Connecting an RTL-SDR Panadapter to a uBITX Transceiver

The uBITX is a US$129 HF SSB/CW QRP transceiver kit that works from 3 MHz to 30 MHz with up to 10W TX power. It's a fully analogue radio, but it can be combined with an RTL-SDR to create a panadapter display thanks to a tutorial released by KD8CEC.

The method requires that you use the custom CEC firmware, or modify other firmware,  as this appears to change the output frequency at the tap point. The tap point is made accessible by soldering on an extra SMA connector for the RTL-SDR to connect to. The rest of the work is entirely performed in the uBITX software manager, Omni-Rig and SDR-Console V3.

uBITX with RTL-SDR Panadapter
uBITX with RTL-SDR Panadapter

8 comments

  1. Drone

    The article source location has unreasonable restrictions on commenting, so I’ll drop this here:

    “Pan-Adapters” are sometimes referred to as “PAIN-Adapters”, especially if you use a SDR. There are good reasons for this…

    1. Many SDR’s radiate out the antenna port (especially direct conversion SDR’s). An SDR without a front-end amplifier, and/or directional isolator may struggle with unwanted signal leakage out the antenna port. This can cause real problems when you connect the SDR to your radio’s IF, especially if your radio is a transceiver with a shared transmit/receive IF.

    You have to be careful with this. If you don’t you may (at-least) transmit unwanted signals. Isolating the SDR from the IF is best done using a high isolation physical relay or seitch that not only isolates the SDR input during transmit, it terminates it. Also to avoid unwanted double termination, the relay or switch should be a break-before-make type.

    Even with a physical switch or relay you may find your isolation isn’t good enough and you will need to add more shielding, capacitor bypassing, and/or series chokes at critical points. Remember, a non-isolated SDR connection may not only be a source of unwanted radiation, it may also act as a feedback path that causes instability.

    2. Tapping the lower IF frequency will result in less unwanted signal products during receive, but more during transmit. The opposite is true for tapping the high IF.

    3. Simply connecting the SDR to the IF chain will cause an unwanted impedance mismatch. Buffer or pad the connection to reduce this effect.

    4. Depending on your system design and type of SDR (down conversion or direct conversion), sometimes a diplexer can be used to good effect to isolate unwanted signals and impedance mismatches introduced by the SDR.

  2. SDRnoob

    I have a couple of these RTLSDRs and other than use as a receiver I did not know they had any other potential uses. Is there a list/site/reference online that will outline the other uses?

    • Drone

      Try hanging around here: [email protected], but understand that these SDR’s they’re using are direct down-converting/sampling types. Pre-built radios and kits can be bought here: http://fivedash.com/. The $21 “Lite” receivers are popular as pan-adapters, but you will need to supply the correct crystal or synthesized L.O. for your particular radio’s IF scheme, and different radios have different connection techniques. Ask in the Group about your particular radio. I’d be surprised if the uBITX hasn’t been done already.

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