Using a single antenna - duplexing tx/rx

[gpatounas]

Hello,

I am working with OpenAirInterface and need to connect the BladeRF to a Huawei E392u-12 modem on LTE band 7, using a single RF cable (since the modem has a single antenna).
Later I will need to use a single antenna for tx/rx primarily in LTE band 7 (2500-2570 UL, 2620-2690 DL) and if possible (ideally using the same hardware), 2.4GHz band and possibly 5.8Ghz.

Is there no possibility to switch BladeRF to using a single antenna programmatically?
If not, what hardware should be used to duplex tx and rx together?
From what I understand a diplexer is not sufficient to multiplex the UL and DL channels of LTE band 7.
I have found some circulators and duplexers that should work but could be expensive or are surface mounted components.

In conclusion, as far as I can tell I need a duplexer/circulator with sma connectors but would like to know what is the standard hardware for this use and if there are any specific proposals.


Regards

George

[bpadalino]

So I am not a wireless telecom expert, but here are my answers to the best of my ability.

For 5.8GHz, you won't be able to use the bladeRF without adding some type of frequency translation to an IF that the LMS6 can understand.

LTE is typically FDD though there is a TDD implementation specified as well, so you'll probably want a duplexer like the Avago ACMD-6007 or similar.

I am curious about your statement regarding the duplexer not being sufficient enough for UL/DL separation? If you wanted to add more filtering on the RX side, you could use an extra BAW/SAW filter?

As for the best way to tackle this, I'd say you can spin an expansion board to sit on top of the bladeRF, or you can make a board that has 2 SMA's on one side, and 1 on the other - with the 2 SMA's separated by the distance on the bladeRF RX/TX ports.

Sorry I couldn't be super helpful, but let me know if you have questions regarding what I have said here.

[gpatounas]

Thank you,

I was referring to a diplexer (a form of duplexer) which basically consists of 2 filters to multiplex two frequency bands.

[gpatounas]

I am still unclear on this subject.
It seems to me that this should be quite a common requirement in the SDR community but there don't seem to be any straightforward answers, although this could be entirely my fault.
I have contacted several manufacturers for an LTE band 7 duplexer but the offers I get are of a very high price and more suitable for high-power applications.

The specifications I have determined (based purely on what is available) are:
Insertion loss <= 1 dB
Band ripple <= 0.7 dB
Isolation >= 75dB
Impedance = 50 Ohm
Power rating 1-10 W

My questions are:
Do I need a duplexer, a circulator, a diplexer or something different?
Is there some specific hardware or manufacturer that you can suggest?
Are there specifications that I need to be aware of?


Thank you,

George

[dave]

Maybe you'd turn up some relevant discussion in the OpenBTS community because -- even with separate antennas and even with 2G (GSM) -- the downlink signal makes it difficult to get a good SNR on the uplink.