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Author Topic: 1500 pep output max  (Read 94976 times)
K7KBN
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Posts: 3693




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« Reply #30 on: December 25, 2015, 11:30:56 AM »

"RMS power is an invention of the audiophools and now some technically challenged hams have picked up the new buzzword."

OK, I guess I was getting carried away with my terminology.  I was trying to get across that the PEP power we are discussing is based upon RMS voltage and RMS current.  I apologize for the confusion on that detail.

I'll say it definitively: The term RMS power is incorrect.  There is RMS voltage and RMS current but when we discuss power, it is simply power.  We can talk about peak power, average power, or even Peak Envelope Power.  Power is exactly true heating power when we are discussing RF power.

Gary - N0GW

As I was told by a Radio Shack clerk back around 1970 (shortly after the FTC laid down the requirements for how audio equipment power "shall" be rated):

"RMS?  That stands for 'Real Music Sound'"!
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73
Pat K7KBN
CWO4 USNR Ret.
AA6CJ
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Posts: 95




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« Reply #31 on: December 25, 2015, 01:16:04 PM »

I think we are at the gist of it now.  Had I been aware of the ITU language, I would have asked the question to say has anyone petitioned the fcc to make the power level based on mean power.  The question is to address that the average power is 20-30% under pep.  I apologize if I started us down the rabbit hole not being sure whether I should refer to it as average or rms power.  My bad. 


Going back to my question, I wonder if one could measure mean power properly for ssb?  And, .25s doesn't "feel" like a long enough interval.
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REASTON
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« Reply #32 on: December 25, 2015, 01:25:47 PM »

I think we are at the gist of it now.  Had I been aware of the ITU language, I would have asked the question to say has anyone petitioned the fcc to make the power level based on mean power.  The question is to address that the average power is 20-30% under pep.  I apologize if I started us down the rabbit hole not being sure whether I should refer to it as average or rms power.  My bad.  


Going back to my question, I wonder if one could measure mean  power properly for ssb?  And, .25s doesn't "feel" like a long enough interval.

Mean or average power in reference to SSB doesn't work as a good way to measure output power because it is dependent upon the characteristics of an individuals voice. Not easy to measure.  Peak power is not easy to measure with much accuracy either.  The FCC probably should have just left the old way of measuring power in place because it was simpler and only common cheap metering needed to be used to measure average input for SSB.  
« Last Edit: December 25, 2015, 01:39:31 PM by REASTON » Logged
AA6CJ
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Posts: 95




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« Reply #33 on: December 25, 2015, 01:43:26 PM »

thanks

I will work on the audio side to maximize my signal mean power without it sounding horrible.  Wouldn't know what could be said to fcc to replace that we have.  Great for cw and rtty though having 1500 pep.
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KM1H
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« Reply #34 on: December 25, 2015, 02:31:25 PM »

Quote
Up to two years ago, the Swedish Power limits were expressed as an undefined "maximum power" of 1000W.
There was no guidance in the rules how this was defined or should be measured, in contrast to other Administrations that used the ITU defintions.

Sounds smart to me, let a sleeping dog lie as the old saying goes which might go back to the Egyptians of old.

Carl
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G3RZP
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« Reply #35 on: December 25, 2015, 02:55:29 PM »

Quite how it got done but here we got the power limit of 400 watts PEP (or whatever - it's band dependent) at the antenna. As I understand it, that was because of the argument that at V/U HF, transmission line loss needed overcoming.

Now with an antenna feedpoint impedance on 160 of something like 1200 + j550, the chances of measuring power at the antenna to any degree of accuracy are pretty remote....

Fortunately, with budgetary constraints being what they are, unless there's a problem, the administrations don't bother too much these days unless there's a problem.
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W9IQ
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« Reply #36 on: December 29, 2015, 01:50:41 PM »

I think the FCC General Class question pool expresses the measurement technique quite simply:

Quote
What is the output PEP from a transmitter if an oscilloscope measures 200 volts peak-to-peak across a 50 ohm dummy load connected to the transmitter output?
B. 100 watts

Take note that this is using the maximum attained RMS voltage of the modulated carrier - which is essentially a sine wave.

In practice, a PEP meter is simple to fabricate. A peak envelope voltage detection circuit (< $2 USD) makes quick work of the measurement if one assumes a 50 ohm load. Take the peak envelope voltage value, square it, then multiply by 0.0025 and you have the PEP (peak envelope power). A $2 USD PIC processor can do the math and drive the display. No need to worry about time averaging or any of the hand wringing issues raised in this thread. And the best part is you don't have to try to interpret bouncing needles or rapidly changing digital displays.


- Glenn W9IQ
« Last Edit: December 29, 2015, 02:25:16 PM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KK4YDR
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Posts: 673




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« Reply #37 on: December 29, 2015, 05:38:49 PM »

It's all about ERP.

Bingo!!

Effective Radiated Power can make that 1500 watts seem like 5000 watts depending on how well designed, constructed, and efficient your antenna system is.

Using this calculator, assuming all background mathematics is correct, http://www.csgnetwork.com/antennaecalc.html

at 1500 watts with a 2.1dBd (As in dB(dipole)) in gain should net me around 4600 watts effective power. That is an amazing amount of focused power over a unity (0dBd) gain dipole antenna. So in essence a flat top conventional dipole antenna, having a unity gain, should have an ERP of 1:1 meaning 1000 watts in 1000 watts out. Of course this is not representative of feed line losses or other inefficiencies i.e. insertion losses from different toys that you put on your antenna system.

Since I actually only transmit at 100 watts through my ladder line fed antenna with absolutely minimal feedline loss (Cheer for 450 ohm woohoo) I should be putting out 270 watts ERP or roughly another S unit or so extra over barefoot 100w.

I like to measure my numbers for ERP via dBd because it gives me a real source of comparison and something tangible since no on really has a Isotropic point of reference as in dBi. But this is all just my opinion.

Lastly a Yagi for instance measured typically in dBi due to their usually being mounted way atop a tower, in this example lets say a 20 meter Yagi measured around 14dBi with 100 watts fed to it will have an ERP in excess of 2.5KW, That is why so many amateurs bite at the bit to get a tower and a Yagi airborne. They are that good :p

My point of reference is my 80meter horizontal loop about 65' off Earth at all points fed with 450 ohm window line.

« Last Edit: December 29, 2015, 05:43:32 PM by KK4YDR » Logged
NO2A
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Posts: 1400




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« Reply #38 on: December 29, 2015, 09:14:51 PM »

It's all about ERP.
Likewise, 1500 watts into a 160m hamstick (if it could handle it which it can't )would still be -0db gain.
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KM3F
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Posts: 910




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« Reply #39 on: December 29, 2015, 11:14:13 PM »

2500 watts peak at the output jack.
How much it takes to produce this has no bearing.
Envelope is the top of the output wave form no matter what the shape is below the peak.
How many rms, goats, pigs,  chickens etc watts below the peak makes no difference in reference to the  'rule'.
ERP is independent because it's what you do with the 1500 watts peaks after the output jack, at the ant and direction that makes up the ERP.
The effects of the  1500 watt limit can be enhanced under the peak power by increasing the average under the peak in an amplitude voice mode.
This can be done by using compression methods to raised the average under the peak, rule.
.
In CW, you have no opportunity to do this because the peak is always what is present with the carrier keyed  on.
The only difference is the repetition rate has an average power but it's effects are not the same as varying  voice averages.
The main effect of increased keying speed is to raise the power consumed by the amplifier the faster the repetition rate becomes making it look more like an AM modulation of the total power because it still has the same peak power as  AM drive signal has but has near straight sides to the signal instead of varying shape voice irregular  wave type of drive signal.
The effects of ERP are still available in all modes because it's still a function of what you do with the power 'after' it leaves the amplifier.
The PEP  rule is tough to get around but it does allow you to increase the average in a voice modes that would be harder to regulate and measure as a DC input unless instrumentation is used like we have for RF.
In AM mode, the carrier is the reference point. At 375 watts max carrier times 4 for 100 % modulation = 1500 watts.
You can still raised the average under the peak and get the same benefit result  for signal as SSB except for less efficient and wasted  side band power.
But  the rules don't address that.
Good luck.

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KM3F
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Posts: 910




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« Reply #40 on: December 29, 2015, 11:23:55 PM »

The  only instance I can come up with for ERP as the rule is the 5 channels on 60 meters.
That is done for a totally different purpose to limit QRM to other services in the same band as well as the frequency and bandwidth has to be precision to specified  limits.
Good luck.
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G3RZP
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« Reply #41 on: December 30, 2015, 02:46:04 AM »

About 20 years ago, in European standards and regulatory requirements, ERP was used below 1 GHz and EIRP above, on the basis that a horn antenna can have the gain over isotropic accurately determined by the physical dimensions and so measurement was likely to be more accurate. The difference between ERP and EIRP is defined as 2.16dB. Now recently the ITU seem to have been persuaded that for the new 472kHz and 5 MHz allocations, the power limit should be EIRP - possibly at the insistence of the Russians who were against those allocations anyway. Actually measuring radiated power with accuracy is not an easy task, anyway, especially if you don't have a calibrated antenna range and are working at HF - above 300 or so MHz, using a fully anechoic chamber makes life a bit easier.
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SM0AOM
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Posts: 261




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« Reply #42 on: December 30, 2015, 03:39:56 AM »

About 20 years ago, in European standards and regulatory requirements, ERP was used below 1 GHz and EIRP above, on the basis that a horn antenna can have the gain over isotropic accurately determined by the physical dimensions and so measurement was likely to be more accurate. The difference between ERP and EIRP is defined as 2.16dB. Now recently the ITU seem to have been persuaded that for the new 472kHz and 5 MHz allocations, the power limit should be EIRP - possibly at the insistence of the Russians who were against those allocations anyway. Actually measuring radiated power with accuracy is not an easy task, anyway, especially if you don't have a calibrated antenna range and are working at HF - above 300 or so MHz, using a fully anechoic chamber makes life a bit easier.

To accurately determine actual radiated power, antenna efficiency and ERP in the HF range it takes a helicopter with a field-strength meter with a data logger and some quite special software (and a large budget). Back in the days when there was a market for MF and HF broadcast antennas this was often done for contractual purposes.

The reasons for use of EIRP in the 5 MHz case is that most current HF circuit and interference prediction software use EIRP as one input parameter.
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W9IQ
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« Reply #43 on: December 30, 2015, 02:50:06 PM »

To the OP's question, PEP is the easiest to measure so I would not ask the FCC for any changes.

Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
AA6CJ
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« Reply #44 on: December 30, 2015, 03:03:24 PM »

That's the message that I copied.  Hi.
73 thanks for the interesting and educational discussion.
Fred, aa6cj
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