Update: "Antenna detection" on the B593s-601
After doing some more experimentation on this issue, I made this short video which demonstrates how the antenna detection seems to operate on the B593s-601.
This follows on from the previous measurements
here and the discussion that followed.
[video=youtube;uW4fz-vS_E8]https://www.youtube.com/watch?v=uW4fz-vS_E8&feature=youtu.be[/video]
Practically, the video shows that when the B593s-601 is configured for automatic antenna detection, connecting any device with a DC resistance of around 1.2kΩ or below will cause the B593 to "see" it as an external antenna and try to use it for signal reception. The flat whip antennas that ship with the B593s-601 have 1.2kΩ DC resistance, so they will be detected and used, as will any antenna that has zero DC resistance (a "DC short").
As before, note that the auto-detection on the B593u-12/u-91 may work slightly differently. From
Conrads's measurements, we already know that the DC bias voltage used on the B593-u91's SMA sockets is higher.
Also bear in mind that the B593 may or may not apply other criteria before finally deciding to utilise the external device.
On a more technical note, the following :
1) The bias networks for the two SMA ports are somewhat linked, so placing a load (ie a low resistance, or short-circuit) on one, will reduce the voltage measured on the other.
2) The internal circuitry that provides the DC bias voltage on the B593s-601's antenna ports produces about 1.8VDC (open-circuit voltage) and has a source resistance of around 25kΩ. This means that the current that flows when the antenna port is short-circuited is only some 70μA. Practically, this means that connecting anything with a comparable resistance (ie 25kΩ or less) will reduce the measured bias voltage by half or more. Connecting a 1.2kΩ resistor will collapse the voltage almost completely (to around 70mV).
