AM power

Discussion in 'Amplitude Modulation' started by N2RDQ, May 15, 2018.

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  1. K4KYV

    K4KYV Subscriber QRZ Page

    Maybe not to that extreme, but I have heard crappy sounding undermodulated AM signals over the air, the operator explaininng that he was deliberately running his audio low to keep the pee-e-pee down.
     
  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    The pdf also contains this statement:

    "So the description, formalization, and use of PEP must have come about after about 1968, when advanced radar and digital
    techniques were on the horizon"

    This is completely wrong, and some archive research provides that it was first formalised in the mid-1940's.

    The earliest use of the PEP definition I have found is in Dutch and German literature from the early and mid 1940's ("Hüllkurvenspitzenleistung"). The concept and definition were literally used in one of the power definitions in the 1947 ITU Radio Regulations, and a discussion of the subject is reported in the Conference Minutes at page 548 of http://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.62.51.en.107.pdf

    For characterising the power and voltage handling properties of transmitter circuits,very good examples are the HF antenna couplers in high-performance aircraft, the application and understanding of the PEP concept and the related PEV (Peak Envelope Voltage) becomes critically necessary.

    In my first edition of Single Sideband Principles and Circuits from 1964, both concepts are used and discussed, as well as in early Collins marketing material and in AEEC and ARINC reports and papers from the early 50's.

    It seems that the current use of PEP for amateur power limits comes out of a general wish of the Authorities for handling roughly similar radio services in an uniform manner. Most other services, except AM sound broadcasting which is on its way out, have their power levels characterised and regulated using the PEP concept, as are their transmitters which are characterised by a certain peak power output at a certain level of distorsion or adjacent channel suppression.

    The Authorities have recognised amateur AM phone as the anachronism it is, and have used a power defintion that admittely is unsuited for it, instead of creating a special defintion for a mode they hope soon to be extinct (the hopes for extinction are sometimes extended to the other forms of amateur radio).
    I do not know the age distribution of AM:ers here, but in the US it seems largely to be populated by people in their 70s and 80s.

    The maximum power limits for amateur radio have historical reasons and have been arbitarily set for very good reasons.
    Amateur radio is operated just by amateurs, and we do not make any promises about circuit availability and reliability.
    We also do not promise coverage areas or user data throughputs.

    The Authorities may therefore set any power limits that they see fit. Amateur radio is in no position of demanding anything.
    Many amateurs still believe that they or their National Societies may demand privileges, but this has been proven wrong many times in recent years. If the power levels should be reduced by 10 or even 20 dB, the solution is to use Morse and moreover become a 10 or 20 dB better operator.

    The upcoming power reduction from 1000 to 200 W in Sweden is primarily derived from what the lawyers at the Regulator have learned about the lowered quality of the radio amateurs in recent years. They have not liked what they have seen, and they are consequently
    not considering the "Extra Class Novices" as competent of handling 1 kW power levels.

    Hopefully the requirements for the higher power authorisation permit discussed will be tough, such as an engineering degree or a First Class Radiotelegraph operator's certificate. This would restore some of our elite status that has previously been squandered by removing the Morse requirement and lowering the exam standards.

    73/
    Karl-Arne
    SM0AOM
     
    Last edited: May 26, 2018
  3. K3XR

    K3XR Ham Member QRZ Page

    That may be true in your country the AM broadcast band is alive and well at least in this area of the country. The Heathkit AJ 53 tuner and AA 14 amp are on in shack during at least some portion of most days.
     
  4. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Yep....for a symmetrical wave, the average voltage is zero. :)
     
    K4KYV likes this.
  5. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    I did work on a Doherty broadcast transmitter a couple of times back in the Pleistocene era. :)
     
  6. SM0AOM

    SM0AOM Ham Member QRZ Page

    All over Europe, AM broadcasting stations both on LF, MF and HF are closing due to the diminishing audiences and the high and increasing operating costs.

    LW broadcasts are operated only by few countries, one is Denmark that had to accommodate the needs for weather reports of their fishing fleet in the North Sea. Otherwise, most of the larger broadcasters have closed.

    The interest for AM sound broadcasting here is nil, there was a survey by our regulator about 10 years ago of selling spectrum cheaply for
    commercial broadcasts in the MF range, but there were no takers.

    People that love to hear the sound of their own voices usually do not have the financial means to operate radio stations, even if spectrum access would cost almost nothing.

    73/
    Karl-Arne
    SM0AOM
     
  7. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    AOM: The earliest use of the PEP definition I have found is in Dutch and German literature from the early and mid 1940's ("Hüllkurvenspitzenleistung"). The concept and definition were literally used in one of the power definitions in the 1947 ITU Radio Regulations, and a discussion of the subject is reported in the Conference Minutes at page 548 of http://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.62.51.en.107.pdf

    What page?

    [/QUOTE]

    "It is interesting to note that in two Historical texts from authoritative sources on Modulation Theory, (H.S. Black, Modulation Theory, Van Nostrand, 1953) and (A.B. Carlson, Communications Theory: An introduction to Signals and Noise in Electrical Communications, McGraw-Hill, 1968) PEP is never mentioned. In the Proceedings of the I.R.E. papers (forerunner of the IEEE) of 1956 there was a paper by George Grammer, Single Sideband in the Amateur Service and there no discussion of PEP to be found there as well. The same author also had an article in QST of 1954 on the comparison of DSB-AM and SSB and there was no mention of PEP. In the same year of the I.R.E. proceedings, Honey and Weaver produced an extensive analysis of SSB, but again there was no mention of PEP. A 1954 report from Collins Radio (in my files), written by Warren Bruene, Report on Single Sideband Techniques and Design Requirements, never mentioned PEP."

    You might show me where, in the above documents, that PEP is mentioned.


    Phil
     
  8. SM0AOM

    SM0AOM Ham Member QRZ Page

    It took only reading the second paragraph on page 9 of the Bruene report to find a reference to "peak envelope power". Not surprising, as Collins was an early proponent of the PEP concept.

    Other early papers and articles about SSB often used the term "peak power" interchangeably with PEP, but both terms came to carry the same definition in the ITU Radio Regulations. The "envelope" became a somewhat later formal addition, aimed to better visualise that the transmitted signal had an "envelope" around it, whose dimensions were used to compute the value of PEP.

    I believe that we have reached the "end of the road" in this matter, and I also find it highly unlikely that the FCC, or for that matter any spectrum Authority, will change their amateur radio power limits or power definitions just to accommodate a mode that will ultimately vanish by attrition.

    The moves by the German regulator to outlaw AM on the HF bands, are not that unexpected. The BundesNetzAgentur has a quite rigid, but also very practical stance in amateur radio regulatory matters. They want amateur radio to be progressive, and not clinging to anachronisms, but they also are the last bastion of traditionally regulated amateur radio in Europe.
    It remains to be seen if they also will succumb to the deregulation wave with its consequential disinterest in amateur radio that has spread over practically all regulators during the past two decades.


    73/
    Karl-Arne
    SM0AOM
     
  9. K4KYV

    K4KYV Subscriber QRZ Page

    Similarly, in response to deceptively inflated "peak power" ratings published by manufacturers and vendors of consumer-grade audio products, back in the 1970s the U.S. Federal Trade Commission enacted a regulation requiring that vendors of hi-fi audio and stereo amplifiers had to advertise their power output rating in terms of "RMS power" or "RMS watts". It took years to convince the regulators that this rule was bogus; there is no such thing as "RMS power" or "RMS watts".

    Sure, you can work through the equations and calculate the RMS value of the power of an a.c. waveform, but it has no physical significance. The meaningful quantity is average or mean power output, which does carry physical significance, describing the effective heating power of an a.c. wave, or the loudness/QRM generating power of a radio wave. What may be confusing to many is that average power = RMS voltage × RMS current. Average voltage × average current yields a physically meaningless number, just like the calculation of RMS power. By definition, average or mean power is RMS-derived, but this does not make it the same thing as "RMS power".
     
    KC8VWM likes this.
  10. K4KYV

    K4KYV Subscriber QRZ Page

    Yes, and this is true, even for an asymmetrical wave, if there is no rectification or non-linearity in the system. With the (usualy) highly asymmetrical human voice, the amplitude of peaks in one direction may exceed twice that of peaks in the opposite direction. But, the higher amplitude peaks are of proportionally shorter duration, while the lower amplitude peaks of the opposite polarity are of longer duration. When the waveform is drawn out on a graph, the area between the curve and base-line in both directions is equal, and the arithmetical sum of the two is zero. This is inherent to physics, and explains why a transformer or a series capacitor can readily pass AC but neither one can pass DC.

    A modulation transformer can pass the natural asymmetrical wave form of the human voice. But the so-called "ultramodulation", negative-cycle loading and negative peak clipping schemes artificially produce asymmetry in the waveform by partially rectifying the signal, usually with diodes and resistors. With an AM transmitter, this results in carrier shift, usually in the positive direction. With a faithfully amplified naturally asymmetrical human voice, if the modulator is capable of the required peak power output, modulation in the positive direction in excess of 100% produces no positive carrier shift.

    OTOH, configurations such as the popular class-E amplifier / pulse-width modulator combination are effectively DC coupled, and can carry the partially rectified signal all the way to the modulated stage, and the carrier shift will be observed. The DC input to the final will shift with modulation due to the partial rectification of the audio modulating the signal.
     

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