Need a part for rf radio signal switching, not sure what to use?

Electromechanical Relays
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Good morning,

Hope you are well.

I’m currently working on my first big hardware project, but am having trouble deciding on parts. For my board, I need a switching device that will connect radio frequency antenna signals (3MHz - 30MHz) through two specific paths. When a 3.3V signal is applied to the device, it must route the input antenna signal to the first output. When a 0V signal is applied, the second output must be connected to the antenna input, meaning that the signal is now travelling in the opposite direction through the device.

I started off looking at RF switches but then was advised to look at relays. I’m not sure if either of these meets my bidirectional signal requirements though.

Please let me know what you think, any advice would be greatly appreciated.

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Hello highway417,

Welcome to the DigiKey forum.

Yes, a relay is likely the most straightforward solution for the design.

To help select a specific relay please tell us more about your project. For example:

  1. What is the power of RF signal - is this a T/R (Transmit Receive) relay?

  2. What are the anticipated environmental conditions such as lightning?

  3. What internal voltage are available - is this a 28 VDC system?

  4. Can external components be added such as a transistor to interface between the 3.3. control logic and the relay coil?

  5. PCB mount vs chassis mount.

  6. Need to coax connections e.g…, BNC, UHF, N?

  7. Shielding

There are likely more things to consider but this will get us into the ballpark.

Best Wishes,

APDahlen

P.S. Don’t forget to add an inductive kickback diode in parallel with the relay coil or the transistor switch will be destroyed.

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Hi APDahlen,

Thank you so much for the response!

Here are more specifications about my design:

  1. Signal power of the RF ranges from 1-10W, yes this is a T/R relay
  2. No environmental conditions
  3. Can only use a +5V supply to power the design
  4. Yes external components can be added
  5. This is for a PCB mount
  6. No, only using pin connections to work with other components in the radio
  7. I’m not quite sure yet. The hardware projects I’ve done before have never required shielding, so I’m not sure if this one would. How would I know if I need shielding?

In general, what I am designing is a component that will be mounted onto a PCB daughter card. This component will be in charge of changing the antenna signal path within our radio (the radio is made up of several different daughter cards each doing different things). When the signal is 3.3V the antenna will go to the receive chain (separate daughter card), and when it’s low, the transmit chain (again separate card) will be connected to the antenna.

Also, I was wondering why a relay would be more straightforward for the design?

Thank you again for the help

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4

Hello highway417,

Would something like this work for your project?

It has the 5 VDC coil which could be driven by your 3.3 VDC logic using a transistor (don’t forget the flyback diode). Similar relays included less expensive non-shielded devices may be found here. Through hole devices are also located in that link.

Kindly share your solution when your project is complete. Pictures are especially welcomed.

Sincerely,

Aaron

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