Some QRP-Tests in JT65 through QO-100

  • Hello folks,


    I was curious what the estimated EIRP would be to be able to still receive a data signal through the satellite and I experimented a bit with the WSJT-X and JTDX-software.


    My setup: KX3 on 50 MHz (100mW) ==> 0 to 100 dB step attenuator ==> BU500 up-converter ==> filter ==> SG-Labs PA ==> 14m H-100 cable (approx. -7dB) ==> 5 turns helix ==> 1.8m offset dish (CAS 180).


    According to my measurements the entire setup is pretty linear, so that I can adjust the power accurately by using the 0 to 100 dB step attenuator between the KX3 and the BU500.


    I adjusted the power in a way that my reference power gives a signal that is at the same level as the lower CW beacon. According to some information that was distributed earlier, this corresponds to an EIRP of about 950 Watt (= 300mW into 3m dish in Bochum).


    I used a couple of modes but finally settled on JT65 to do my tests.


    Result: I can safely decode signals that are 35 dB below the maximum EIRP of the beacon signal, meaning, that an EIRP of only 300mW is sufficient to decode data signals. The table below shows some of the results. The fourth line was received with only 30 dB attenuation, equivalent to 950mW, the others with 35 dB attenuation = 300mW EIRP.



    Best 73


    Holger 'Geri', DK8KW




    1101 -20 1.0 888 # TEST DE DK8KW

    1103 -21 1.0 888 # TEST DE DK8KW

    1119 -22 1.1 890 # TEST DE DK8KW

    1123 -15 1.1 877 # TEST DE DK8KW

    1125 -21 1.1 878 # TEST DE DK8KW

    1127 -21 1.0 884 # TEST DE DK8KW

  • Hi Holger !


    Saw some of your tests today. I can confirm, that i am able to do FT4/FT8 QSO'S with only 200 mW from my DXPatrol MK3 upconverter. Lowest report was -03. So that would have been a good report on HF. Destroyed my PA, which is running only on one leg at the moment. Have to wait for the new LDMOS so i am stuck with FT4/FT8 and CW.


    Many thanks for your effort.


    73 Oliver

  • DL6KBG


    Hello Oliver,


    Thanks for confirmation on the possibility to run very very low power on the satellite and sorry to hear that you sccidently destroyed your PA. Happened to me a lot when I was active on 136 kHz some 20 years ago!


    The next test is that I want to use a small antenna with no gain, such as a kind of "groundplane" and confirm if I can detect my signal with this antenna and about 300mW PA output. In theory it should work.



    Vy 73 and see you in CW-QRP!


    Holger 'Geri'. DK8KW

  • OK Holger !


    The new LDMOS is on the way and also the SG-Labs PA. So i may prepared ;-)


    Most people using FT4/8 on QO-100 are running to much power. From HF we now it's still working down to -24 dB. That's someting to start, when no pa is available.


    Looking forward to your results.


    73 enjoy the rest of sunday.


    Oliver

  • OK Holger that was the first time today that made me smile. What a pleasure. Hpe i copied all right. Was it 10 mW in a 1.5 M Dish? Stunning. Let's do more cw. Have to check the filter settings in SDR-Console. Noise was much louder than your sigs. But, to copy.


    :-) cool 73 Oliver awdh

  • @DL6KGB


    Great, Oliver, that was fun. I had 20 dB attenuation in my transmitter chain, so around 6 to 10 mW into the 1.8m dish, equivalent to something like 10 Watt EIRP! I couuld copy your signal ufb, and I even got called by a 4z1-station.


    Some people say that life is too short for QRP, but I love it!



    Schönen Sonntagabend und vy 73!


    Holger 'Geri', DK8KW

  • Nice one, really. So it is possible to do. With one leg of the pa i had around 400-500mW into the 90cm Dish. Great.


    CW is cool. Until our next qso.


    vy 73 Oliver

  • It may be possible to use higher power in conjunction with the uplink signal of the tablet wifi antenna and directly use the LNB (no reflection focusing antenna) for testing...

  • Seems this is agood starting point for qso's. Mny tnx Zhaofeng for FT4 QSO. He reportet 100mW , me still with 400mW. Zhao used a 60cm Dish. Mine is 90.


    Was so dissapointed destroying my pa and at the end had so much fun.


    Tnx guys.


    73 Oliver

  • Hello all,


    Good old QRSS. I used to be one of the longwave 136 kHz pioneer back in the 90ies. At that time everybody told us that with our little antennas for the 2200m band we would not even reach the next village. It was the time befor JT65 and FT8 or WSPR. At that time we developed a very very slow type of CW (motto: "Longwave enthusiasts do it extremely slow").


    The principle is easy: you send CW signals with, for example, a dot length of 3 seconds and on the reception side you run a spectrogram software and let the naked eye do the decoding. The first LF transatlantic QSOs were made using QRSS.


    Today I remembered these good old times and thought that it might be worth to test QRSS on QO-100.


    This SPECTRAN screenshot shows a 3-second-dot QRSS signal, transmitted at 40dB below the beacon level. This corresponds to an EIRP of 95mW. The power at the feed of my 1.8m dish was 0.065mW!


    Explanation: the upper signals correspond to the dashes, the lower to the dots. You need a little bit of imagination to recognize my callsign: -.. -.- ---.. -.- .-- (DK8KW). Believe me, in the old LF-times we were used to read those faint signals from the screen right away, and we had fun QSOs over thousands of miles.


    It is fun now that QO-100 is there also for these (a little bit nostalgic) tests. And, by the way: QRSS beats JT65 by almost 5dB!



    Best 73


    Holger 'Geri', DK8KW




    Hi all,

  • Happy 136kHz days..........
    Is JT65 the optimum JT mode for weak signals on QO-100? Just wondering about small amounts of LO drift in the TX.
    Having said that, I suppose EME has doppler shift and all sorts of multipath distortion.

    73 David G0MRF (Still Txing on 475kHz and getting wspr reports and the odd QSO from The USA)

  • @G0MRF


    Hello David,


    Not sure if JT65 is indeed the best mode -- it was just a coincidence that I tested it first and it worked, after I had problems with FT8. My transmitter is not too stable and has frequency changes of a few Hz while transmitting (as can be seen on the QRSS-plot) and JT65 seems to be quite immune against those. FT8 is not that tolerant. I will do further tests in the future.


    Would love to come back to 136 and 472 kHz but at the moment my antenna is not sorted out (top load radials caught by branches of trees) and my shack is a mess -- have to find the equipment first.



    Best 73


    Holger 'Geri', DK8KW

  • The next day I actually measured the final power reaching the antenna.Only 5-6 DBM...