@K5TED
The use of a connector of 50 ohms characteristic impedance to a load of 75 ohms input impedance has negligible effect on the impedance seen by the source. This is due to very small length of the connector.
Please see calculation below which show that the input impedance seen by feed coax at the input of the DVB-T dongle (through MCX connector) is 74 ohms, negligible change due to 50 ohms MCX connector.
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