100% Duty Cycle Non-repeaters?

Discussion in 'General Technical Questions and Answers' started by KE7RUX, Feb 13, 2020 at 8:25 AM.

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  1. KE7RUX

    KE7RUX Ham Member QRZ Page

    Is an 100% Duty Cycle only available with repeaters? Or is there some ham or commercial non-repeater equipment that have 100% Duty Cycle capability?
    73
     
  2. K9YLI

    K9YLI Ham Member QRZ Page

    A broadcast transmitter is 100% duty cycle. No logical reason to have any other with 100% cycle. And most repeaters that for a time run 100% are run at reduced power, the same as required for any cross band mobile or HT running as a repeater.
    I suppose a beacon runs at 100% but also at reduce power from its design capability.
     
  3. K7JEM

    K7JEM Ham Member QRZ Page

    Many, or most, transmitters can be run at 100% duty cycle, but usually not at full output power. I have some UHF mobile radios working as links, and they are 100% duty cycle. But we use a 25 watt radio set to 3 watts or so, even then it gets very hot, and we put fans on them to keep them cool. The heat sinks provided on most mobile equipment only assumes a 5-10% transmit duty cycle. Even older mobile radios, like the Micor (which had a huge heatsink) is only rated at 35 watts continuous, and realistically 25 watts would get pretty warm when keyed for an hour or more.
     
  4. W1VT

    W1VT Ham Member QRZ Page

    I'd design a lot of my homebrew gear for 100% duty cycle. I have a big heat sink on the back of my 3W 10GHz transverter. :)
     
  5. KV6O

    KV6O Ham Member QRZ Page

    You probably need to clarify a few things. Every radio I have runs 100% RX just fine. Most exciters can run 100% TX. It's the heat generating PA's that become quite expensive to run 100% at any reasonable power level.

    But there are few applications in the ham world that need to TX 100% of the time - what are you looking for?
     
  6. AG6QR

    AG6QR Premium Subscriber QRZ Page

    In the amateur service, we are generally required to listen for and avoid interference with other traffic. That can be difficult when transmitting at 100 percent duty cycle.

    But when you can legally achieve a high duty cycle, the main technical issue is basically one of heat dissipation. You can solve it by either reducing power or increasing cooling of the PA.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    What are you trying to do?
     
  8. KF5LJW

    KF5LJW Ham Member QRZ Page

    If you are talking 100% rated power @ 100% duty cycle, then yes repeaters and commercial equipment are about the only units capable of doing so out of the crate. None of the consumer grade ham rigs I know of are capable of doing that, and there is no need for it. Most would be not be able to afford it, and it would make both the rig and power supply much larger and heavier.

    Additionally ham rigs are made to modulate both on FM and AM modes. They use a linear amplifier which is required for AM but not FM which can use more efficient Class C amplifiers, thus not generating as much waste heat. FM repeaters have no use for AM, so they use Class C Amps making it much more economical and easier to run at 100% duty cycle.

    It can be done, and you can do it. But you HAVE TO MAKE ONE OF TWO SACRIFICES. Run TX power 6db down on your rig, or spend a lot more money on a much larger TX Amp and Power Supply . Take your pick.
     
    Last edited: Feb 13, 2020 at 6:21 PM
  9. K7TRF

    K7TRF Premium Subscriber QRZ Page

    As posted above there's quite a bit of commercial equipment designed to run at 100% duty cycles 24/7. Broadcast stations are one example, bent pipe transponders in satellites and corresponding earth to satellite stations supporting data networking or telecommunications run at 100% duty cycle and run continuously day in, day out. Many microwave point to point terrestrial links also run 100% duty cycle 24/7. Certain aircraft navigation beacons and other similar beacons also run at full rated power continuously.

    There are many commercial transmitters designed to run at full power without interruption for very long time periods but yes, it's not as common in amateur applications where most communications are half duplex and only one party transmits at a time.
     
  10. K8BZ

    K8BZ Ham Member QRZ Page

    The following is copied from the Icom web site on the IC-7600:

    High Power Final Amplifiers
    High-power FET transistors, RD100HHF1, are used in the PA unit providing excellent signal quality and low IMD characteristics. With a large heat sink and cooling fans, reliable 100W output at high duty cycle can be used, for example in contesting or data modes.

    They said 'high duty cycle' and didn't specifically say 100% duty cycle. However, I do contest in digital modes with the IC-7600 at full 100 watt output at 100% duty cycle while transmitting, and have never had a problem in over 10 years of doing so. But also know that contest calls and exchanges in digital modes are very short. So transmitting at 100w at 100% duty cycle for 5 seconds and then listening for 10 seconds is the same as transmitting continuously at 100w 33% duty cycle.

    In FM mode, which is 100% duty cycle the 7600 transmits at 100w. In AM mode the unmodulated carrier is 25 watts. But in AM, an over modulated (above 100% modulation) 25 watt carrier can have peaks in excess of 100w, thus, the reduced carrier power in AM mode.

    Update:
    The following is from the IC-7600 manual:

    ■ Transmitter
    • Output power (continuously adjustable)
    SSB/CW/RTTY/FM : Less than 2 to 100 W
    AM : Less than 1 to 30 W

    So it looks like the 7600 is capable of full power output at 100% duty cycle. But I would still consider it to be applicable for normal amateur transmitting time periods, and not 24/7 broadcasting.
     
    Last edited: Feb 14, 2020 at 5:02 PM

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