Antenna Switching

[NJ Roadmap]

Ok so I'm using a 433MHz quarter-wave antenna for a TX and RX module and I need to switch the antenna between the TX and the RX module since both shouldn't be connected to the antenna at the same time. I understand that PIN-diode switching is reliable and has been done for years. But I'm no RF pro so I'm going to need some help!

Here's the good info I've found, all I need is to know how to interpret the variables in the equations given (all the info is on Pg.1 and Pg.2):

https://www.avagotech.com/assets/downloadDocument.do?id=1624

I want to replace the lambda/4 transmission line shown on Pg.1 with the equivalent circuit shown on Pg.2, but I'm not sure what Zo is!

Also has anyone done PIN-diode-based switching in the past?

p.s. As much as it would make it a lot easier, I don't want to use the IC mentioned at the bottom of Pg.2 for many reasons, the main one being cost.

 

[Leftyretro]

Ok so I'm using a 433MHz quarter-wave antenna for a TX and RX module and I need to switch the antenna between the TX and the RX module since both shouldn't be connected to the antenna at the same time. I understand that PIN-diode switching is reliable and has been done for years. But I'm no RF pro so I'm going to need some help!

Here's the good info I've found, all I need is to know how to interpret the variables in the equations given (all the info is on Pg.1 and Pg.2):

https://www.avagotech.com/assets/downloadDocument.do?id=1624

I want to replace the lambda/4 transmission line shown on Pg.1 with the equivalent circuit shown on Pg.2, but I'm not sure what Zo is!

Also has anyone done PIN-diode-based switching in the past?

p.s. As much as it would make it a lot easier, I don't want to use the IC mentioned at the bottom of Pg.2 for many reasons, the main one being cost.

You didn't state the power level of the transmitter but if it's only milliwatts Ithink the simplest device to consider is either a SPDT reed relay or 2 SPST relays switching in opposition.

Lefty

 

[JimB]

I made an attempt at a UHF PIN diode switch some years ago, it was not a success for what I wanted, probably because I was using "whatever was available", which was probably not suitable for the job.

If you use new branded PIN diodes, you should have no problem.

For the lambda/4 line, I would try a length of coax cable, (dont forget to allow for the velocity factor of the cable when deciding the length).
If you want to use the discrete component solution, make Z0 = 50 ohm.

OK about the IC, then just use discrete PIN diodes, at the moment I dont have any obvious suggestions, but there is a reasonable selection of PIN diodes in the RS catalogue, but beware of the minimum order value etc.

JimB

 

[Hero999]

You can buy special RF relays; look in RS or Farnell.