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146MHz DATV 2-way 28km



    Cluster Activity

    Spots per uW band today:
    UK spotter or spotted only.

    Solar data:
    SFI
    76
    A-Index
    6
    K-Index
    2
    Exp.K
    2
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    26
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    qui
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    qui
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    My Weather

    Date:18/11/17 Time:17:38
    Temp:3C
    Wind Speed:0mph
    Wind Dir:270deg
    Pressure:1017.19mB
    Humidity:118%
    Dew Point:6.6C
    UKHASnet
    146MHz DATV 2-way 28km

    DX News!

    On January 11th Terry G1LPS and myself completed the first 2-way DATV QSO on the 2m band!

    Here are some video's of Terry's signal:




    Previous to this there has been two 1-way contacts at about 4km (G0WFT and G3KKD) and 237km from F9ZG and F3YX with a different experimental permit.

    There was a slight drop in the winds so we could raise the antennas up to clear the rooftops and the signal came through with minimal effort - approx 15-20dB MER on the 28km path.
    My rx seemed to be working better that Terry's but that maybe due to less local noise or possibly stronger nearby interfering signals at Terry's end - we are looking into this a bit more to find out why, could be a filter off tune...

    We both used around 1Watt from the RD06/RD15 amplifiers and Yagi antennas - see the station information on the previous 146 page.
    We used 333Ks once again and MPEG4 video.
    Terry used my script to re-encode the MPEG2 video from the hauppauge capture card into MPEG4.
    I was using the raspberry pi camera as the MPEG4 video source (no audio) and using the UglyDATV disk image (by Evariste F5OEO) but with the express_server software installed so i could use the DATV Express as the Tx, the pi was running at about 25% cpu usage. Is there enough left to encode mpeg2 audio from a usb soundcard? - not tested yet...

    Looking on an SDR shows Terry's signal about 25dB over the noise, the MER was reading 15-20dB, i presume this is related to the drop in performance of the pci card demodulator at lower symbol rates because the tx/amp are running in a very linear state.

    G1LPS Spectrum



    G1LPS Tutioune Rx




    We have done some basic comparisons between the Techno trend 1600 and 3200 cards with a weak signal, so far they both appear to lock a weak signal at 333Ks as good as each other.
    We have not tested lower symbol rates yet where the 1600 card may have an advange as others suggest but so far they seem to decode quite simlar.
    The two cards do report quite different MER when the bit error rates are reporting very similar results.

    Top is 1600 Card, below is 3200 card:

    Tutioune COmparison 1600 vs 3200 at 333Ks






    The next plan is to try for longer dx >100km :-)
    One path plot above 100km has been simulated as having roughly 20dB more path loss than the 28km path so it should be possible.
    This is from two portable sites so should have much lower receiver noise due to the remote locations at either end.

    A possible sea path is the one i used for the 117km Optical QSO a few years back, that was from Danby Beacon on the east coast to near Alnwick.







    Last page added:16/08/17 15:45
    M0DTS.co.uk