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When looking at an antenna system you need to consider at least two things, coax loss and your antenna gain. At UHF coax loss can be rather high for the typical type most people tend to use. It's a trade off between cost and cable loss. Less cable loss the bigger and more extensive the coax will be. I see many going for LMR-400. The loss at 450 MHz, GMRS is 462 MHz to 468 MHz approximately so we're close enough for this example, is 2.7 db per 100 feet. So if you have a 30 to 40 foot high tower or mast on the house you could easily use 75 feet of cable from the antenna to the radio. That works out to 2.03 db of loss so only 63 percent of your transmit power makes it to the antenna! What you would like to do is pick an antenna that has enough gain to make up, so to speak, for the cable losses at a minimum. A quick note here on gain, or loss, of every 3 db represents an increase by a factor of two, or a loss by 1/2. So a gain, or loss, of 6 db would be an increase by a factor 4, or a loss by a factor of 1/4. Now we have some things to look at very carefully with antennas. You will see antenna gains shown as some gain followed by "dbi" or "dbd". If it isn't shown or mentioned it's most likely in "dbi". The two gain spec's are NOT the same. The gain spec'd as "dbi" is the gain above a theoretical and impossible to build isotropic antenna. The gain spec'd as "dbd" is the gain above a dipole, really amounts to a 1/4 wave antenna on a ground plane. Think a cheap 1/4 wave magnet mount. The gain in "dbd" for a dipole is 0 while using "dbi" it's 2.15. Remember this is exactly the same antenna! Manufactures like to use the "dbi" spec because it inflates the gain by a couple of db. If you're not paying attention a cheap antenna rated in "dbi" may appear to be as good as a more expensive one rated in "dbd". Dishonest, no, but you need to be educated about what the spec's mean to make a good purchasing decision. So for example you might see a 1/4 wave antenna spec'd as 2.1 dbi. Hummm... Now getting back to the issue with cable loss you need a real gain of at least 2 dbd just to break even due to coax losses in the above example. Ideally you would like a lot more. Of course the antenna will be larger, longer, and more expensive. As the gain increases, it's usually at a spec'd center frequency, as you depart from that ideal point the gain tends to drop off. You want one designed and tuned close to center of the band of frequencies you want to operate on. In you case around 467 MHz to 468 MHz which are the repeater input frequencies for GMRS. I'm sure some members here have good recommendations. Also search past posts on the forums here for info.

968's advice is valid but the higher amperage supply I recommended will be less stressed and not prone to overheating and stressing its components. I run a 30 amp supply on my radios which pull 13 A at transmit.

Sufficient for what? If you are connecting to a local repeater across flat terrain you can probably get by with your current cabling. But, if your current cable is long, or of poor quality and your signal needs will be borderline, you should upgrade the cable. Connectors are harder, since most radios will have the same UHF connector as your CB. Personally, I’d try it with what’s in place, with a new antenna of course. But, do check the SWR first just to be sure you are safe.