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ATS-4b DDS and BFO waveform questions

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  • Rob Steenburgh
    Greetings: I just completed the ATS-4b.   The rig appears to be working - I m receiving stations and getting RF out at 2W on all bands but 20m with about 8V
    Message 1 of 1 , Dec 21, 2011
    Greetings:

    I just completed the ATS-4b.   The rig appears to be working - I'm receiving stations and getting RF out at 2W on all bands but 20m with about 8V input.  I re-wound L18 in an attempt to squeeze a bit more out of 20m, but no luck yet.  Audio output seemed a bit low, but nothing I can't deal with.  However...

    I had some issues during the calibration process:
    • Getting the DDS to 10.000 MHz was tricky and may be due in part to the frequency counter I'm using or operator error.  While I was changing the frequency with the up/down buttons, the freq displayed on the counter was 10+ MHz, but when I let go of the button, it would settle back down to 9.9998 or so.  Eventually I was able to get it to land on 10.000 exactly.  Also, the frequency seemed to rise when pressing the down arrow, and fall when pressing the up arrow.  This was the opposite of what I expected.
    • When I looked at the waveform from TP1 on my oscilloscope, first it appeared as a sawtooth wave.  My probe was set at the x1 position.  When I switched to x10, it looked a bit more like a square wave, but with some noise at the top and bottom of each cycle.  I've attached a photo of the scope output.  Does this less than perfect square wave indicate something amiss?
    I moved on to the BFO step:
    • I could never get the BFO frequency to show up on the ATS display.  With the counter connected to TP2, I could land at approximately 625 Hz.
    • I hooked the scope up to TP2 expecting to see a sine wave but got something different - humps.  I've attached a picture of that, too.
    Yesterday, when I tested the xmit/rcv frequencies, they were spot-on until 20 and 15m when the varied by a few Hz.  Since I went through the whole calibration sequence a few times today, I need to go back and double check to make sure I'm still transmitting where I think I am.

    Are the peculiarities I've described above significant or not.  Should I worry; am I sacrificing performance or falling victim to obsessive-compulsive traits?

    73,
    Rob
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