FT8 Power, how much ????

Discussion in 'Working Different Modes' started by K4EM, Nov 12, 2017.

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  1. N2SUB

    N2SUB XML Subscriber QRZ Page

    That's the story of my life. :p
     
  2. N4MIT

    N4MIT XML Subscriber QRZ Page

    Unlock TX=RX (uncheck)
    Hold down the shift key
    Pick a clear spot to transmit
    Right Click

    Bingo! you transmit in one spot while listening in another... I use this technique all the time as I think I get heard more often by not calling on the DX stations pileup.
     
  3. N4MIT

    N4MIT XML Subscriber QRZ Page


    According to the manual for my FTDX5000mp "if you anticipate making data transmissions longer than a few minuets, we recommend reducing the transmitter power to 1/3 ~ 1/2 normal power. " With the transmit cycle being 12.6 seconds and the entire QSO typically taking less that 1 minute I would say you can run full smoke without any problem. I monitor the heatsink temp on mine and I've never seen over 110 degrees F at 200w and the fan cycles down during receive, so I know it cools down between transmit cycles. Typically if I can hear it, I can log it. Even with my crappy vertical antenna.
     
  4. N4MIT

    N4MIT XML Subscriber QRZ Page

  5. K2CQW

    K2CQW Ham Member QRZ Page

    How I do enjoy these theological discussions. To quote Billy Joel (gag), "All you need are looks and a whole lot of money."
     
  6. VA3VF

    VA3VF Ham Member QRZ Page

    Vince here would say: all you need is money, the best beautifier there is.:D
     
    K2CQW likes this.
  7. N4UP

    N4UP Premium Subscriber QRZ Page

    New to the mode, only 16 contacts ( 12 today, all on 17 meters ), but concerned about TX power.

    Running 10-20 watts to 10-element LPDA at 73 feet.

    14 of 16 reports SENT to others are above -05 with max of +20

    5 of 16 reports RCVD from others are above -05 but none above +01

    On average, my sent reports are almost always much higher than my received reports.

    Can I infer that I am simply hearing well, that those are not "massive" signals I am hearing? And that I am not "a disturbance in the force" ?? Or should I go to even lower power levels?

    With lots of band activity I have maybe 50% success rate in working stations I see calling CQ.
     
  8. N4UP

    N4UP Premium Subscriber QRZ Page

    Okay, so this may be a dead horse, but I am experimenting with power levels on FT8. I spent half the day at it, made 96 contacts and worked 40 countries ( alas, none of them new ). On each band, I started with 20 watts and worked who I could. Then I increased the power in stages up to 400 watts ( 200 watts on 30 meters ). At every power level increase I was able to work people who did not respond to me at a lower power level. No surprise. Clearly one can make contacts at low power, but to work virtually all the DX I could decode I needed moderate power levels ( 200-400 watts ). And this is all with fairly good antennas.

    The only "problem" is that from one contact to the next, I might be able to work someone at 20 watts and then for someone else I might need 400 watts. The signal strengths received do not usually indicate what power level I should use, because people don't hear ( decode ) the same. It doesn't make sense to me to try to adjust the power for every contact. Rather, if I am getting consistently "high" signal reports, then I can reduce the power some. And if I call someone who does not respond, I can increase the power level. The good news is that I worked everyone I wanted to without ever going over 400 watts, and in many cases less.

    To put it in percentages, at 40 watts my success rate was around 50%. At 400 watts my success rate was close to 100%.
     
  9. K6BRN

    K6BRN XML Subscriber QRZ Page

    Peter:

    What was your success rate at 1500 watts (OK... just kidding, there, could not resist)? :)

    Thank you for your experimental results. It's pretty much what would be expected, and from a single user standpoint says: "More power is better". That's often the case. But while FCC rules in general allow using the power needed to make the QSO, that one statement does not account for the RX overload that can impact other stations, some not even nearby, when using frequency slots spaced just a few Hz apart on convention-defined sub-bands just a few KHz wide.

    So that takes us into the realm of courtesy, which is not so easily defined and where argument reigns supreme.

    My personal thought is that a user should start out at relatively low power, say 25 watts out to a wire antenna (thinking of EIRP, here), then increase power to the point contacts can be made. If output power hits 100 watts - a convenient number given that most HF rigs will support this - stop and consider how crowded the sub-band is at the time and avoid disrupting many other contacts on that segment before switching on your not perfectly linear, linear amplifier and turning up the power. Because a linear amplifier at high output will not only overload the RX ends of other operators equipment with "OOB" signals, it will actually broaden your own signal significantly through its own IMD and other non-linear product contributions. "Significant" does NOT have to be much when we are using just a few Hz for signal separation and a couple of KHz for an entire sub-band.

    I'll let the other pundits sort out their own thoughts on this before I lean over, flip on the Quadra, turn it up to 1200 watts (way over its "good behavior limit"), wake up Zenki, and simply erase 40M FT8 for the evening, at least in North America.

    But when the band is dead and that lone DX contact shows up..... Ack! My amplifier trigger finger is twitching! The Quadra is glowing! Maybe just a LITTLE bit of power and 100 Hz or so more of bandwidth? (I can actually HEAR Joe Taylor and his crew banging their heads against the wall about now...) Too late, guys. Cats out of the bag.

    Brian - K6BRN
     
  10. N4UP

    N4UP Premium Subscriber QRZ Page

    Thank you for those insights. Yes, it would seem that more power is better, at times, and up to a point.

    I do not want to interfere with anyone, but how can I know if I my signal is a problem??

    I see a lot of signals over +05 ( some even +20 ) but I almost never receive a report over +05. I haven't been able to tell that anyone is interfering with anyone ! Yet clearly the FT8 "band" is crowded and sometimes there is need for a repeat, but I cannot yet "see" any offending signals, let alone my own. Maybe I should pay more attention to the waterfall. I grew up without waterfalls and prefer looking at my panadapter.
     

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