An Opensource Mini-Whip Antenna and Upconverter Design for RTL-SDRs

Thank you to Igor Yatsevich for submitting news about an open source Mini-Whip and Upconverter design that he's created and released for free on GitHub. An upconverter converts HF frequencies into VHF frequencies so that they can be received by RTL-SDRs in their quadrature mode, and a Mini-Whip is a small active antenna for receiving HF signals.

The designs include the PCB Gerber files for manufacturing, the components list and assembly and usage guides. Also both through-hole and SMD designs are provided.

The Mini-Whip design has a frequency range of 10 kHz - 30 MHz and to power it you'll need a 5 - 13V bias tee. You will need to install it up high and preferably away from the house as Mini-Whips are quite susceptible to local noise pickup. Another very important point is that Mini-Whips need to have a good ground connection. The upconverter is based on the ADE-1 mixer, and uses a 125 MHz local oscillator.

Igor's documentation on the project is excellent, and is a good read for getting more information about upconverters and Mini-Whips. He has noted that he is sending us some samples of units that he's built, so when we receive them we'll post again with test results. It looks as if he's put a lot of research into these designs so we're looking forward to seeing how well they work. 

Diagram on how to ground a miniwhip connected to a metal mast.
Diagram from Igor's documentation about how to properly ground a Mini-Whip connected to a metal mast.

14 comments

  1. John

    The J310 is getting a bit expensive these days, I have tried a 2N5486 which works just the same and is much cheaper ($0.98)

  2. jlc66

    Ah, the mini-whip. It always seemed to me like soup from a stone. You only need this very small piece of metal. It just has to be high up, at the top of a long piece of wire. People have modeled it, and, indeed, the long wire (coax) serves as the antenna.

  3. Dan

    I don’t suppose any of the people slamming the PA0RDT will care to point to some case studies?

    At any rate, the article is also about the upconverter. There are many diode mixer designs like this out there and they do work. It’s very convenient these can be ordered from jclpcb for very cheap straight from the public EasyEDA project.

    • Mike

      Ok, here I am “publishing” a study anyone can reproduce.
      Setup 1 is a vertical 24AWG wire going up along a 30ft fiberglass pole. There is a 8ft ground rod near the base of the pole. The wire and the ground are connected to a 1:1 transformer (4 turns bifillar on BN43-202 binocular ferrite core). The other side of the transformer is connected to coax going to the shack. The coax shield is also tied to the ground rod.
      Setup 2 is a mini-whip mounted on top of the same pole. The coax from the mini-whip is connected at the base to the coax going to the shack, without the transformer, but with the shield grounded at the base to the same rod.
      I claim that there is no observable difference in the S/N ratio of these 2 setups. Prove me wrong.
      For completeness, setup 3: FT-817 radio on the asphalt shingle / wood frame house roof, 6m up, connected to a battery supplied mini-whip with a 1ft piece of coax. No connection to any kind of ground. This setup can only receive the strongest signals and is basically unusable. I claim (and mini-whip proponents don’t deny) that mini-whip REQUIRES a long vertical feedline grounded at the base to work at all.

  4. Kerteszradio

    It is really incredible. Here is a shematics : http://radioaficion.com/cms/pa0rdt-mini-whip/ Suggest replace the J310 to MPF102. This slightly better (lower) noise. All data in millimeter. I replace the “probe” antenna to 60cm wire antenna but not much better. Of contrary ! These setup in occasional overloaded the V3 dongle direct sampling input.

  5. Rusty

    Stop spruiking this snake oil. It has been repeatedly proven that mini whips are no more effective than the length of the feedline.

    • Max

      This is partially true but if somebody can turn a vertical feedline into a good receiving antenna just using a simple amplifier he is already a genius.
      The results can be seen at Twente websdr, it’s true, not a metropolitan legend.

      • Anonymous

        When in a quiet place, mini-whip works similar to a vertical (wire, not coax) of the same length as the feedline. This is my real experience. The amplifier doesn’t change the S/N ratio on most of HF bands, and is prone to overload. So the simple vertical without the amplifier has some advantage when strong signals are present. Both systems require good clean ground.
        So yes, mini-whip really works, and no, it doesn’t work better than a piece of wire in the same location. The only situation where it works better is with a deaf receiver which benefits from the preamp gain.

      • Adam

        If I do remember well, the antenna on Twente websdr is placed on top of the uilding where the roof is flat and completely covered with the metal sheet. This brings another dimension to this antenna but comparing it to the proper wire antennas is out of the question.

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