Help please, with purchasing a cb

See if you can find a Uniden PC78 Elite. Basically a tricked out cobra 29, but Unidens have historically been a tad better than comparable Cobras. You can get them new in box still on eBay.

What antenna to get depends on what you're going to be mounting it on.

 

I ran the "Terminator II" dual-coil antenna that PFJ/Love's sells on my '10 Prostar with quite good results.

Also,get a good aftermarket mic. My favorites are the Ranger SRA-198 for a noise-canceller, or the RF Limited CR-577 for a power mic. Bob's CB shop has both in stock on the shelf, in Strattanville, PA, I-80 exit 70, if you make ever make it through there.

 

You will need to tune the antenna for best results.

 

No such thing as an antenna that's ready to go, unless you just get lucky. You almost always have to do some tuning. You could run a 4-1/2' Francis fiberglass antenna, they are usually close enough that you can generally throw them up and use them, but my most recent one needed 1/2" cut off the top of it to be just right.

Also, for educational purposes: some radios have built-in SWR meters. Most of these have a calibration mode/knob. THIS DOES NOT TUNE THE ANTENNA, as too many people seem to think. It only sets the meter, so you get an accurate reading. The only way to tune the antenna is to shorten or lengthen it. Period. Also: SWR higher on channel 1 than channel 40 indicates an antenna that is too short, SWR higher on channel 40 than channel 1 indicates an antenna that is too long.

 

If you are asking if you need to have a "peak and tune" done to the cb itself, no, you do not.
You should tune the antenna on the truck for lowest swr, like volvo244 suggested. Some cb shops will tune your antenna for you.