I don't understand the math behind this. The 50 ohm input Z of the K3
terminates the transmission line. The SDR sees whatever voltage is
across the K3 input. More to the point, why does it matter? In most
real world stations, especially below VHF, noise from the antenna is
sufficiently greater than circuit noise that circuit noise doesn't
matter. A ratio of 13 dB satisfies this condition.
73, Jim K9YC
On 4/8/2019 2:15 PM, Joe Subich, W4TV wrote:
However, since the K3 receiver is relatively close to 50 Ohms, it
*WILL* load the input of SDRs with high input impedance - to the
extent that the SDR *can* lose 10 dB or more of sensitivity.
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