Model 600 wireless-N signal fluctuates

Question

Dear Folks,
            I work for a grading contractor here in North Carolina and my job is to get their offices hooked up to the internet.  Unfortunately, I’m having a strange situation with the wireless network I am trying to hook up.  The facility at which I work has three physical buildings.  I’ll call them A, B and C.  Building A is wired for internet access so I bought the Linksys 600 wireless-N router which I hook directly to my cable modem.  All the PCs that are wireless in building A work great.  They all have the WUSB300N wireless antennas. 
Building B is about 75 feet from building A.  In that building, we have one PC with the WUSB300N antenna.  The antenna in Building B is in the window and directly faces the model 600 router in building A.  It is in a direct line of site.  You can look out the building B window and clearly see the 600 router.
Building C is about 125 feet from building A and there is one PC in that building and it has a WUSB300N antenna.  The antenna in Building C is up on the second floor in front of an open gable vent.  You can see the model 600 router in building A from the gable vent so it too is in a direct line of sight, just further away.  And now for the situation.
As I mentioned, the PCs in building A have no communication problems.  They work great.  The PCs in Buildings B and C get intermittent reception.  They start out with a GOOD reception and then it goes down to LOW and then VERY LOW and then it is gone.  A few minutes later, it comes back to GOOD.  This happens all day long.  At first, I thought that there could be something wrong with the 600 router in building A but what is really strange is there are two other Linksys wireless routers in the neighborhood that I “see” (both are G’s) and when our model 600 signal disappears, so do all the other signals from the neighbors’ routers.  It seems as though our building could be in an RF dead area or there is something killing the air in which these signals travel.  Has any one ever seen a problem like this before?  Thank you for your time!  Chris

Answer 1

The WUSB300N is a 2.4 GHz only device, so any microwave, cordless phone, etc can degrade your reception (just as with the wireless G/B devices).
A WUSB600N is a dual band just like your WRT600N, and there is less noise on the 5 GHz frequencies.  Also on the WRT600N, you can safely set the 5 GHz band to wireless-N only and keep the 2.4 GHz band as mixed mode (to cover wireless b/g and 2.4 GHz only n).  Just keep in mind at 5 GHz any solid object (including your hand), in front of the antenna can degrade the speed.
Changing channels might work, reducing external noise on 2.4 GHz will be the best bet if it not a channel conflict (move the microwaves and other devices, or notice if they are being used when it degrades).