Do you NEED an SWR meter? Unless you have a really adjustable antenna (the K40 has some adjustment, but usually you just use the factory recommended setting and they work well) or you're going to null out your cable (which you can't really do on a mobile antenna anyway) there's really not a lot of point. Just my 2¢
no antenna comes set from the factory. The mounting location of the antenna/ ground plane/length of feed wire/type of mount all play a role in the swr. So you and I could have the same truck, same antenna but I put it on the roof and you mount it on the bumper. My SWR should be close to 1:1 (but no way to know) and yours could be ok or horrible, still no way to tell without an swr meter. If your swr is 1:3 you would work ok, but your signal would be weaker and you will put stress on the transmitter. Any more than 1:3 and you will blow up the transmitter.
Oh and all antennas are adjustable. You lengthen them by cutting the cover off slightly and uncoiling, or shorten by cutting a little bit off at a time until you get the desired swr.
yes...I definately suggest buying a tuneable antenna from either your local shop or online at the site i suggested...it will work 1000x better than some cheap-o walmart or radio shack pretuned magnetic antenna or a similar product...the 40 bucks for the good antenna goes a longgggggg way! trust me.
The K-40 has a factory recommended setting, kind of a default setting if you're not going to try and tune it. They're base loaded with a center whip, there's a set screw you loosen and pull the whip up a certain amount from bottomed out. It should be in the paperwork. You're not going to truly null the cable on a mobile setup, unless you plan on coiling up a lot of coax in your trunk... maybe half or quarter, but even then.. and your sure not going to do it on a short pre-made setup like a K-40.
The K-40 is a decent little antenna for the money.
back in the day I had a cb in my car no amp just a nice unit that was all tuned and set up by a trucker. He set the swr meter antenna etc. I could talk as clear as day to anyone within 50 miles I talked with my brother in danbury ct with no problem from farmingdale. A truly tuned system means the world. Wish I still had the radio...