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900Mhz Antenna Solution Study

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#1
Hi. This is my first time to create a forum and in need of help. Basically I have an SDR type Cellular base station with two separate radio channels with 3Watts each. I have two options a) use panel antenna for each or b) use an omni antenna but will naturally need a combiner.

My concern is if I opted to do option b, will it be safe enough to straight forward connect my radios to combiner towards the omni antenna or will I be needing a multi coupler and then the hybrid combiner before it goes to the omni antenna?

Freq I'm working at is 890-960Mz but the tx and rx spacing of each of the two radios is still undefined as I still am clearing those up with the radio supplier.

Appreciate any help.

/AREF
 
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#2
If you want to combine two separate transmitters that are close spaced in frequency you would need a 3dB hybrid with isolator type combiner that will loose at least half your transmit power in the combining process. If you are combining two different cell phone bands like 800/1900MHz you can use a filter type combiner with less loss.

You will also need a multicoupler for the receivers to combine them onto one feedline and that is usually a preamplifier and power divider to feed each receiver. If you want to use a single antenna for both transmit and receive you need a duplexer to isolate the transmitters and receivers and one side of the duplexer would connect to the output of the transmitter combiner and the other side of the duplexer would feed the input to the receive multicoupler. Then a single omni antenna would work for the entire system.
prcguy

Hi. This is my first time to create a forum and in need of help. Basically I have an SDR type Cellular base station with two separate radio channels with 3Watts each. I have two options a) use panel antenna for each or b) use an omni antenna but will naturally need a combiner.

My concern is if I opted to do option b, will it be safe enough to straight forward connect my radios to combiner towards the omni antenna or will I be needing a multi coupler and then the hybrid combiner before it goes to the omni antenna?

Freq I'm working at is 890-960Mz but the tx and rx spacing of each of the two radios is still undefined as I still am clearing those up with the radio supplier.

Appreciate any help.

/AREF
 
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#3
Thanks very much prcguy.

I may have to settle for a separate antenna for now just to spare my precious transmit power.
 
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#4
Just wondering...Output of my SDRadio is a single Tx/Rx port for each channel. Obviously combining and coupling has already been done inside. If in case I want to combine these two channels, is it still possible to combine into single omni antenna?

Rgrds
AREF
 
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#5
Anything is possible with enough money. Since the combiners are going to introduce a not insignificant amount of loss, you'd probably be much better off using 2 separate antennas connected to the 2 separate receivers. Unless you have a really long coax run, it'll be cheaper and easier in the long run.
 

AREF

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#7
High gain Antenna for a low output power SDR

Hi again....

Im wondering if my new SDR with output power of 100-200mw can drive an 11dbi omni antenna or am I stuck with a 0-3dbi gain antenna?
 
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#8
Hi again....

Im wondering if my new SDR with output power of 100-200mw can drive an 11dbi omni antenna or am I stuck with a 0-3dbi gain antenna?
Yes, it'll drive it. The dB gain of the antenna doesn't limit what you can drive it with.

There are limits for power into an antenna, but it's more about what is safe and what the conductive elements inside are capable of handling.

What you would need to be concerned about is the legal side of this. Some radio service allow a maximum transmitter power level, others have a maximum Effective Radiated Power. Using too much antenna gain can raise the ERP above what is legal.

Not knowing where you are or what radio service you are trying to work under would make that impossible to answer.
 
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#10
Ettus B210

I’ve been working on an OpenBts SDR platform https://www.ettus.com/product/details/UB210-KIT and trying to decide what antenna and how I should best configure it with greater coverage radius in mind. The radio can give a max output of 100mW. I know I need to amplify each channel and duplex as a single antenna but not sure how much, if there is any, coverage will improve. Will any PA output power do e.g. 10W, 15W etc? Will the PA be driven by this small amount of power from the radio?

Anyone had the chance to work on this platform or recommendation is greatly appreciated.
 
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#11
So, for the antenna, you'll want an omni-directional vertical with as much gain as you can get. That will increase the Effective Radiated Power by flatting out the radiation pattern so most of the energy is in the horizontal plane.
That works well, however it can work against you if the receiver is somewhere other than close to the horizon.


I really think you need to stick with separate outputs. Combining the two outputs together can work, but it's going to cost you:
-The combiner will eat up some of the RF power. Losing half your power through a combiner is pretty common.
-Your TX frequencies will need to be separated by a certain amount and you'll need to keep the frequency fixed.


As for RF power amplifiers, this shouldn't be a problem. Here in the USA there are commercial radio services in the 900MHz band. There are repeaters that only put out a few hundred milliwatts and are used to drive larger amplifiers.
While not the same frequencies, I have 800MHz repeaters that put out about 300 milliwatts and drive RF amplifiers that increase that to 80 watts.



I've never used one of those radios, but it sure looks interesting.
 
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#13
To follow on that mmckenna...will a separate panel antenna Vertical work or I will be on the same risk as the Omni Vertical? Or should I use x-pol antenna then?


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#15
I mean if I use a separate directional antenna Vertical instead of combining into an Omni antenna Vertical, am I essentially on the same risk? Will it be helpful if I use cross polarized directional antenna?


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#16
You might be able to use a two port antenna that was set up for cross polarization. Most cellular base station antennas are set up like this:
Port 1 = -45º
Port 2 = +45º

Either way, you will need to keep the two antenna connection separate. Even with separate antennas you need to have enough isolation between the two. With one radio/antenna transmitting, it needs to have enough isolation from the receiving antenna to keep the transmitted energy from getting into the receiver and overloading it.

Physical space between the two antennas is one way of doing it. Filtering is an option if your frequencies are fixed and have enough separation.
 
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