Antenna Question (2 meter and 11 meter)

You shouldn't have a problem. I had a 100' doublet for HF 4' away from a Diamond X-50 with no problems.

Worst case, you can put a high/low pass filter on whichever one is causing the problem.

 

You'll be OK...I've seen guys that will have 3 or 4 antenna's all on one tower not 5-10' apart all tuned on different frequency's.

 

Just DO NOT key the 2950 while the 2800 is on. It could blow the front end of the 2m rig. Also the A-99 you can work both 10 & 11 meters with low SWR. I get below 1:8 on 10. And below 1:5 on 11.

 

See if there's a way you can stack the new antenna so it's either directly in line above or below the 2 meter antenna. For vertically polarized antennas, physical separation provides much more isolation than horizontal separation. On commercial towers, that accounts for part of what JJD mentions about seeing many antenna on the same tower on similar frequencies -- the site manager makes sure they're mounted on the same leg or other means to keep them in the same vertical axis. Also, most responsible site managers require some fairly stringent filtering devices, like circulators and isolators, to keep all that RF from the antennas from mixing in the radios and coming out on odd frequencies or causing interference with the other radios already there.
Vertical antennas usually have a null in their pattern directly below and, sometimes above, the antenna, so putting another antenna in that direction takes advantage of the reduced signal strength.
It's not perfect. But for years before hams were able to afford duplexers that let a receiver and transmitter run (on slightly frequencies) at the same time on a repeater, they'd just run separate antennas and coaxes to the TX and RX. Frequently it could be done on the same tower by putting one antenna (usually the recieve) near the top, and the other near the bottom to get as much vertical separation as possible. When that wasn't possible, it might take using two different buildings (like a couple of guys' houses) half-a mile apart, each with half the repeater, then linking them with a separate radio band channel or phone line.
That was when the frequencies were all within the same band, like 29.xxx, or 52.xxx, or 146.xxx. You've already got some built-in isolation because of the frequency difference between 27.xxx and 146.xxx, but depending upon how you've got your Ranger "CB" ummm... tuned, you might get unwanted on-frequency energy from it coming into your Yaesu.