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Again AM power , A new view

Discussion in 'Amplitude Modulation' started by WA1HLR, Mar 20, 2018.

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  1. WA1HLR

    WA1HLR Ham Member QRZ Page

    After stumbling into the AM forum I read Don K4KYV s AM power discussion. Being that the FCC is attempting to "level the playing field" with a 1500 watt PEP limit which we all know is NOT a one size fits all answer. As it is we can run 1500 watts PEP on DSB. It is well known that in the case of a 100% modulated AM emission the side bands are 6DB below that of the carrier. Therefore a 100 watt AM emission is 25 watts per side band OR 50 watts PEP total double side band. The 4:1 ratio of PEP to carrier is a system requirement to make AM happen. How is that so ? It can be explained mathematically which I do not have a clue. I did not go to engineering school. the term Amplitude Modulation is a misnomer. It is a mixing process of audio frequencies and the carrier frequency. In the mixing or, heterodyne process there are the sum and difference frequencies and the two originals. Only three of them make it out of the transmitter and into the antenna. The Upper and lower side bands and the carrier. One way of looking at it in the case of a 100 watt output transmitter. With typical efficiencies the dc input may be 130 watts to make 100 watts out. 65 watts of audio at the modulation peak is required. The class C stage is combining the audio power from the modulator into an AM emission at the plate efficiency of the stage ,assuming that it is modulating linearly. End result 50 watts PEP double side band with carrier. The perceived notion that 375 watts carrier at 100% modulation being 1500 watts pep is so in the making of an AM signal. The actual end result is 187 1/2 watts PEP DSB. A far cry from 1500 watts PEP SSB considering that it is 93.75 watts PEP per side band. In the case of malicious interference from an SSB operator running 1500 watts it's like bringing a knife to a gun fight. We have to ask ourselves why there is a power limit. It could be said to limit the potential interference one amateur may inflict on another. It could be a potential RF exposure limit who knows ? If AM is going to be competitive one must be able to run the equivalent power of 1500watts PEP DSB. That my friends is 3000 watts carrier power . The only sticking point is the carrier power.
    It's all about potential interference . Occupied band width that is. A carrier occupies no bandwidth. Today's modern SDR equipment can all but eliminate heterdyne interference. Even though I have plans of building a really Big Rig it probably will not be used much. Before the fire of '92 i had built a single 4-1000 modulated by a pair of 4-1000 s At full strap I ran 5500 Volts @ 450 Ma. Probably close to 2Kw out. Not all the time either.I have always believed in running the minimum amount of power to maintain the desired communications. Most of the time in the order of 100-150 watts out. Sometimes much less depending on the scenario. A typical 3Kw big rig could be a 5Kw plate modulated broadcast transmitter. These boxes operate on 3 phase power. By utilizing two sections of the plate transformer and a few other power supply mods, more inductance of the filter reactor and more output capacity the typical plate voltage of a three phase supply is in the order of 5Kv with most of the plate modulate 5& 10 kw rigs. In single phase mode expect 2/3 the output voltage @ 2/3 current capacity or a little more than 3-1/2 Kv. Just right for a full 1500 watt PEP DSB power. Think about it.
    Tim WA1HnyLR
    KM1H likes this.
  2. W2VW

    W2VW XML Subscriber QRZ Page

    My big rig runs 150 watts of filament emission in the final and that works fine.
  3. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Here is my response sent to the FCC before the deadline on simplifying the rules for
    ET Docket 17-215:

    "IV. Suggestions for Simplification and Clarification of Part 97 Power Rules
    In view of the above, the following wording is suggested in order to simplify Part 97.313, and to affect an equitable set of power standards for all modes.

    § 97.313 Transmitter Power Standards:
    (a) An amateur station must use the minimum transmitter power necessary to carry out the desired communications.
    (b) where expressed as radio frequency output power measured across an impedance matched load,
    (i) 3000 W peak envelope power for transmitters that produce any type of sideband emission(s), or
    (ii) 1500 W carrier power for transmitters that produce any other type of emission..."


    Attached Files:

    Last edited: Mar 20, 2018
  4. N2DTS

    N2DTS Ham Member QRZ Page

    What does it matter?
    No one cares how much power you run or how wide your signal is.
    My big rig used to run 600 or 700 watts of carrier and be fully modulated.
    RF power supply on one 120 volt phase, the modulator on another.
    Its now set up to run 400 watts carrier on a common supply.
    90% of the time I run 300 watts or less.
    You told me a while ago Tim that if you run a strong signal, you have to talk to piss weak guys and its true.

    Who knows anyway, a low power signal into a good antenna or a directional antenna, or a lot of power into a poor low antenna.
    How would you measure it remotely?

    My antenna is poor, so I could run 600 watts carrier and no one would know I was running a KW over legal limit.
  5. K5UJ

    K5UJ Ham Member QRZ Page

    I've read this AM / slopbucket comparison re effective power before but I'm glad to have it in an easy to find location. It shows among other things, how AM ops got taken to the cleaners by Johnston when the power limit rule went into effect. The irony is a slopbucketeer with an over driven plastic radio, over driving a cheap 1 KW solid state leenyar, can create a lot more misery on a ham band than can a clean peak limited 1000 w. AM rig with a 4 or 5 kc audio response. Be a good op, run a good rig, and some power measurement inaccuracy is about like having a speedometer that reads 10 mph low.

    What's your antenna? Maybe we can help.
  6. N1BCG

    N1BCG Ham Member QRZ Page

    In the b’cast world, this would require removing the power measurement device (ex: AM antenna ammeter, FM Bird wattmeter), switching to the “indirect method” of power measurement, and notifying the FCC in writing. You now have 30 days to get the device fixed.

    The alternative includes heavy fines for the station and a possible firing for the engineer.

    Further proof of the vast chasm between professional and hamateur radio.
  7. N2DTS

    N2DTS Ham Member QRZ Page

    This seems very much like a holdover from when it might have mattered.
    Is there any enforcement these days?

  8. N2DTS

    N2DTS Ham Member QRZ Page

    80/40 meter fan dipole up about 40 feet in the tree's over poor ground soil.
    No room for anything better, a tower would help.

    Some guys run a big antenna on top of two tall towers, or on top of a mountain...

    What's your antenna? Maybe we can help.[/QUOTE]
  9. K5UJ

    K5UJ Ham Member QRZ Page

    What's the point being made here?

    I recommend an 80 meter center fed dipole, fed with OWL and a KW Matchbox or other link tuner, and try a grounded screen under the dipole. No data to support this but I have my 160 m. ground system under my 80 m. dipole which is not much higher than yours and I usually get fairly good sig. reports within cloud burner range.
  10. WB2CAU

    WB2CAU Ham Member QRZ Page

    To me, it doesn't matter how you twist the interpretation of the 1500W PEP rule for AM. What matters is how the FCC measures it during an inspection of your station, if it ever came to that, which as far as I know happens extremely rarely. I always assume it's their equipment you have to comply with.

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