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Re: [FUNcube] M1GEO HF Upconverter Design

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  • Alan Melia
    Hi George You seem to have the test equipment. .....have you measured the IMD products of the combination?? I can t believe the funcube will work all that well
    Message 1 of 34 , Sep 25, 2011
      Hi George You seem to have the test equipment. .....have you measured the
      IMD products of the combination?? I can't believe the funcube will work all
      that well being hit by a not very reduced 100MHz LO?? -50dB LO feed through
      from a +7dBm LO means hitting the FCD with about 20mV , and the IMD
      performance of the FCD is adequate but not too good. Just a thought rather
      than be disappointed .

      Alan G3NYK

      ----- Original Message -----
      From: "George" <george.smart1@...>
      To: <funcube@...>
      Sent: Sunday, September 25, 2011 11:22 PM
      Subject: [FUNcube] M1GEO HF Upconverter Design


      > Hi.
      >
      > Just to anybody who is interested, I have designed an up-converter for HF
      using readily available parts. I have also published the schematic & PCB
      for anyone wishing to make one.
      >
      > http://www.george-smart.co.uk/wiki/FunCube_Upconverter
      >
      > I intend to add diode-switching to a later design, allowing the
      up-converter to be switched in and out electronically.
      >
      > Just thought my work may save someone else the effort.
      >
      > Cheers.
      >
      > George, M1GEO.
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >
    • f6itu
      ... Hi Georges May I suggest you a small and very stupid enhancement to your nice universal upconverter ? I build something very close to your design. I just
      Message 34 of 34 , Aug 3, 2012
        >...I have designed an up-converter for HF using readily available parts.

        Hi Georges

        May I suggest you a small and very stupid enhancement to your nice "universal upconverter" ?

        I build something very close to your design. I just added a "smoothing" Pi low path filter" on the oscillator output to reduce harmonics due to the "square" nature of the signal, and added a very soft high path on the output as you mentioned it on your blog. But this is not the point.

        I used a 3.3 V oscillator and was unable to hear anything on the output of the transverter. Even with a signal generator injecting more thant -40 dBm on the input filter...

        After some search, I found that the level of the LO input at the mixer input was 0.2 dBm... far too low. But when I disconected the mixer's input from the OL trace, the level of the oscillator jumped back to it's original power(around 12 dBm). I discovered that some oscillators cannot suffer a electrical grounding of their output (and the transformer of the LO input acts as a DC grounding)

        It took me half a day to find this gremlin. The solution is quite simple : just add a series 300 pf cap (or whatever) after the attenuator and before the mixer, it will cut the DC junction and you'll find your 7 dBm signal back again.

        Even if most TTL oscillators don't need such a precaution, adding this cap won't cause any trouble... and will avoid newcomers to search the reason why this +@!%**ing oscillator is down.

        Thanks for sharing your experience, Georges
        Hope this will help

        73'
        Marc f6itu
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