External Antenna for Clear 4G Mobile USB

[thuor]

This is the Ubee Interactive PXU1900 USB modem.

Yes this does have an external antenna port - Finally!!! Hint hint - anything that has a docking cradle to provide a higher gain would normally have an external antenna port that interfaces the USB modem to the higher gain antennas in the docking cradle.

We have the antenna adapter for this on order and should have it in stock before 4/9/2010. We also have different styles of indoor/outdoor WiMax antennas in stock and ready to ship. Note that while 2.4Ghz antennas could work if they were designed wideband these are not recommended unless the spec's clearly shows their performance at the 2.5-2.7Ghz band. Parameters such as Gain and VSWR typically roll off when you go above the tuned frequency.

Check out the PXU1900 table for links to external antenna adapter, low loss cables and wimax antennas.






WiMax Antennas

Check out E-Store for some pre-configured kits

LMR-400 Low Loss Coaxial Cable

Check out E-Store for cheaper but more lossy cables

[thuor]

PXU1900 antenna adapter

Here is a link to the PXU1900 antenna pigtail



The Clear 4G USB Modem (PXU1900) has two antenna ports for RX Diversity. There are cases where you could get away with using only one external antenna. This boils down to when MIMO diversity is most needed. For an outdoor elevated antenna with line-of-sight or near-line-of-sight to wimax tower, MIMO plays a less important role than for cases where multipath propagation is prevalent (uncorrelated paths). Also in many cases when your outdoor signal is already very strong you may not need a second antenna.

The USB modem external antenna port has a switch that is normally closed (NC) and is open when you mate it to this antenna pigtail. This means that when you attach only one external antenna you still have the 2nd internal antenna active for diversity.

When you attach only one external antenna be sure to place it on "ANT1" (see pic in previous post above). I.e looking at the back of the USB modem with the USB interface to the left, "ANT1" is the bottom port.

[scottpet1973]

Two antenna question

I have the Clear 4G USB modem (PXU1900). So, optimally, I would need to buy 2 separate antennas (as in two indoor panels, for example), and two sets of cables?

I'm looking to purchase a set up for my house and a separate set up for my car.

What advantage will having both antenna ports used with cables and antennas provide? Will it be more beneficial for the house set up or the car set up. Or, does this even matter?

Thanks for the great dicussions/information.

Scott

[thuor]

I have the Clear 4G USB modem (PXU1900). So, optimally, I would need to buy 2 separate antennas (as in two indoor panels, for example), and two sets of cables?

Exactly! And the key word is "Ideally". The two antennas help with MIMO spatial diversity & coding gain which translates into better speed and better coverage. There are instances where a signal antenna will perform just as well as dual antennas and the need for a 2nd external antenna would not be too big. This includes:

• if you can elevate and orient the directional antenna to give you a clear RF line-of-sight to a wimax tower or to a very strong dominant signal. Notice i say "RF" line-of-sight (LOS) which is quite different from an "optical" line-of-sight. RF LOS takes into account Fresnel Zone clearance so even if you can "see" the wimax tower from antenna location you should not be grazing over trees or buildings.
• most MIMO implementations are on the downlink channel (forward channel) only so if your primary use of this is for uplink (e.g uploading video to a remote server) then dual antennas are not that important to you.

I'm looking to purchase a set up for my house and a separate set up for my car.

What advantage will having both antenna ports used with cables and antennas provide? Will it be more beneficial for the house set up or the car set up. Or, does this even matter?

It will be more beneficial for the car for the reasons above (can't typically get LOS in a car) and also because the mobile antennas have quite low gain about 3dBi. In the car the main goal is to overcome the RF shielding effect of the vehicles body and NOT really to boost the WiMax signal since you really cant do this with a 3dBi antenna (in fact the docking station has more gain!).

Here is an example setup for use in the house where you use a 16dBi directional antenna as the primary antenna and a 12dBi omnidirectional antenna as secondary: http://www.rfwel.com/support/tech-dr...l_Antennas.pdf.

The idea in the drawing above is that the primary directional antenna is oriented to the strongest signal and the secondary omnidirectional antenna is placed as far as practical from the primary antenna. MIMO works best when the path from the transmitter (WiMax tower) to the receiver (wimax modem) are as uncorrelated as possible which is why this setup works best as described. Having an omnidirectional secondary also helps if the primary path goes down since you can pick up from another direction.

Finally, realizing it's extremely difficult to predict RF propagation for a general user without a site analysis, the best approach is usually trial-and-error. You start with a single directional antenna oriented as best as you can and if your performance is already maxed out then you need not add a secondary antenna. If not there are some experiments we can recommend to determine if a 2nd antenna would help given what your before and after RSS/CINR readings are vs if your RSS is just too low to be boosted by any passive antenna.