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Re: [wsjtgroup] Laptop info

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  • Rex Moncur
    Hello Phil One warning about Laptops. In VK we have found that many Laptops do not generate the tones on the correct frequency and on JT44 this produces
    Message 1 of 5 , Nov 30, 2003
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      Hello  Phil
       
      One warning about Laptops.  In VK we have found that many Laptops do not generate the tones on the correct frequency and on JT44 this produces degraded performance on the tones further from the reference frequency e.g. Z.  We found this by TXing a message 1Z1Z1Z1Z1Z1Z1Z1Z1Z1Z on JT44 and counting the number of ZEDs and ONEs correctly decoded.  With weak signals typical performance at -21 dB to -23 dB was 80% correct ONES down to 40% ZEDS.
       
      After discussion this with Joe we have concluded that the problem is not only the fact that the higher tones get near the limits of the digital filters but that the timing of the tones is also out.
       
      The problem only shows up around -21 to -23 dB but this is where you want the best out of these modes.  The problem is not so obvious with JT65 but I expect it is still there - it is just disguised by the coding system (you don't know which tones are being used for different characters due to the FEC and coding).  Computer to computer tests show that poor laptops do not allow the JT65 special messages to be decoded even at good signal levels.
       
      There are a few ways to check a Laptop for this problem:
       
      1. Run it on FSK441 and measure the "D": test tone on a frequency counter which should be 2205 Hz within one or two Hz.  Many Laptops will read high by 8 to 15 Hz.
       
      2.TX between two computers using a direct audio connection on either JT44 or JT65 and measure the DF if it shows up at more than 1 Hz I would reject it.
       
      3. TX between two stations using FM and again the DF will show up the faulty Laptop.
       
      It seems that this problem only occurs on TX and all Laptops we have tested RX on frequency.  We have measured 8 desktops and all were on frequency to within 0.1 Hz.  Of the Laptops the more modern ones caused the problem typically 500 MHz and above with 6 showing errors of 8 or more Hz at the D test tone.  Older laptops tend to be better. In one case, a Dell Inspiron, it even changed tones after the first few seconds of each transmission and it seems this is due to the sound card implementation in software which changes frequency as a function of the workload on the CPU.
       
      73 Rex
      VK7MO
       
    • Art Jackson
      Hi Phil, If you plan to use it for Meteor Scatter only which is predominately FSK441 and little JT6M, a 266MHz laptop will work fine. JT65 takes alot more CPU
      Message 2 of 5 , Nov 30, 2003
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        Hi Phil,
        If you plan to use it for Meteor Scatter only which is predominately
        FSK441 and little JT6M, a 266MHz laptop will work fine.

        JT65 takes alot more CPU than JT44 did. Decodes take several times
        longer on my older CPU (166Mhz). Infact, I was not pleased. My old
        laptop is a workhorse on all the other modes. I also use it for all
        the other digital modes (PSK, RTTY and CW).

        JT65 runs fine on my newer computers (1 GHz+).
        You might want to try the laptop computer out as a Monitor and see
        what happens before you buy it.

        Good Luck
        Art

        --- In wsjtgroup@yahoogroups.com, "N0PB Phil" <n0pb@s...> wrote:
        > I am looking at purchasing a laptop to use mobile
      • David Robinson
        Phil I have been succesfully using the thinkpad 560X with 233M processor and 96M memory for the last couple of years with wsjt. It cost $82 on ebay. I use a
        Message 3 of 5 , Dec 1, 2003
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          Phil
           
          I have been succesfully using the thinkpad 560X with 233M processor and 96M memory for the last couple of years with wsjt. It cost $82 on ebay. I use a belkin usb to serial adaptor to control the PTT and use the onboard serial port to connect to a surplus $15 motorola UT+ and run Nmeatime to maintain timing. Nmeatime is vital as I find the time drifts under Windows 98SE. On my other 560X running win 95 i dont need it 
           
          Dave
           
          ww2r
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