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Monday, May 18, 2015

BITX DIGI-TIA Build Update #3 Video of Receiver in Operation



A few things I forgot to mention in the video:

That USB port on the front panel has already come in handy.  I needed to switch the tuning increment from 1 kHz to 100 Hz.   I just went into the Arduino program, removed one zero, and then re-uploaded the code.  

I also put to use the sideband inversion rule-of-thumb:  My IF is at 9 MHz.  I want to receive signals in the 7.2 MHz range, and I want the VFO running ABOVE the IF frequency.  So obviously the VFO will be running at around 16.2 MHz.  So, rule-of-thumb time:  Will I be subtracting the frequency with modulation from the frequency without modulation?  Yes I will!  So, there will be sideband inversion.  This tells me where to position my BFO frequency.   The signals on 40 start out as Lower Sideband.  But as explained above, by the time they get to the filter they will be inverted and will be upper sideband signals.  So I need to put the BFO slightly BELOW the filter passband so that I can tune the signals in such a way as the sidebands fit into the filter passband and have the proper frequency relationship to the BFO to allow for demodulation. I put it at 8.9986 MHz.  With the Si5351, changes to the BFO and VFO frequencies are very easy.

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4 comments:

  1. Blush. Thanks for the (largely undeserved) kudos, Bill, and thanks for all the inspiration that you've provided me over the years. Good stuff.

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  2. Check out Tom AK2B's sketch for an Si5351 VFO if you haven't already. It allows changing the tuning increments with a simple tap of the rotary encoder. (Not sure whether it suits your other needs with the DIGI-TIA, however.)

    Jerry AA6KI
    Tucson

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  3. Can you do the SLB-1 Trick with the ADE-1. Which pins if you can please?

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    Replies
    1. I don't think you can. This is one of the advantages of the SBL-1. It has two pins on one of the coils. They are normally connected, but Pete Juliano put a 100 ohm pot in there and gave us a balance control.

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