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by anonymous
Hi to all, I need to work in a remote location, far from 4G repeaters.
I can see two different repeaters working on two bands:
- 800 MHz
- 1800 and 2100 MHz

I have no available wide band-high gain antenna to cover 800 to 2100 MHZ so I need to use two different high gain, directive, 4G antennas.

How should I connect these two antennas?
I supposed something similar to:
- main antenna = 1800-2100 MHz
- aux antenna = 800 Mhz
Is this right or should I do something different?
Thanks.
by anonymous
As I understand it;

If your unit has one internal radio (essentiall, anything other than the RUTX14 which has 2x internal radios)

Then the two antenna ports operate in this way:

The "main" antenna port is the primary TX/RX antenna for that single radio.

The "aux" antenna port is used as a "diversity" antenna for the main antenna.

This does a few things:

It enables 2x2 MIMO (both antennas used at the same time for DL -LTE Cat4)

It allows your radio to take better advantage of a concept called "signal diversity".
-essentially, it allows the radio to use both antennas at the same time for the SAME SIGNAL; ideally for LTE cell towers, you would have the two antennas in a "cross polarization" orientation. I.E. one antenna rotated 90 degrees relative to the other.

In order for these advantages to work to their maximal effect, BOTH antennas must be matched, I.E. exactly the same.

And, in any case, even if you use mis-matched antenna types, the SINGLE radio in your device can only connect to ONE band at a time (unless your unit support Carrier Aggregation -LTE Cat6 or higher- more on that below).

So, the radio will either connect to a low band frequency (I.E. ~800Mhz) or a mid band frequency (I.E. 1.8-2.1 Ghz).

It will NOT connect to one band on one antenna port, and a different band on the other antenna port.

Carrier Aggregation:

In Cat 6 and higher modems, "Carrier Aggregation" comes into effect if:

-Your device support it;
-your device will have SPECIFIC band combinations that it supports, you will have to look them up for your specific unit

-The tower you are pointed at supports it;
-the carrier equipment on the tower you are pointing two is emitting signals on multiple bands simultaniously AND that carrier has "turned on" the carrier aggregation feature on that particular tower

-And the bands that are POTENTIALLY being aggregated on the tower you are actually pointed to match the band combinations supported by your unit
-I.E. the tower supports CA on band 2+66, 12+66 and n41+66.
-You device only support CA on band 2+12 and 2+17
-In that case, even though your device technically support CA, and the tower you are pointing supports CA, you still wont see the advantage of it, because the band combinations supported by your device do not match the band combinations emitted by your tower.

Okay, so in the miraculous case that your unit supports CA on band combinations that are emitted by the tower you are pointed at, again as I undertand things (I could be wrong):

The band combination is done over each antenna channel;

So antenna channel 1 (main antenna port) would be seeing Band 2 + 12 (for example)

And antenna channel 2 (aux antenna port) would also be seeing Band 2 +12 (for example)

SO, for maximum signal integrity, you would want a matched pair of antennas that had wide enough bandwidth to cover the band combinations you intended to connect to.

All of that said; in your case:

I would recommend you test both antenna's independantly on the MAIN antenna port.

Determine through load testing/ speedtest's which Band has better service on the tower(s) you can connect to.

Once you have determined which Band is best for your location and the tower(s) you have available:

Lock the unit to only connect to that "preffered" band.

Connect the antenna matched to that band to the "main" antenna port.

Connect the stock omi-directional "stick" style antenna that came with the unit to the "aux" antenna port.

Tune the main antennas location and pointing direction.

LTE signal can be deceptive, especially at long range/ Non Line-Of-Sight.

It is often the case that obtaining the maximum signal STRENGTH does not actually result in the best data rates.

The reason?

NOISE.

For this reason it is also often the case that "just" placing the antenna as high as you can may not yield the best data rates.

You will need to experiment in your location with your antenna(s).

Things to consider:

The MOST IMPORTANT METRICS for you to looks at are in this order:

SINR:
-If you can't get this above +0 DBi then forget about every other measurement, your signal will be CRAP.
-If you can get this above +20 DBi AND your RSRP is -100 DBi or better, you will be able to achieve maximum data rates (the limit will be your units LTE modem, and the throughput available at the tower -congestion/backhaul etc.)

RSRQ:
-this is similar to SINR but doesnt include "general RF noise"
-this measures "noise" relative to signal stregth, but the only "noise" included in this measure are the OTHER cell towers you can also hear on the band you are currently connected to
-at -10 DBi or better (providing SINR is also +20 or better) you will be able to achie maximum data rates

RSRP:
-this is the stregth of the signal you are receiving from the tower you are currently connected too
-if SINR is +20 or better AND RSRQ is -10 or better, then once your get to -100 DBi RSRP you will be able to achieve maximum data rates
-that is to say, if SINR and RSRQ are at "excellent" levels then you will see NO BENEFIT from getting your RSRP better than -100

RSSI:
-for 4g LTE signals this measurement is almost ENTIRELY USELESS
-it is TOTAL WIDEBAND POWER
-it is the strength of ALL available signal added to the strength of ALL audible noise
-so, if you turn your antenna looking for MAX RSSI, you are probably going to find the area with the highest noise floor, and thus one of the worst directions for receiving a good signal

So, for tuning your antenna placement:

Try various location around your building/ structure;

You may find that placing the antenna on one side of the building such that the building itself blocks "noise" comming from a certain direction, you can obtain a better Signal to Noise Ratio (SINR) and thus better data rates, even if you sacrifice some TOTAL power of signal strength (I.E. SINR goes up, but RSRP and RSSI go down -that is actually a good thing)

Good luck in your RF journey!

1 Answer

0 votes
by anonymous
Ok, thanks... I'll do further tests.
I don't need high speed but I need link will be always present. Worst case would be link up and down continously.
I must take care of all bands and I have no available wideband antenna, once installed I can't access to the site so I think I'll need to connect both antennas to same main port.
I remember there was a "multiplexer" to do this on 2.4GHz, I hope to find something similar..
by anonymous

"I remember there was a "multiplexer" to do this on 2.4GHz, I hope to find something similar.."

I do not have any experience doing this myself yet, but I believe you are absolutely correct;

If you want to connect two different antennas to the same antenna port (usually done to increase the frequency range as you are attempting to do) then the two antennas must be connected together through what is known as a "diplexer" / "duplexer" / "multiplexer".

As you are combining two antennas I am pretty sure you are looking for a diplexer -dont quote me on the exact name, but this is definitely the type of thing you are looking for;

One big thing to consider on the diplexer/multiplexer you select:

 

"Insertion Loss"
-essentially, how man db's are lost through the diplexer; a "good" multiplexer should have "low" insertion loss.
-IMHO I wouldnt get anything with an insertion loss over 2 db's, and I would prefer if it was under 1 db of insertion loss.

Next thing to consider for the diplexer:

Do they have an effective frequency range?
-I dont know the answer to this one, but I assume you are going to want to find a diplexer/multiplexer that work efficiently within the frequency range you intend to use it. 

I.E. 800 - 2100 Mhz 


For reference sake;

Poynting antennas has YouTube video where they take the case off of their various antenna designs and demonstrate/ present the various design elements within the antenna, being careful not to reveal information that they have not yet patented. 

In these videos they clearly state that they use a "very low loss" diplexer to combine low band antenna elements with a mid-band antenna elements in order to create antennas with very wide effective frequency ranges.

So, provided you get a "good" diplexer/multiplexer, this should work EXACTLY as you envision;

I would still recommend occupying the "aux" antenna port with one of the stock Teltonika stick antennas that came with the unit; it will absolutely help.

by anonymous

"I don't need high speed but I need link will be always present."

All of those signal strength references I detailed in the context of "data rates", BUT:

Link stability is ABSOLUTELY related to the same number.

If you cant get your SINR (Signal to Noise Ratio) above positive 0 dbi you will NEVER have a stable connection, period.

If you can get your SINR to average +10 dbi and NEVER dip below +5 dbi, you can reasonably guarantee your link will never go down.


SOMETHING TO CONSIDER

If you are setting everything up on a beautiful spring day with clear skies from horizon to horizon then average +10 SINR with no drops below +5 wil llikely NOT be good enough to guarantee a stable link.

Why?

-Bad weather! 

As I undertand it, from the research, you should basically "bet" on a 5-10 dbi reduction in signal numbers if you happen to have a heavy rainstorm between you and the tower.

Thick fog can get almost as bad as that.

SO, if you want to guarantee year-round link stability, you NEED at least a 5-10 dbi buffer when measured on a perfect clear day to account for the loss you will see during incliment weather.

SO, for a link that needs to be 100% stable year round, you really cant afford to dip below +15 SINR on a perfect clear day.

As far as RSRP is concerned, as long as you maintain the above SINR numbers, you need ~ -90dbi of RSRP on a perfect clear day to keep you from dipping below -100dbi on a bad weather day.

Good luck!