Simple question about Duplexer

[amirke]

I have a very simple question:

A Duplexer, which separate the RX from the TX.
It is made from band pass filters for each frequency and bandwidth.

My question is: Are those filters are working for both directions ?

For example : The Rx filter in the duplexer is generally from Antenna to board. Can I transmit RF with the same RX frequency through this filter.
/- -> LNA -> PA -\ (RX path of duplexer)
RF Signal -> Ant -> Duplexer < > Duplexer -> Ant
/- -> LNA -> PA -/ (TX path of duplexer)

Does these filters are bi-directional ?

 

[biff44]

It depends on your particular filter. If the two bandpasses are connected to a simple T junction, then they are each bidirectional. If, instead, there is a ferrite circulator joining the two filters together, then you can only use them as labeled: RX for RX only, TX for TX only.

 

[amirke]

I want to use avago ACFM-7107.
The datasheet does not says anything about the filter.
It is FBAR technology based (Film Bulk Acoustic Resonator).

What do you say about him ? Is it Bi-directional ?

Thanks

 

[Mark W. Ingalls]

Dear amirke,

The safe thing to do, since Avago doesn't have any *.snp files online for these things, is to contact Avago directly.

Go here:

If FBAR is linear and passive, then Sxy = Syx. IIRC, this is true, but you should go ahead and inquire.

 

[biff44]

Yes, that would be bidirectional on each of the 4 bands. Good luck trying to find one in stock anywhere though.

On a filter like that, I would check the power rating on each port. You might find that the filter can work in both directions, but only some of the ports can handle the 1 watt transmit power.

 

[D.A.(Tony)Stewart]

a Half Duplexer may use a Pin diode to shunt the Rx path during Tx since filters are bidirectional 2 ports.

 

[amirke]

Thanks guys.

Biff, good point.
I will check it.

---------- Post added at 11:32 ---------- Previous post was at 11:31 ----------

Biff,

How do you know that it is bidirectional ?

 

[D.A.(Tony)Stewart]

See BAW filters **broken link removed** (aka FBAR?)

 

[amirke]

Thanks SunnySkyguy,

PIN Dioode won't help me to "join" together TX and RX.

BAW is FBAR ?
tegal is a vendor ?

 

[amirke]

Avago has really poor support. They answered me 2 weeks after my question and it is not clear to me.
Here is the answer they gave me about ACFM-7107 and bidirectional issue :

" The power handling capabilities on FBAR for both Tx and Rx ports should be similar, for many customers such statement is enough and they have successful running applications.
(femtocell, one example)

But for repeaters, I saw some difficulties, in this case, deep testing is suggested. "

I don't understand this answer.

Can anyone clarify this answer ? I asked if it could be bidirectional ?

 

[amirke]

Biff,

How can you know that it is bidirectional ?
How can you know if the rated power consumption is for all channels or per channels ?