Cobra 29 LX, not receiving weather channels

Some antenna's are better than others at picking up the weather channels...I would think the K 30 would pick them up tho...I know the Wilson 1000 and 5000 will........

The K 30 is a (for lack of a better term) a cheaper built antenna....could just be too short to pick up the weather channels unless your real close to the transmitting station...

 

Your K30 has a coil/capacitor matching network in the base which is severely blocking VHF frequencies. Nothing will cure this you will have to go with another antenna design, preferably a whip which will pass above 160 MHZ as well as 27 MHZ.

 

Yup, what Outlaw said. Being able to receive VHF on the kinda wimpy front end built in to WX-band CBs really counts on the fact that most weather transmitters run between 300 and 1000 watts so they can saturate their coverage areas. That'll make up for a lot of really inefficient antennas, like the teensy stubbies on handhelds that are the size of FRS radios, etc.
As Outlaw said, any time you shorten an antenna for convenience, the matching makes the frequency range it'll cover much sharper, as well as lower gain on its design freq range. There are dualband (30-50 and 150-175) antennas, or you can price a separate 18" whip and feedline and a diplexer to run both feedlines into, then one coax to your radio.
The diplexer route might cost a little more, but will allow you to use a more efficient CB antenna when you have the space without dinking with your weather reception. (Note that "dinking" is a technical term.....)
Hope I didn't gild the lily; as usual, Outlaw's answer was great
73,
Handlebar

 

If you try to run two antenna's to that radio the way your thinking...."K40 for the CB, and something else for the Weather band" your asking for more problems than you can shake a stick at...

Antenna's I know will work with that radio to pick up the weather channels, I know the Wilson 1000 and 5000 will work, so will the 102" whip, Predator 10K, FatBoy R-4, Any of the Mr. Coily antenna's, Monkey Mades, Tram's 10K knock-off, and some of the FiberGlass antenna's you can find in local truck stops...if you go "Fiberglass" if they will work with weather bands, they usually say-so on the package...If you do't see it, look at something else.

 

If you're not familiar with a term I use (like "diplexer" as used above") it might be worth it to the OP to be able to investigate it, rather than have someone who's clearly *not* familiar with it, i.e.,
"your asking for more problems than you can shake a stick at..."
lead him astray with generalities. The only problem one could shake a stick at with a diplexer that's made for the correct band combination is the same as any antenna: bad jumpers/connectors/mounts.
I've done this for a living, with a commercial license, for 38 years; a CBer for 45; and a ham for 50. Suppose that's enough to have worked this stuff out?

73,
Handlebar

 

RC -- eekBay is full of inexpensive stainless steel VHF whips with mounts and decent coax and connectors for under $20. My personal preference after years of using them for ham and public safety stuff has been for ones that use what's called an NMO base fitting. It goes in from the top through a 3/4" hole, already has the coax attached, and seals to the roof with a two-piece brass (or brass & stainless steel) machines assembly. The antenna of your choice then threads onto that base. The coax can be fished down using a fish tape or antenna whip if you don't feel like dropping the headliner, if you're feeling lucky and the stars are aligned, etc.
As for a diplexer, here's a decent example:
http://www.gigaparts.com/store.php?action=profile&sku=ZCM-CF-360A&gclid=COLd3bH66rECFQP0nAodPi8AjQ
The one line (that goes up to 30 MHz, labelled "HF") goes to the CB antenna; the second line (that goes to 470 MHz, labelled "6M-70cm) goes to the VHF antenna; and the port without a coax on it gets a jumper that goes to your CB.
On some wideband ham rigs that have separate HF and VHF/UHF connectors, it would actually be wired the "other way around", and the "empty port" would end up going to either a really wide band antenna (impractical), or through *another* diplexer at the end of a longish feedline, where the signal would get split out into HF and VHF/UHF antennas on either a vehicle or a base tower.
Note that this solution, with the diplexer and a typical NMO-style VHF whip from eekBay, is still gonna set you back $100 or so, plus shipping. OTOH, the mere presence of some printed schlock on the packaging of a CB whip, no matter the construction, is no more likely to defy the laws of physics and magically allow the 162.xxx energy from a NOAA weather transmitter to pass to your CB just because someone in marketing thought it should. Even a "full size" quarter wave CB antenna of about 108" is still about 6 quarter waves at the frequency of the weather transmission, but just having the extra "capture area" of the larger antenna, sans any matching network to shorten it physically, may allow the brute force of the high powered transmitter to sneak enough into your CB.
If I really, *really* had to make sure I knew about weather activity (and I often do), I'd have a separate radio that I use only for receive, hooked straight to a VHF-only antenna, separate feedline, etc. After 30 years in a place frequently ravaged by volcanic eruptions and tsunamis, I had the good sense (?!?) to move to the relative heart of Tornado Alley. At least in the past, I could see when the local volcanoes were erupting and had a couple of hours to make plans. Now I count on my $30 Midland weather alert radio to wake me when there's a tornado heading my way, or my aging Motherola mobile in the vehicle.
You'll have to come up with some kinda matrix of cost vs. convenience vs. reliability that works best for you. But you can't cheat physics.
73,
Handlebar