RF Switches - Page 1
Forum section: electronics / projects

author: yanir
author_rank: Regular Contributor
timestamp: August 29, 2014, 06:43:33 pm
content: Hi, for the RF gurus out there:I'd like to share a single 2.4Ghz antenna between two RF transceiver IC's (Wifi, and BLE). I only need one operating at a time and can handle graceful handover in software.My question is:Can I use an RF switch like this to switch the antenna path from one to the other?:http://www.mouser.com/ds/2/249/MASWSS0115-318361.pdfI assume this part is bidirectional and would work, but after reading the datasheet I wasn't totally sure. If this is not the correct part, any recommendations would be greatly appreciated. Also, if you think this is a terrible idea, please tell me. I'm not an RF engineer, but I have done successful layouts for RF IC's including basic (app note guided) antenna layout.Thanks!Yanir

author: German_EE
author_rank: Super Contributor
timestamp: August 29, 2014, 07:34:24 pm
content: If you look at the datasheet you will see that they do not specify which are the input and which are the output ports, the switch is bidirectional. It will probably work in your application but at these frequencies you will need to be very careful when it comes to matching and use 50 ohm lumped lines everywhere.Disclaimer: My RF expertise stops at about 500 MHz, I am therefore far outside my comfort zone here.

author: yanir
author_rank: Regular Contributor
timestamp: August 29, 2014, 07:50:39 pm
content: Thanks German_EE,The datasheet labels them asRF Port 1 - I'd use for WifiRF Port 2 - I'd use for BLERF Input - I'd use for the AntennaDoesn't RF Input imply input only? I want to be wrong, and hopefully it's just poorly labeled.

author: jlmoon
author_rank: Unknown
timestamp: August 29, 2014, 07:56:35 pm
content: How about one of these?http://www.minicircuits.com/pdfs/VSW2-33-10W+.pdfor even this one if you don't need the power characteristicshttp://www.minicircuits.com/pdfs/VSWA2-63DR+.pdfThey make some great stuff.You will need to match the part to your interfaces through the associated matching networks

author: krenzo
author_rank: Regular Contributor
timestamp: August 29, 2014, 08:30:50 pm
content: I've worked with several RF switches, and I've never heard of one that is unidirectional.

author: yanir
author_rank: Regular Contributor
timestamp: August 29, 2014, 08:35:55 pm
content: Quote from: krenzo on August 29, 2014, 08:30:50 pmIt makes sense, but since I've never used one before I am proceeding with caution. I did find a vendors brochure that stated their switches are generally bidirectional implying they sell some that aren't.Quote from: jlmoon on August 29, 2014, 07:56:35 pmThanks, I'll take a look. The first one is definitely beefy. More than I need for this.

author: yanir
author_rank: Regular Contributor
timestamp: August 29, 2014, 09:10:39 pm
content: Another question regarding specs.Reflective VS Absorptive? After doing some reading I think I understand that If the switch is open it can either be a reflective or absorptive (with a 50ohm load). So when I have BLE 'off' and disconnected, if it attempted to transmit, it could either get a full reflection or be absorbed. Am I correct?Continuing this thought, I need to check the data sheet for the part and see what kind of power it could handle being reflected back on the RF line. If it's absorptive, I don't care.Also, since I can control in software whether or not they are transmitting during the off state I should be able to avoid any problems, but bugs happen...