Hardware: Missing DC blockers for RF Switch PE4259

softerhardware / Hermes-Lite2

A second generation low-cost amateur HF software defined radio transceiver.

http://www.hermeslite.com

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Hardware: Missing DC blockers for RF Switch PE4259 #110

Closed rfrht closed 5 years ago

rfrht commented 5 years ago

Hi there, congratulations for the project!

After reviewing the schematics, I have found that U10 and U11 (PE4259 RF switches) has no DC blockers.

As per PE4529 datasheet, verbatim: "All RF pins must be DC blocked with an external series capacitor or held at 0 VDC."

Might be related to Issue #46.

Just a heads up and hope that helps!

73s de PY2RAF.

softerhardware commented 5 years ago

Hi,

Thanks for the feedback. The output of the opamp is DC biased, but there is a blocking capacitor between the opamp and the PE4259. The other connections to the PE4259 are not DC biased (at 0VDC) so do not need a blocking capacitor. There have been no issues here now in almost 200 units. We followed this application note: https://www.psemi.com/pdf/app_notes/an27.pdf

73,

Steve kf7o