2-Way RF Switch

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The 2-way RF switch is a new addition to the Portsdown system. It decodes a signal sent on the symbol rate switching lines (all 3 high, which was previously unused) which is used to indicate that the LimeSDR output should be used, rather than the Filter-modulator board.

2 Way Switch.jpg

The block diagram shows a comprehensive arrangement with all the features. Many of the blocks are optional – it depends on your requirements.

Output Switching.JPG

Schematic

2 Way switch Circuit.jpg

Test results

The test results for the switch (when running from 3.3v) were:

Frequency Insertion Loss Isolation
71 MHz < 0.5 dB 36 dB
146 MHz < 0.5 dB 35dB
437 MHz 0.8dB 35dB
1255 MHz 1.5dB 21dB
2405 MHz 3.5dB 19dB


The insertion loss at 2405 MHz can be reduced by 0.5 dB by trimming the centre pins of the SMA connectors to be flush with the underside of the PCB. A further improvement could probably be made by trimming the RF tracks on the top of the PCB so that they do not extend beyond the SMA centre pin.

The PCB for the RF switch is available from the BATC shop and construction details are posted on the BATC Wiki.