the 50 ohm dummy load. Say you read 275v p-p. Then square this and divide by the impedance, 50 ohms.  So, 275V (peak to peak) squared = 75,625 /50 = 1512.5 watts peak.


Try it and tell me how close it reads to your wattmeter when into a dummyload - I'd be curious. Use your voice.  You have a peak reading wattmeter to compare to?


T

[Steve - WB3HUZ]

More on using the scope at these two links.

http://www.ab4oj.com/test/peptest.html

http://www.ab4oj.com/test/pwrmeas.html

[k4kyv]

A clear demonstration that the FeeCee shot themselves in the food with that p.e.p. bullsh!t.  Even experienced knowledgeable hams either don't agree exactly on what the power limit is, or don't fully comprehend what the regulations say.  That being the case, what could one expect from Joe Bloe Hammy Hambone with the typical level of technical expertise we see from to-day's question-pool licensees?

The fact that we are still debating and discussing this issue two dozen posts later proves my point.

[WV Hoopie]

Steve & Tom,

Good info, I'll have to play with it and see what numbers turn up. Tom, I don't have a peak reading meter. Doubt the Junkston "500" exceeds the limit and if it does, it ain't by much. Now the Desk KW, well I only run it on low power . And that's bout 220 watts of carrier, not even close.

Have to agree with Don, it was so much easier to multiply the voltage times the current. If I remember the regs, those two meters were only required on transmitters which exceeded a certain power level. Was it 750 DC input?

Craig,

[Steve - WB3HUZ]

I think it was anything over 900 watts.

Yes, E x I is/was simpler. But PEP is the rule of the day. If we AMers want to claim we're technically proficient, we should understand PEP, even if we really never use it.   

[WD8BIL]

Whoops, never mind!

I think the regulation to use in these cases is:
"... enough power to maintain reliable communications!"

[WA1GFZ]

I requested the FCC provide a test method and a time constant on PEP when they came up with this crazy method. They never responded. In the Mil world a test method is provided.