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I have a problem regarding mounting of RF transceiver. The main board inside metal cabinet is floating and when I check the antenna SMA bulk connector its outer case has a connection to circuit ground. This would eventually short the chassis ground to the circuit ground via pigtail. I need advice regarding this issue.

edit: from the comments below

The frequency is 850MHz. Pout=20dBm.

enter image description here

Nick Alexeev
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Adi
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1 Answers1

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Usually the antenna ground will still be effective when connected via a (say) 1000pF capacitor. Reason: the capacitor acts like a short circuit at high enough frequency. A 1000pF capacitor at 50MHz has an impedance of 3 ohms.

I don't know what frequency you are using so the actual capacitor value depends on the application but generally this can be a way of keeping isolation from any low frequency currents that would otherwise pass through the transceiver and cause it problems. It would certainly block DC and this may be the bigger issue such as when using a positive ground supply.

On the other hand, the transceiver may work perfectly fine when grounded to the chassis.

Another option is to use an RF isolation transformer in the feed to the antenna.

Andy aka
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  • I worry ESD entring through this connection. The frequency is 850MHz / Pout=20dBm. Please have alook at the wiring here;http://s804.photobucket.com/user/tigerx5/media/question.jpg.html . – Adi Feb 27 '14 at 13:21
  • I don't see anything wrong about the wiring dude – Andy aka Feb 27 '14 at 14:43
  • Chasis ground is tied to circuit ground via rf cable at only one location... – Adi Feb 27 '14 at 15:07
  • I still don't see the problem you may be thinking of but if in doubt you can isolate at the circuit board with the capacitor idea or using an RF transformer. – Andy aka Feb 27 '14 at 15:27
  • Thanks for the help. My antenna is passive , could you please help me with some link to make isolation transformer , as I am totally new to this. – Adi Feb 27 '14 at 16:31
  • 850MHz is beyond my first hand knowledge so I suggest you google stuff. I'd do the same. – Andy aka Feb 27 '14 at 18:02
  • Difficult , many questions arise. I post a new thread for this issue... http://electronics.stackexchange.com/questions/101324/radio-antenna-isolating-transformer – Adi Feb 28 '14 at 16:47