FT8 signal report levels

Discussion in 'Working Different Modes' started by N3DT, Nov 10, 2017.

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  1. N3DT

    N3DT Ham Member QRZ Page

    Been playing with FT8 a bit mostly on 12 & 15. Got a lot of SA contacts, but what is curious to me is that I seem to give them reports of about 10 dB more than they give me. Don't think my antennas are any slouch, H DoubleBays and I'm running about 18W out of the TS2000, the H is certainly better than the 70' dipoles at least on RX. Is this typical or are these guys running 100W, they mostly put a big red line on the waterfall. I'm talking about giving them reports in the + and mine are mostly in the -.
     
  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    1. The dB numbers are an artificial manipulated figure and don't represent actual signal strength to a calibrated meter.

    2. The figure is affected by local noise, type of antenna, adjacent signals and even filter width.

    3. Yes, I very often have significant split in Sent/Received figure.

    Don't worry, you aren't doing anything wrong.
     
  3. W1VT

    W1VT Ham Member QRZ Page

    I assume the difference is due to the pileups they generate. There are relatively few SA stations and a lot more NA stations, so their passband is filled with NA stations you can't hear.
     
  4. N3DT

    N3DT Ham Member QRZ Page

    I thought the numbers were S/N ratios, who has a calibrated antenna/RX anyhow in Hamdom? Now if they're good S/N numbers I haven't any way of knowing. At least they seem to correspond to the relative strength of the displayed signal with some consistency. I'm not going to worry about it, I was just wondering of others experiences and if it's typical? Thanks.
     
  5. VA3VF

    VA3VF Ham Member QRZ Page

    The info is in the manual. The calculation is not the same as with other modes. It does not even reflect an entire 15 second cycle, if propagation changes abruptly. I don't remember now if it reports the highest or the lowest signal during the cycle.
     
  6. G0JUR

    G0JUR Ham Member QRZ Page

    They may well be running 100 watts, its been decided FT8 is a weak signal mode but not a low power mode, (which explains some of the signals seen)
     
    WG7X likes this.
  7. G3YRO

    G3YRO Ham Member QRZ Page

    To me, it's one of the many silly things about these computer-based modes . . .

    It's how much your signal is above the person's noise level at the other end, not your actual signal strength.

    So it all depends on the other person's noise level.

    If you are S9 with them, but their noise level is S8, your report will only be 6dB higher.

    But if your noise level is S4 and they are S9 with you, there report from you will be 30dB higher !

    Roger G3YRO
     
  8. W4NNF

    W4NNF XML Subscriber QRZ Page

    There are many things that can affect the report you get...propagation...modulation level...noise at the receiving end...power you are running...etc., etc., etc. If you're consistently getting lower signal reports than you are sending, you might want to do some checking.
     
  9. N3DT

    N3DT Ham Member QRZ Page

    My first experience must have been an aberration. It's not like that any more.
     
  10. N3DT

    N3DT Ham Member QRZ Page

    I'm getting paranoid again. I have a total of 39 FT8 contacts now and I calculated the average of the difference between received report and sent report and I get -10. That is, the average of all my contacts have a S/N 10dB worse than what I send. Anyone else notice this? I've been running 20W. Once in a while I get better reports than I send and once in a while they're about the same, but the bulk of them are negative? I don't seem to have problems making contacts unless the other guy's timing is way off which I notice once in a while.
     

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