DDS VFO settings?

Discussion in 'Homebrew and Kit Projects' started by KC8MWG, Apr 1, 2016.

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  1. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I haven't gone through the Klopik schematics and diagrams to account for all the processing stages or the exact frequencies or how filtering is managed at the front end or the IF but it would look something like this:

    block diagram.png
    sketch something like this following the actual stage by stage processing from the Klopik documentation. This would be for the receive chain and the transmit chain would be similar but backwards starting from signal generation at IF and then conversion and RF amplification to the antenna.

    Sketch a diagram like this and plug in frequencies from the email you received. For instance for 3.5 MHz at the antenna the VFO would have to be tuned to 12.367 MHz such that the difference translates the incoming RF signal to the IF frequency. Then the BFO beats a crystal oscillator at that same IF frequency(or very near it if the BFO is tuneable for receive pitch adjustment on CW) and the signal is converted down to baseband audio via the product detector (the second mixer in the schematic which is driven by the BFO oscillator below it in the schematic), the audio is amplified and sent to a speaker or headphones.

    That's the basic block diagram of a single conversion receiver like your Klopik, there can be variations in filter and amplification stages but that's the basic structure. Use that to understand how different filtering and different VFO frequencies let you translate RF signals all the way down to baseband and filter out unwanted signals including image products out of the mixers.

    -Dave
    P.S. To really understand things try to figure out what happens to both the desired and undesired mixing products out of each mixer. The mixers create sum and difference products so figure out which one you're interested in and which one is an undesired image and how the receive structure and filtering help you deal with those issues.
     
    Last edited: Apr 2, 2016
  2. G1VQI

    G1VQI Ham Member QRZ Page

    I bought this kit and had the same problems, even had to rewind the coils as the first time it wasnt clear they were bifilar or trifilar and twisted together ,( as a first build this needed explaining ) i got rid of that terrible wire they supply and used .1 instead if i recall..The Kit is advertised as ideal for a novice on ebay , which is misleading . Shame the instructions are not written as well as the adverrt. As for basic support , nah...
     
    Last edited: Jun 29, 2020
  3. G1VQI

    G1VQI Ham Member QRZ Page

    upgraded slightly instructions
     

    Attached Files:

  4. N7EKU

    N7EKU Ham Member QRZ Page

    Hi,

    Who did the instructions update? Was that from the seller?

    As far as the VFO goes, it's up to you to choose the injection frequency. As it's single conversion and broadband, you can do high side or low side. What matters is where the mixing spurs will occur. So you would be wise to run the options through a mixing spur program (there are lots on the web), or do the calculations yourself in a spreadsheet, to see if any issues occur with your choice.

    If you don't know this area of radio operation, you should study up on it as it's important for anyone making their own rig capable of transmitting.

    73,


    Mark
     
  5. G1VQI

    G1VQI Ham Member QRZ Page

    Yes that was from the seller after I pestered him for better instructions
     

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