Re: Modifying the HF+ R3 resistor and comparing results to the Discovery SDR

Dana Myers

On 12/9/2019 3:36 AM, Kriss Kliegle wrote:
   Yes, the modification makes the Airspy HF+ nearly equivalent to the new Discovery in the area of MW and lower. Before it was completely deaf in the VLF range, after modification it actually RX's signals in the 24-60 kHz range. If your not into the VLF band, it's not necessary to modify. Signals are all digital down there anyway. If you are chasing NDB's (Non Directional Beacons, old school aircraft navigation aids), it will help RX.

   How's that?
That's exactly what I would expect - having done the "R3 bypass mod" myself
shortly after receiving the HF+. I vaguely recall using a 4.7nF cap in my case, and
it totally woke-up the VLF response - it was novel finding the VLF stations in
the ~20kHz range. I experimented a bit with an e-probe antenna but also
found, after modification, I could hear nearly as well in VLF with ordinary
HF antennas. I did not note a negative impact on MF/HF performance in my
case, though I tend to recall quite a bit of improvement from firmware
updates soon after the HF+ was released.

My curiosity was "is there something more nuanced than this in the 30-minute

Thanks -
Dana  K6JQ

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