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PEP? Are Those Power Meters Showing Us PEP Peak Envelope Power, or just Peak Power?

Discussion in 'Amateur Radio Amplifiers' started by KQ4X, Dec 31, 2012.

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  1. KQ4X

    KQ4X QRZ Member QRZ Page

    Since FCC changed the rules years ago to say that maximum power of amateur stations is to not exceed 1,500 watts Peak Envelope Power / PEP OUT, I always wonder how we are supposed to know what our OUTPUT power is. (Previously, FCC set the maximum power to be measured at the INPUT of the final stage of amplification...something easy to do since we most always had meters showing the plate current and the plate voltage; the product of which would give us the INPUT power. Such as "not to exceed 1,000 watts INPUT".)

    I use a Heathkit SB-221 amp, and my only power meter is built into my MFJ Roller Inductor Tuner. That analog meter is showing me PEAK power, but I'm sure it is not displaying Peak ENVEOPE Power / PEP. Am I wrong?

    Are there any power meters built into equipment (like amps or tuners) that actually do tell you the PEP?

    I just don't see how the FCC can tell us to not exceed 1,500 PEP when we have no way of measuring it (short of expensive PEP meters).

    When I have my amp turned on, it might show 800 watts on the tuner power meter in the key down position. When I am on SSB does that mean I'm actually outputting twice that, or 1,600 watts PEP?

    Thanks. Warren KQ4X
  2. W1BR

    W1BR Premium Subscriber QRZ Page

    Your peak average power will be very close to the CW power level... the B+ sag may be a bit less with the dynamics of SSB duty, but PEP power is NEVER twice the average power output. 800 watts CW, maybe 900 watts SSB PEP average power.

  3. KQ4X

    KQ4X QRZ Member QRZ Page

    Thanks. I've never fully understood why the SB-221 says it is a "2 KW Linear Amplifier", unless it is implying that in the SSB mode (higher voltage AND higher plate amps) the amp is capable of INPUTTING 2,000 watts PEP to the finals. Which would yield approximately 1,300 watts or so PEP output.
  4. KQ4X

    KQ4X QRZ Member QRZ Page

    And thus the reason for my query. :) From what I've read, over and over, measuring actual PEP (output) is not an easy task; and the few meters I've seen advertised that actually DO that correctly are very expensive. That's why I doubted most ham meters (like on an amp or tuner) would have that expensive device installed; for it would greatly increase the price of the unit. Thanks again for your input.
  5. WG7X

    WG7X Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, that's correct. The whole "2 KW Linear Amplifier" is a bit of marketing hyperbole where they hoped that most people would assume that the output was 2kw, not that the input was 2kw. When that amp was designed and sold, the rules were written differently.

    Now we are allowed to simply measure output power instead of doing things the supposedly harder way.

    ...And yes, you need a true PEP meter or an oscilloscope to accurately measure your output. I think that only the real anal types would insist on using a scope. For our purposes a good PEP meter will work. Fortunately, the FCC feels the same way.

    73 Gary
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    The SB-220/-221 can't produce 1500W output. The plate transformer isn't capable. Even if it was, the HT (+3200V, NO load) isn't high enough for a pair of 3-500Z tubes (datasheet) to produce more than about 1200W in Class AB2 on any HF band. Buy a "PEP-reading wattmeter" if you want to, even though you don't need to.
  7. K7JEM

    K7JEM Ham Member QRZ Page

    The FCC rules don't require anyone to buy or acquire test equipment, they just require compliance with the rules. Most ham grade wattmeters are probably not extremely accurate, anyway.

  8. W1QJ

    W1QJ Ham Member QRZ Page

    For the most part this is true, but not 100%. In fact, looking at strict PEP power output one could get a 1500w peak ssb reading using an SB-220. You would have to increase the efficiency of the tank circuit a bit and perhaps up the drive power over 100 watts. The data sheet on a a 3-500 easily shows this tube can produce 750 watts output per tube. That is a 24/7 key down rating with proper cooling. In an SSB enviroment where short burts of output will not harm the tube, this tube(s) will easily produce more power. The SB-220 transformer is very capable of over 1A of current on peaks. SO providing the drive is available and the tank efficiency is high, the SB-220 supply will allow 1500 PEP operation. Pehaps not in contest voice keyer operation, but for DXing one could call at full legal output with an SB-220 operating optimally. I use a Post LP-100A digital readout PEP meter. After converting an SB-220 to 6 meters I will tune the input and output circuits to peak performance. With 100 watts drive I can load for max output and the power supply will sag and may give me a bit over 1300 watts key down. However, when testing on SSB the peaks will be well over 1500 PEP on the meter. SO this indicates that although the steady current cannot support 1500w but the peaks can be supported.
  9. W0UZR

    W0UZR Ham Member QRZ Page

    Just about what I was going to say. I almost bought a 221 amp that had a Peter Dahl transformer and a new beefier high voltage board in it and he guaranteed that it would key down at 2500 watts. And it would run all day at 1500 watts at a 60 watt drive. So unless you have an amp like that or an Alpha Delta or some other QRO amp that can key down at those kind of watts, then I wouldn't bother getting a PEP reading meter. I figure if my equipment cannot reach 1500 let alone going over that power, then I don't worry about any PEP reading. The most you can get out of your amp is probably around 1100/1200 watts.

    I have only run 300 watts out of my amp for several years now because when I crank it up to 1100/1200, the guy at the other end always says that he can't notice any increase in my signal.MAYBE a ½ of an S unit. He says that my audio gets a little louder, but that's all. So I just run 300 watts. Why cook the bejeepers out of my amp if no one is going to see an increase on their meter?
  10. G4LNA

    G4LNA Ham Member QRZ Page

    Why not just use an oscillioscope? Bit of calculation to work out the peak power, no need for any of those expensive meters.
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