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A few FT-8 trickery for Yaesu (and other) radios.

Discussion in 'Working Different Modes' started by PY2RAF, Sep 19, 2019.

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  1. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hi there, list!

    I live in a big city with quite a few nearby (and QRO) fellow ham radio operators.

    So you are in the early morning, trying to take advantage of greyline propagation, you are almost working that China or Korean station when then suddenly... Well, that good nearby fellow ham radio operator starts operating at the same FT8 time slot of yours. What to do? Go to a quiet room and weep a bit? Cuss or curse the fellow operator?

    Nah. Work it out.

    I found two very useful tools in my FT-991A, which surely can be used by any modern transceiver. Namely: Notch Filter and Bandwidth Filter.

    NOTCH FILTER
    A picture is worth a thousand words. On the below scenario, I had PY2NF transmitting at the same time slot. Fortunately he was not hopping TX frequencies so I notched his signal - and was able to see the weaker signals again (pardon the portuguese annotations):
    [​IMG]

    During PY2NF silent period you can clearly see the smudge in the frequency that the notch filter caused. And then in the above "chico sem notch" annotation, at that moment I disabled the notch filter AGC kicked in and faded out with weak signals.

    DO NOT MISTAKE Notch Filter with "Autonotch" (usually, the DNF). The notch is a manual setting and you have to specify where to notch. Use the FT8 software frequency ruler to find out the approximate frequency and use the visual cue caused by the notching in the waterfall to put the notch perfectly over the undesired signal.

    ---
    BANDWIDTH FILTER
    This is a bit more laborious and takes a bit more of fiddling.
    By default, we will want the radio's front-end as wide as possible right, so we can see as much signal of interest as possible! That translate to usual 2.4 kHz to 3 kHz of bandwidth that is captured by your radio and rendered by the FT8 software.

    How do I manage to receive only that signal and getting rid of everything else?

    The BW filter might come to your rescue.
    First of all, you have to center your signal of interest to around 1 kHz. Of course the strong nearby signal will make your life harder so play with your estimates or you can also add or subtract to your VFO frequency.
    And finally, narrow down your bandwidth to get rid of the interfering signal! See the below picture:

    [​IMG]

    So, I moved the signal of interest to around 1 kHz, selected the Narrow bandwidth filter (500 Hz) and finally the interfering signal is entirely off the scope - and even more signals popped up.

    FT-991A settings:
    • Select the NAR/WIDE option to N
    • Tune the Width filter to 500 Hz
    [​IMG]

    ---

    OTHER GENERAL RECOMMENDATIONS
    • AGC: Use the fast one.
    • Noise Blanker: Turned out good results from me blanking out some interference
    • Amplifiers: Not of much help, no much (if any) oomph netted, because together with the signal, the noise is also amplified. However, a must in silent/higher bands. The quieter, the higher the amp gain (AMP1/AMP2)
    • Bandwidth filter: Normally wide. Use it to fish out that weak signal - this can provide several dBs of gain over faint signals if you go narrow, pulling signals out of the mud.
    • Width: Normally, you will want it as wide as possible. Work in tandem with Bandwidth filter.
    • Contour: Not of help, should be off
    • DNR: Avoid as it might distort the signal of interest, should be off
    • DNF (Autonotch): The DNF is meant to silence off signals with a constant carrier, such those dear fellas that tunes over a frequency that is in use. FT8 tends to be perceived as a offending signal and might be notched out thus this should remain off
    • Shift: Interesting to get rid of strong signals at the band edges. Should be at zero and used in a as-needed fashion.
    Hope that helps!

    Happy videobingoFT8ing,

    - Rodrigo, PY2RAF.
     
    Last edited by a moderator: Dec 17, 2019
    VK1FMGG, KT5WB and AD7DB like this.
  2. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    A few supporting evidence:

    [​IMG]

    Event sequence timeline:

    1. Station N4BP called me, MSHV reported -15 dB
    2. During the RX of N4BP I turned on the Narrow filter, reported signal jumped to -8 dB
    3. Finally, during that receiving slot entirely in Narrow filter, got the signal measured at 0 dB, w00t
    73 \o
     
    Last edited by a moderator: Dec 17, 2019
  3. ND6M

    ND6M Ham Member QRZ Page

    narrowing up the RX/notch filtering works quite well under certain conditions.

    Many people using FT8 keep their front end open to 4 or more Kc (in fact, the WSJT user guide recommends to do this), ........ and the they complain about being QRMed.

    same for any mode/signal. filters work great
     

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