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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. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The Heath meter is a good deal and works well. Like all "monimatch" type circuits, it can be calibrated to be very accurate at full scale into a perfect 50 Ohm load. And like all similar circuits, once the termination isn't 50 Ohms, the power readings will be off.:p Same holds true for the Bird Thruline.

    Two pretty inexpensive but reasonably accurate and easy to use true PEP meters for HF are the Autek WM-1 and the Ameritron AWM-30. I like the WM-1 better (although it's larger) because it indicates forward power on one large meter and directly reads SWR on another large meter; so no switches, no squinting to see where needles cross, etc. It's a good circuit, and they have a patent on it. It also only about $159 brand new. There are several others on the market, including some which include only a coupler and software and use your computer to run the algorithms for SWR and display the results. I've used the Wavenode units (I was a Beta site for them when the product was in development and still have a prototype) and they are very, very good -- although they do require a USB connection to your computer.

    I have never in my life heard of the FCC citing anyone for running excessive power in the ham bands. It's probably happened, but I've never heard of it.:eek:
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    Over the decades, there have been notices when an amateur radio operator was running power above the legal limit that have been published in QST, CQ, etc. There have also been notices where an operator was reported by other amateur radio operators as to be running above the legal limit where it was determined by the FCC not to be true. In those cases, there was a very good antenna system involved and, although the effective radiated power was high, the actual power delivered into the antenna was well within legal limits.

    Glen, K9STH
  3. KV6O

    KV6O Ham Member QRZ Page

    Take a deep breath - we're all having a conversation.

    Part 97.313 defines Transmitter Power Standards, and specifically refers to Peak Envelope Power. Not watt meters (peak reading, RMS, average, etc.) - it just refers to PEP as the standard. Using a wattmeter to determine your power is one way of keeping in compliance, but your have to know what you're reading, which the OP was asking about. So are a bunch of other methods. For example Automatic Power Control is not used much in the ham world, but cell phone communication as we know it couldn't exist without it. If I were to implement an APC system on my legal capable HF amplifier, that would be one method of maintaining compliance with Part 97 without using a watt meter. Arguably, this would be a better method as the system would be real-time and automatic - using a watt meter requires the operator to complete the feedback loop and (arguably) could lead to power excursions outside the limits easily and frequently, while an APC system would not.

  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Glen, I've heard of such notices a few times over 47+ years in ham radio, but I don't recall anyone actually paying any sort of forfeit or being formally charged with the violation. Again, in all this time it's probably happened, but I can't recall it ever happening.

    I do recall Henry building amps many years ago that were easily capable of exceeding the legal amateur (U.S.) limit. They were "export" models. If a U.S. based ham bought one, they'd include a grid current trip circuit that would kick the amp off line if grid current exceeded some value, above which the amp could be driven to illegal power. I'm sure that could be defeated, but at least the intentions were good.:p An SB-220 can't run illegal power on the bands it was designed for, so I wouldn't worry about that one.:eek:

    The only ham I knew personally who was paid a visit by FCC field engineers after having complaints of illegal power lodged against him was W2ONV in NJ. I knew Bill pretty well and had visited his shack several times. He had a homebrew 4-1000A in GG and only 4000V on it, and it could just barely hit 1500W output.

    The FCC did visit, found that was the only amp he had, and told the complainers to please stop complaining. His big signal on 20m was due to stacked 20m monobanders on his Sky Needle tower, probably aided by very good soil conductivity in his area (low and swampy, but an area chosen by some AM BC stations for that small advantage).
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    If I remember correctly, some of those running excessive power were given a choice of either turning in their amateur radio operator's license or paying a large fine. Most just turned in their license.

    Glen, K9STH
  6. KQ4X

    KQ4X Ham Member QRZ Page

    So...back to my original question: I have an MFJ Roller Inductor Tuner, Model 989C. I includes a cross needle meter, showing Forward and Reflected power and SWR.

    The forward reading POWER can be switched (with buttons) to show either " PEAK" or "AVG". QUESTION: In that "PEAK" mode is it actually showing me "PEAK ENVELOPE POWER - PEP" when I am in SSB voice mode? (Regardless of how accurate it might be.)
  7. K7JEM

    K7JEM Ham Member QRZ Page

    Maybe, maybe not. According to the manual, on average voice it will only be reading about 70% of the PEP. So, 1400W PEP might only read 1000 on the meter.

    If you insert a two tone test, then it might be closer. But voice will just not read accurately on this meter, will always show low. The peak switch just inserts a capacitor to change how fast the needle falls.

  8. W1BR

    W1BR Premium Subscriber QRZ Page

    And any audio or RF processing will affect the reading as well.

  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Most accurately stated: The meter in the tuner is absolutely not a true PEP wattmeter, period. It isn't.

    It only adds a long decay time to a standard diode detector, so the meter needles don't fall as quickly. But it's not a true PEP meter.

    Ameritron does make a true PEP meter, the AWM-30. They built that circuit into the AL-80B amplifier, and it tracks almost exactly with my other true PEP meters. One way to tell:

    Run constant-carrier, key down, for a few seconds and observe the output meter reading.

    Then, use CW to send just a dit and observe the reading. With one "dit."

    With a real PEP meter, they will read the same thing, or the "dit" might read very slightly higher because there's less power supply sag from a dit than from a long carrier. But usually, the readings will be almost identical. They are on my PEP meters.

    If they are not, it's not really reading PEP.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I agree. But I didn't say that was a way to determine accuracy. It's a simple test to help establish whether the meter circuit is really a PEP type or not. They all require a source of DC power as they use active circuits which require power and can't operate just from rectified RF.

    Accuracy is another subject. The Autek circuit in the WM-1 is quite good and even includes an ASIC with embedded firmware to continuously calculate SWR and display that on a separate meter (as opposed to just indicating F and R and leaving it up to you to calculate SWR, such as in the simple Bird Thruline analog instruments, or crossed needles like Ameritron uses).
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